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[openttd/fttd.git] / src / town_cmd.cpp

/* $Id$ */

/*
 * This file is part of OpenTTD.
 * OpenTTD is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, version 2.
 * OpenTTD is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
 * See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with OpenTTD. If not, see <http://www.gnu.org/licenses/>.
 */

/** @file town_cmd.cpp Handling of town tiles. */

#include "stdafx.h"

#include <bitset>

#include "road_internal.h" /* Cleaning up road bits */
#include "road_cmd.h"
#include "landscape.h"
#include "viewport_func.h"
#include "cmd_helper.h"
#include "command_func.h"
#include "industry.h"
#include "station_base.h"
#include "company_base.h"
#include "news_func.h"
#include "error.h"
#include "object.h"
#include "genworld.h"
#include "newgrf_debug.h"
#include "newgrf_house.h"
#include "newgrf_text.h"
#include "autoslope.h"
#include "map/zoneheight.h"
#include "map/road.h"
#include "map/tunnelbridge.h"
#include "strings_func.h"
#include "window_func.h"
#include "string.h"
#include "newgrf_cargo.h"
#include "cheat_type.h"
#include "animated_tile_func.h"
#include "date_func.h"
#include "subsidy_func.h"
#include "core/pool_func.hpp"
#include "town.h"
#include "townnamegen.h"
#include "townname_func.h"
#include "core/random_func.hpp"
#include "core/backup_type.hpp"
#include "depot_base.h"
#include "map/object.h"
#include "object_base.h"
#include "ai/ai.hpp"
#include "game/game.hpp"
#include "bridge.h"
#include "map/util.h"
#include "zoom_func.h"

#include "table/strings.h"
#include "table/town_land.h"

TownID _new_town_id;
uint32 _town_cargoes_accepted; ///< Bitmap of all cargoes accepted by houses.

/* Initialize the town-pool */
template<> Town::Pool Town::PoolItem::pool ("Town");
INSTANTIATE_POOL_METHODS(Town)

Town::~Town()
{
        free(this->name);
        free(this->text);

        if (CleaningPool()) return;

        /* Delete town authority window
         * and remove from list of sorted towns */
        DeleteWindowById(WC_TOWN_VIEW, this->index);

        /* Delete from town set */
        this->remove_from_tileset();

        /* Check no industry is related to us. */
        const Industry *i;
        FOR_ALL_INDUSTRIES(i) assert(i->town != this);

        /* ... and no object is related to us. */
        const Object *o;
        FOR_ALL_OBJECTS(o) assert(o->town != this);

        /* Check no tile is related to us. */
        for (TileIndex tile = 0; tile < MapSize(); ++tile) {
                if (IsHouseTile(tile)) {
                        assert(GetTownIndex(tile) != this->index);
                } else {
                        switch (GetTileType(tile)) {
                                case TT_MISC:
                                        if (IsTunnelTile(tile)) {
                                                assert(!IsTileOwner(tile, OWNER_TOWN) || ClosestTownFromTile(tile) != this);
                                                break;
                                        }
                                        if (!IsLevelCrossingTile(tile)) break;
                                        /* fall through */
                                case TT_ROAD:
                                        assert(!HasTownOwnedRoad(tile) || GetTownIndex(tile) != this->index);
                                        break;

                                default:
                                        break;
                        }
                }
        }

        /* Clear the persistent storage list. */
        this->psa_list.clear();

        DeleteSubsidyWith(ST_TOWN, this->index);
        DeleteNewGRFInspectWindow(GSF_FAKE_TOWNS, this->index);
        CargoPacket::InvalidateAllFrom(ST_TOWN, this->index);
        MarkWholeScreenDirty();
}


/**
 * Invalidating of the "nearest town cache" has to be done
 * after removing item from the pool.
 * @param index index of deleted item
 */
void Town::PostDestructor(size_t index)
{
        InvalidateWindowData(WC_TOWN_DIRECTORY, 0, 0);
        InvalidateWindowData(WC_SELECT_TOWN, 0);
        UpdateNearestTownForRoadTiles(false);

        /* Give objects a new home! */
        Object *o;
        FOR_ALL_OBJECTS(o) {
                if (o->town == NULL) o->town = CalcClosestTownFromTile(o->location.tile);
        }
}

/**
 * Return a random valid town.
 * @return random town, NULL if there are no towns
 */
/* static */ Town *Town::GetRandom()
{
        if (Town::GetNumItems() == 0) return NULL;
        int num = RandomRange((uint16)Town::GetNumItems());
        size_t index = MAX_UVALUE(size_t);

        while (num >= 0) {
                num--;
                index++;

                /* Make sure we have a valid town */
                while (!Town::IsValidID(index)) {
                        index++;
                        assert(index < Town::GetPoolSize());
                }
        }

        return Town::Get(index);
}

/**
 * Get the cost for removing this house
 * @return the cost (inflation corrected etc)
 */
Money HouseSpec::GetRemovalCost() const
{
        return (_price[PR_CLEAR_HOUSE] * this->removal_cost) >> 8;
}

static bool BuildTownHouse(Town *t, TileIndex tile);
static Town *CreateRandomTown(uint attempts, uint32 townnameparts, TownSize size, bool city, TownLayout layout);

static void TownDrawHouseLift(const TileInfo *ti)
{
        AddChildSpriteScreen (ti->vd, SPR_LIFT, PAL_NONE, 14, 60 - GetLiftPosition(ti->tile));
}

typedef void TownDrawTileProc(const TileInfo *ti);
static TownDrawTileProc * const _town_draw_tile_procs[1] = {
        TownDrawHouseLift
};

/**
 * Return a random direction
 *
 * @return a random direction
 */
static inline DiagDirection RandomDiagDir()
{
        return (DiagDirection)(3 & Random());
}

/**
 * House Tile drawing handler.
 * Part of the tile loop process
 * @param ti TileInfo of the tile to draw
 */
static void DrawTile_Town(TileInfo *ti)
{
        HouseID house_id = GetHouseType(ti->tile);

        if (house_id >= NEW_HOUSE_OFFSET) {
                /* Houses don't necessarily need new graphics. If they don't have a
                 * spritegroup associated with them, then the sprite for the substitute
                 * house id is drawn instead. */
                if (HouseSpec::Get(house_id)->grf_prop.spritegroup[0] != NULL) {
                        DrawNewHouseTile(ti, house_id);
                        return;
                } else {
                        house_id = HouseSpec::Get(house_id)->grf_prop.subst_id;
                }
        }

        /* Retrieve pointer to the draw town tile struct */
        const DrawBuildingsTileStruct *dcts = town_draw_tile_data[house_id][TileHash2Bit(ti->x, ti->y)][GetHouseBuildingStage(ti->tile)];

        if (ti->tileh != SLOPE_FLAT) DrawFoundation(ti, FOUNDATION_LEVELED);

        DrawGroundSprite (ti, dcts->ground.sprite, dcts->ground.pal);

        /* If houses are invisible, do not draw the upper part */
        if (IsInvisibilitySet(TO_HOUSES)) return;

        /* Add a house on top of the ground? */
        SpriteID image = dcts->building.sprite;
        if (image != 0) {
                AddSortableSpriteToDraw (ti->vd, image, dcts->building.pal,
                        ti->x + dcts->subtile_x,
                        ti->y + dcts->subtile_y,
                        dcts->width,
                        dcts->height,
                        dcts->dz,
                        ti->z,
                        IsTransparencySet(TO_HOUSES)
                );

                if (IsTransparencySet(TO_HOUSES)) return;
        }

        {
                int proc = dcts->draw_proc - 1;

                if (proc >= 0) _town_draw_tile_procs[proc](ti);
        }
}

static void DrawOldHouseTileInGUI (BlitArea *dpi, int x, int y,
        HouseID house_id, bool ground)
{
        /* Retrieve pointer to the draw town tile struct */
        const DrawBuildingsTileStruct *dcts = town_draw_tile_data[house_id][0][TOWN_HOUSE_COMPLETED];
        if (ground) {
                /* Draw the ground sprite */
                DrawSprite (dpi, dcts->ground.sprite, dcts->ground.pal, x, y);
        } else {
                /* Add a house on top of the ground? */
                if (dcts->building.sprite != 0) {
                        DrawSprite (dpi, dcts->building.sprite, dcts->building.pal,
                                        x + ScaleGUITrad (2 * (dcts->subtile_y - dcts->subtile_x)),
                                        y + ScaleGUITrad (dcts->subtile_x + dcts->subtile_y));
                }
                /* Draw the lift */
                if (dcts->draw_proc == 1) DrawSprite (dpi, SPR_LIFT, PAL_NONE, x - 18, y + 7);
        }
}

/**
 * Draw image of a house. Image will be centered between the \c left and the \c right and verticaly aligned to the \c bottom.
 *
 * @param house_id house type
 * @param dpi area to draw on
 * @param left left bound of the drawing area
 * @param top top bound of the drawing area
 * @param right right bound of the drawing area
 * @param bottom bottom bound of the drawing area
 */
void DrawHouseImage (HouseID house_id, BlitArea *dpi,
        int left, int top, int right, int bottom)
{
        BlitArea tmp_dpi;
        if (!InitBlitArea (dpi, &tmp_dpi, left, top, right - left + 1, bottom - top + 1)) return;

        const HouseSpec *hs = HouseSpec::Get(house_id);

        /* sprites are relative to the topmost pixel of the ground tile */
        uint x = (right - left + 1) / 2 - ScaleGUITrad (1);
        uint y = bottom - top + 1 - ScaleGUITrad (TILE_PIXELS - 1);
        uint half_tile_offset = ScaleGUITrad (TILE_PIXELS / 2);
        if (hs->building_flags & TILE_SIZE_1x2) x -= half_tile_offset;
        if (hs->building_flags & TILE_SIZE_2x1) x += half_tile_offset;
        if (hs->building_flags & BUILDING_HAS_2_TILES) y -= half_tile_offset;
        if (hs->building_flags & BUILDING_HAS_4_TILES) y -= half_tile_offset;

        bool new_house = false;
        if (house_id >= NEW_HOUSE_OFFSET) {
                /* Houses don't necessarily need new graphics. If they don't
                 * have a spritegroup associated with them, then the sprite
                 * for the substitute house id is drawn instead. */
                if (hs->grf_prop.spritegroup[0] != NULL) {
                        new_house = true;
                } else {
                        house_id = hs->grf_prop.subst_id;
                }
        }

        uint num_row = (hs->building_flags & BUILDING_2_TILES_X) ? 2 : 1;
        uint num_col = (hs->building_flags & BUILDING_2_TILES_Y) ? 2 : 1;

        Point pt[4];
        uint n = 0;
        for (uint row = 0; row < num_row; row++) {
                for (uint col = 0; col < num_col; col++) {
                        Point offset = RemapCoords (row * TILE_SIZE, col * TILE_SIZE, 0); // offset for current tile
                        pt[n].x = x + UnScaleByZoom (offset.x, ZOOM_LVL_GUI);
                        pt[n].y = y + UnScaleByZoom (offset.y, ZOOM_LVL_GUI);
                        n++;
                }
        }

        for (bool ground = true; ; ground = !ground) {
                for (uint i = 0; i < n; i++) {
                        HouseID hid = house_id + i;
                        if (new_house) {
                                DrawNewHouseTileInGUI (&tmp_dpi, pt[i].x, pt[i].y, hid, ground);
                        } else {
                                DrawOldHouseTileInGUI (&tmp_dpi, pt[i].x, pt[i].y, hid, ground);
                        }
                }
                if (!ground) break;
        }
}

static int GetSlopePixelZ_Town(TileIndex tile, uint x, uint y)
{
        return GetTileMaxPixelZ(tile);
}

/** Tile callback routine */
static Foundation GetFoundation_Town(TileIndex tile, Slope tileh)
{
        HouseID hid = GetHouseType(tile);

        /* For NewGRF house tiles we might not be drawing a foundation. We need to
         * account for this, as other structures should
         * draw the wall of the foundation in this case.
         */
        if (hid >= NEW_HOUSE_OFFSET) {
                const HouseSpec *hs = HouseSpec::Get(hid);
                if (hs->grf_prop.spritegroup[0] != NULL && HasBit(hs->callback_mask, CBM_HOUSE_DRAW_FOUNDATIONS)) {
                        uint32 callback_res = GetHouseCallback(CBID_HOUSE_DRAW_FOUNDATIONS, 0, 0, hid, Town::GetByTile(tile), tile);
                        if (callback_res != CALLBACK_FAILED && !ConvertBooleanCallback(hs->grf_prop.grffile, CBID_HOUSE_DRAW_FOUNDATIONS, callback_res)) return FOUNDATION_NONE;
                }
        }
        return FlatteningFoundation(tileh);
}

/**
 * Animate a tile for a town
 * Only certain houses can be animated
 * The newhouses animation supersedes regular ones
 * @param tile TileIndex of the house to animate
 */
static void AnimateTile_Town(TileIndex tile)
{
        if (GetHouseType(tile) >= NEW_HOUSE_OFFSET) {
                AnimateNewHouseTile(tile);
                return;
        }

        if (_tick_counter & 3) return;

        /* If the house is not one with a lift anymore, then stop this animating.
         * Not exactly sure when this happens, but probably when a house changes.
         * Before this was just a return...so it'd leak animated tiles..
         * That bug seems to have been here since day 1?? */
        if (!(HouseSpec::Get(GetHouseType(tile))->building_flags & BUILDING_IS_ANIMATED)) {
                DeleteAnimatedTile(tile);
                return;
        }

        if (!LiftHasDestination(tile)) {
                uint i;

                /* Building has 6 floors, number 0 .. 6, where 1 is illegal.
                 * This is due to the fact that the first floor is, in the graphics,
                 *  the height of 2 'normal' floors.
                 * Furthermore, there are 6 lift positions from floor N (incl) to floor N + 1 (excl) */
                do {
                        i = RandomRange(7);
                } while (i == 1 || i * 6 == GetLiftPosition(tile));

                SetLiftDestination(tile, i);
        }

        int pos = GetLiftPosition(tile);
        int dest = GetLiftDestination(tile) * 6;
        pos += (pos < dest) ? 1 : -1;
        SetLiftPosition(tile, pos);

        if (pos == dest) {
                HaltLift(tile);
                DeleteAnimatedTile(tile);
        }

        MarkTileDirtyByTile(tile);
}

/**
 * Resize the sign(label) of the town after changes in
 * population (creation or growth or else)
 */
void Town::UpdateVirtCoord()
{
        Point pt = RemapCoords2(TileX(this->xy) * TILE_SIZE, TileY(this->xy) * TILE_SIZE);
        SetDParam(0, this->index);
        SetDParam(1, this->cache.population);
        this->cache.sign.UpdatePosition(pt.x, pt.y - 24 * ZOOM_LVL_BASE,
                _settings_client.gui.population_in_label ? STR_VIEWPORT_TOWN_POP : STR_VIEWPORT_TOWN,
                STR_VIEWPORT_TOWN);

        SetWindowDirty(WC_TOWN_VIEW, this->index);
}

/** Update the virtual coords needed to draw the town sign for all towns. */
void UpdateAllTownVirtCoords()
{
        Town *t;

        FOR_ALL_TOWNS(t) {
                t->UpdateVirtCoord();
        }
}

/**
 * Change the towns population
 * @param t Town which population has changed
 * @param mod population change (can be positive or negative)
 */
static void ChangePopulation(Town *t, int mod)
{
        t->cache.population += mod;
        InvalidateWindowData(WC_TOWN_VIEW, t->index); // Cargo requirements may appear/vanish for small populations
        t->UpdateVirtCoord();

        InvalidateWindowData(WC_TOWN_DIRECTORY, 0, 1);
}

/**
 * Determines the world population
 * Basically, count population of all towns, one by one
 * @return uint32 the calculated population of the world
 */
uint32 GetWorldPopulation()
{
        uint32 pop = 0;
        const Town *t;

        FOR_ALL_TOWNS(t) pop += t->cache.population;
        return pop;
}

/**
 * Helper function for house completion stages progression
 * @param tile TileIndex of the house (or parts of it) to "grow"
 */
static void MakeSingleHouseBigger(TileIndex tile)
{
        assert(IsHouseTile(tile));

        /* progress in construction stages */
        IncHouseConstructionTick(tile);
        if (GetHouseConstructionTick(tile) != 0) return;

        AnimateNewHouseConstruction(tile);

        if (IsHouseCompleted(tile)) {
                /* Now that construction is complete, we can add the population of the
                 * building to the town. */
                ChangePopulation(Town::GetByTile(tile), HouseSpec::Get(GetHouseType(tile))->population);
                ResetHouseAge(tile);
        }
        MarkTileDirtyByTile(tile);
}

/**
 * Make the house advance in its construction stages until completion
 * @param tile TileIndex of house
 */
static void MakeTownHouseBigger(TileIndex tile)
{
        uint flags = HouseSpec::Get(GetHouseType(tile))->building_flags;
        if (flags & BUILDING_HAS_1_TILE)  MakeSingleHouseBigger(TILE_ADDXY(tile, 0, 0));
        if (flags & BUILDING_2_TILES_Y)   MakeSingleHouseBigger(TILE_ADDXY(tile, 0, 1));
        if (flags & BUILDING_2_TILES_X)   MakeSingleHouseBigger(TILE_ADDXY(tile, 1, 0));
        if (flags & BUILDING_HAS_4_TILES) MakeSingleHouseBigger(TILE_ADDXY(tile, 1, 1));
}

/**
 * Tile callback function.
 *
 * Periodic tic handler for houses and town
 * @param tile been asked to do its stuff
 */
static void TileLoop_Town(TileIndex tile)
{
        HouseID house_id = GetHouseType(tile);

        /* NewHouseTileLoop returns false if Callback 21 succeeded, i.e. the house
         * doesn't exist any more, so don't continue here. */
        if (house_id >= NEW_HOUSE_OFFSET && !NewHouseTileLoop(tile)) return;

        if (!IsHouseCompleted(tile)) {
                /* Construction is not completed. See if we can go further in construction*/
                MakeTownHouseBigger(tile);
                return;
        }

        const HouseSpec *hs = HouseSpec::Get(house_id);

        /* If the lift has a destination, it is already an animated tile. */
        if ((hs->building_flags & BUILDING_IS_ANIMATED) &&
                        house_id < NEW_HOUSE_OFFSET &&
                        !LiftHasDestination(tile) &&
                        Chance16(1, 2)) {
                AddAnimatedTile(tile);
        }

        Town *t = Town::GetByTile(tile);
        uint32 r = Random();

        StationFinder stations(TileArea(tile, 1, 1));

        if (HasBit(hs->callback_mask, CBM_HOUSE_PRODUCE_CARGO)) {
                for (uint i = 0; i < 256; i++) {
                        uint16 callback = GetHouseCallback(CBID_HOUSE_PRODUCE_CARGO, i, r, house_id, t, tile);

                        if (callback == CALLBACK_FAILED || callback == CALLBACK_HOUSEPRODCARGO_END) break;

                        CargoID cargo = GetCargoTranslation(GB(callback, 8, 7), hs->grf_prop.grffile);
                        if (cargo == CT_INVALID) continue;

                        uint amt = GB(callback, 0, 8);
                        if (amt == 0) continue;

                        uint moved = MoveGoodsToStation(cargo, amt, ST_TOWN, t->index, stations.GetStations());

                        const CargoSpec *cs = CargoSpec::Get(cargo);
                        t->supplied[cs->Index()].new_max += amt;
                        t->supplied[cs->Index()].new_act += moved;
                }
        } else {
                if (GB(r, 0, 8) < hs->population) {
                        uint amt = GB(r, 0, 8) / 8 + 1;

                        if (EconomyIsInRecession()) amt = (amt + 1) >> 1;
                        t->supplied[CT_PASSENGERS].new_max += amt;
                        t->supplied[CT_PASSENGERS].new_act += MoveGoodsToStation(CT_PASSENGERS, amt, ST_TOWN, t->index, stations.GetStations());
                }

                if (GB(r, 8, 8) < hs->mail_generation) {
                        uint amt = GB(r, 8, 8) / 8 + 1;

                        if (EconomyIsInRecession()) amt = (amt + 1) >> 1;
                        t->supplied[CT_MAIL].new_max += amt;
                        t->supplied[CT_MAIL].new_act += MoveGoodsToStation(CT_MAIL, amt, ST_TOWN, t->index, stations.GetStations());
                }
        }

        Backup<CompanyByte> cur_company(_current_company, OWNER_TOWN, FILE_LINE);

        if ((hs->building_flags & BUILDING_HAS_1_TILE) &&
                        HasBit(t->flags, TOWN_IS_GROWING) &&
                        CanDeleteHouse(tile) &&
                        GetHouseAge(tile) >= hs->minimum_life &&
                        --t->time_until_rebuild == 0) {
                t->time_until_rebuild = GB(r, 16, 8) + 192;

                ClearTownHouse(t, tile);

                /* Rebuild with another house? */
                if (GB(r, 24, 8) >= 12) BuildTownHouse(t, tile);
        }

        cur_company.Restore();
}

static CommandCost ClearTile_Town(TileIndex tile, DoCommandFlag flags)
{
        if (flags & DC_AUTO) return_cmd_error(STR_ERROR_BUILDING_MUST_BE_DEMOLISHED);
        if (!CanDeleteHouse(tile)) return CMD_ERROR;

        const HouseSpec *hs = HouseSpec::Get(GetHouseType(tile));

        CommandCost cost(EXPENSES_CONSTRUCTION);
        cost.AddCost(hs->GetRemovalCost());

        int rating = hs->remove_rating_decrease;
        Town *t = Town::GetByTile(tile);

        if (Company::IsValidID(_current_company)) {
                if (rating > t->ratings[_current_company] && !(flags & DC_NO_TEST_TOWN_RATING) && !_cheats.magic_bulldozer.value) {
                        SetDParam(0, t->index);
                        return_cmd_error(STR_ERROR_LOCAL_AUTHORITY_REFUSES_TO_ALLOW_THIS);
                }
        }

        ChangeTownRating(t, -rating, RATING_HOUSE_MINIMUM, flags);
        if (flags & DC_EXEC) {
                ClearTownHouse(t, tile);
        }

        return cost;
}

static void AddProducedCargo_Town(TileIndex tile, CargoArray &produced)
{
        HouseID house_id = GetHouseType(tile);
        const HouseSpec *hs = HouseSpec::Get(house_id);
        Town *t = Town::GetByTile(tile);

        if (HasBit(hs->callback_mask, CBM_HOUSE_PRODUCE_CARGO)) {
                for (uint i = 0; i < 256; i++) {
                        uint16 callback = GetHouseCallback(CBID_HOUSE_PRODUCE_CARGO, i, 0, house_id, t, tile);

                        if (callback == CALLBACK_FAILED || callback == CALLBACK_HOUSEPRODCARGO_END) break;

                        CargoID cargo = GetCargoTranslation(GB(callback, 8, 7), hs->grf_prop.grffile);

                        if (cargo == CT_INVALID) continue;
                        produced[cargo]++;
                }
        } else {
                if (hs->population > 0) {
                        produced[CT_PASSENGERS]++;
                }
                if (hs->mail_generation > 0) {
                        produced[CT_MAIL]++;
                }
        }
}

static inline void AddAcceptedCargoSetMask(CargoID cargo, uint amount, CargoArray &acceptance, uint32 *always_accepted)
{
        if (cargo == CT_INVALID || amount == 0) return;
        acceptance[cargo] += amount;
        SetBit(*always_accepted, cargo);
}

static void AddAcceptedCargo_Town(TileIndex tile, CargoArray &acceptance, uint32 *always_accepted)
{
        const HouseSpec *hs = HouseSpec::Get(GetHouseType(tile));
        CargoID accepts[3];

        /* Set the initial accepted cargo types */
        for (uint8 i = 0; i < lengthof(accepts); i++) {
                accepts[i] = hs->accepts_cargo[i];
        }

        /* Check for custom accepted cargo types */
        if (HasBit(hs->callback_mask, CBM_HOUSE_ACCEPT_CARGO)) {
                uint16 callback = GetHouseCallback(CBID_HOUSE_ACCEPT_CARGO, 0, 0, GetHouseType(tile), Town::GetByTile(tile), tile);
                if (callback != CALLBACK_FAILED) {
                        /* Replace accepted cargo types with translated values from callback */
                        accepts[0] = GetCargoTranslation(GB(callback,  0, 5), hs->grf_prop.grffile);
                        accepts[1] = GetCargoTranslation(GB(callback,  5, 5), hs->grf_prop.grffile);
                        accepts[2] = GetCargoTranslation(GB(callback, 10, 5), hs->grf_prop.grffile);
                }
        }

        /* Check for custom cargo acceptance */
        if (HasBit(hs->callback_mask, CBM_HOUSE_CARGO_ACCEPTANCE)) {
                uint16 callback = GetHouseCallback(CBID_HOUSE_CARGO_ACCEPTANCE, 0, 0, GetHouseType(tile), Town::GetByTile(tile), tile);
                if (callback != CALLBACK_FAILED) {
                        AddAcceptedCargoSetMask(accepts[0], GB(callback, 0, 4), acceptance, always_accepted);
                        AddAcceptedCargoSetMask(accepts[1], GB(callback, 4, 4), acceptance, always_accepted);
                        if (_settings_game.game_creation.landscape != LT_TEMPERATE && HasBit(callback, 12)) {
                                /* The 'S' bit indicates food instead of goods */
                                AddAcceptedCargoSetMask(CT_FOOD, GB(callback, 8, 4), acceptance, always_accepted);
                        } else {
                                AddAcceptedCargoSetMask(accepts[2], GB(callback, 8, 4), acceptance, always_accepted);
                        }
                        return;
                }
        }

        /* No custom acceptance, so fill in with the default values */
        for (uint8 i = 0; i < lengthof(accepts); i++) {
                AddAcceptedCargoSetMask(accepts[i], hs->cargo_acceptance[i], acceptance, always_accepted);
        }
}

static void GetTileDesc_Town(TileIndex tile, TileDesc *td)
{
        const HouseID house = GetHouseType(tile);
        const HouseSpec *hs = HouseSpec::Get(house);
        bool house_completed = IsHouseCompleted(tile);

        td->str = hs->building_name;

        uint16 callback_res = GetHouseCallback(CBID_HOUSE_CUSTOM_NAME, house_completed ? 1 : 0, 0, house, Town::GetByTile(tile), tile);
        if (callback_res != CALLBACK_FAILED && callback_res != 0x400) {
                if (callback_res > 0x400) {
                        ErrorUnknownCallbackResult(hs->grf_prop.grffile->grfid, CBID_HOUSE_CUSTOM_NAME, callback_res);
                } else {
                        StringID new_name = GetGRFStringID(hs->grf_prop.grffile->grfid, 0xD000 + callback_res);
                        if (new_name != STR_NULL && new_name != STR_UNDEFINED) {
                                td->str = new_name;
                        }
                }
        }

        if (!house_completed) {
                td->dparam = td->str;
                td->str = STR_LAI_TOWN_INDUSTRY_DESCRIPTION_UNDER_CONSTRUCTION;
        }

        if (hs->grf_prop.grffile != NULL) {
                const GRFConfig *gc = GetGRFConfig(hs->grf_prop.grffile->grfid);
                td->grf = gc->GetName();
        }

        td->owner[0] = OWNER_TOWN;
}

static void ChangeTileOwner_Town(TileIndex tile, Owner old_owner, Owner new_owner)
{
        /* not used */
}

/** Update the total cargo acceptance of the whole town.
 * @param t The town to update.
 */
void UpdateTownCargoTotal(Town *t)
{
        t->cargo_accepted_total = 0;

        const TileArea &area = t->cargo_accepted.GetArea();
        TILE_AREA_LOOP(tile, area) {
                if (TileX(tile) % AcceptanceMatrix::GRID == 0 && TileY(tile) % AcceptanceMatrix::GRID == 0) {
                        t->cargo_accepted_total |= t->cargo_accepted[tile];
                }
        }
}

/**
 * Update accepted town cargoes around a specific tile.
 * @param t The town to update.
 * @param start Update the values around this tile.
 * @param update_total Set to true if the total cargo acceptance should be updated.
 */
static void UpdateTownCargoes(Town *t, TileIndex start, bool update_total = true)
{
        CargoArray accepted, produced;
        uint32 dummy;

        /* Gather acceptance for all houses in an area around the start tile.
         * The area is composed of the square the tile is in, extended one square in all
         * directions as the coverage area of a single station is bigger than just one square. */
        TileArea area = AcceptanceMatrix::GetAreaForTile(start, 1);
        TILE_AREA_LOOP(tile, area) {
                if (!IsHouseTile(tile) || GetTownIndex(tile) != t->index) continue;

                AddAcceptedCargo_Town(tile, accepted, &dummy);
                AddProducedCargo_Town(tile, produced);
        }

        /* Create bitmap of produced and accepted cargoes. */
        uint32 acc = 0;
        for (uint cid = 0; cid < NUM_CARGO; cid++) {
                if (accepted[cid] >= 8) SetBit(acc, cid);
                if (produced[cid] > 0) SetBit(t->cargo_produced, cid);
        }
        t->cargo_accepted[start] = acc;

        if (update_total) UpdateTownCargoTotal(t);
}

/** Update cargo acceptance for the complete town.
 * @param t The town to update.
 */
void UpdateTownCargoes(Town *t)
{
        t->cargo_produced = 0;

        const TileArea &area = t->cargo_accepted.GetArea();
        if (area.tile == INVALID_TILE) return;

        /* Update acceptance for each grid square. */
        TILE_AREA_LOOP(tile, area) {
                if (TileX(tile) % AcceptanceMatrix::GRID == 0 && TileY(tile) % AcceptanceMatrix::GRID == 0) {
                        UpdateTownCargoes(t, tile, false);
                }
        }

        /* Update the total acceptance. */
        UpdateTownCargoTotal(t);
}

/** Updates the bitmap of all cargoes accepted by houses. */
void UpdateTownCargoBitmap()
{
        Town *town;
        _town_cargoes_accepted = 0;

        FOR_ALL_TOWNS(town) {
                _town_cargoes_accepted |= town->cargo_accepted_total;
        }
}

static bool GrowTown(Town *t);

void OnTick_Town()
{
        if (_game_mode == GM_EDITOR) return;

        Town *t;
        FOR_ALL_TOWNS(t) {
                /* Run town tick at regular intervals, but not all at once. */
                if ((_tick_counter + t->index) % TOWN_GROWTH_TICKS == 0
                                && HasBit(t->flags, TOWN_IS_GROWING)) {
                        if (t->grow_counter > 0) {
                                t->grow_counter--;
                        } else if (GrowTown(t)) {
                                t->grow_counter = t->growth_rate & (~TOWN_GROW_RATE_CUSTOM);
                        }
                }
        }
}

/**
 * Return the RoadBits of a tile
 *
 * @note There are many other functions doing things like that.
 * @note Needs to be checked for needlessness.
 * @param tile The tile we want to analyse
 * @return The roadbits of the given tile
 */
static RoadBits GetTownRoadBits(TileIndex tile)
{
        if (IsRoadDepotTile(tile) || IsStandardRoadStopTile(tile)) return ROAD_NONE;

        return GetAnyRoadBits(tile, ROADTYPE_ROAD, true);
}

/**
 * Check for parallel road inside a given distance.
 *   Assuming a road from (tile - TileOffsByDiagDir(dir)) to tile,
 *   is there a parallel road left or right of it within distance dist_multi?
 *
 * @param tile current tile
 * @param dir target direction
 * @param dist_multi distance multiplayer
 * @return true if there is a parallel road
 */
static bool IsNeighborRoadTile(TileIndex tile, const DiagDirection dir, uint dist_multi)
{
        if (!IsValidTile(tile)) return false;

        /* Lookup table for the used diff values */
        const TileIndexDiff tid_lt[3] = {
                TileOffsByDiagDir(ChangeDiagDir(dir, DIAGDIRDIFF_90RIGHT)),
                TileOffsByDiagDir(ChangeDiagDir(dir, DIAGDIRDIFF_90LEFT)),
                TileOffsByDiagDir(ReverseDiagDir(dir)),
        };

        dist_multi = (dist_multi + 1) * 4;
        for (uint pos = 4; pos < dist_multi; pos++) {
                /* Go (pos / 4) tiles to the left or the right */
                TileIndexDiff cur = tid_lt[(pos & 1) ? 0 : 1] * (pos / 4);

                /* Use the current tile as origin, or go one tile backwards */
                if (pos & 2) cur += tid_lt[2];

                /* Test for roadbit parallel to dir and facing towards the middle axis */
                if (IsValidTile(tile + cur) &&
                                GetTownRoadBits(TILE_ADD(tile, cur)) & DiagDirToRoadBits((pos & 2) ? dir : ReverseDiagDir(dir))) return true;
        }
        return false;
}

/**
 * Check if a Road is allowed on a given tile
 *
 * @param t The current town
 * @param tile The target tile
 * @param dir The direction in which we want to extend the town
 * @return true if it is allowed else false
 */
static bool IsRoadAllowedHere(Town *t, TileIndex tile, DiagDirection dir)
{
        if (DistanceFromEdge(tile) == 0) return false;

        /* Prevent towns from building roads under bridges along the bridge. Looks silly. */
        if (HasBridgeAbove(tile) && GetBridgeAxis(tile) == DiagDirToAxis(dir)) return false;

        /* Check if there already is a road at this point? */
        if (GetTownRoadBits(tile) == ROAD_NONE) {
                /* No, try if we are able to build a road piece there.
                 * If that fails clear the land, and if that fails exit.
                 * This is to make sure that we can build a road here later. */
                if (DoCommand(tile, ((dir == DIAGDIR_NW || dir == DIAGDIR_SE) ? ROAD_Y : ROAD_X), 0, DC_AUTO, CMD_BUILD_ROAD).Failed() &&
                                DoCommand(tile, 0, 0, DC_AUTO, CMD_LANDSCAPE_CLEAR).Failed()) {
                        return false;
                }
        }

        Slope cur_slope = _settings_game.construction.build_on_slopes ? GetFoundationSlope(tile) : GetTileSlope(tile);
        bool ret = !IsNeighborRoadTile(tile, dir, t->layout == TL_ORIGINAL ? 1 : 2);
        if (cur_slope == SLOPE_FLAT) return ret;

        Slope desired_slope = (dir == DIAGDIR_NW || dir == DIAGDIR_SE) ? SLOPE_NW : SLOPE_NE;
        if (desired_slope == cur_slope || ComplementSlope(desired_slope) == cur_slope) return ret;

        /* If the tile is not a slope in the right direction, then
         * maybe terraform some. */
        if (Chance16(1, 8)) {
                /* Note: Do not replace "^ SLOPE_ELEVATED" with ComplementSlope(). The slope might be steep. */
                bool terraform = !_generating_world && Chance16(1, 10) &&
                                DoCommand(tile, Chance16(1, 16) ? cur_slope : cur_slope ^ SLOPE_ELEVATED, 0,
                                        DC_EXEC | DC_AUTO | DC_NO_WATER, CMD_TERRAFORM_LAND).Succeeded();
                if (!terraform && Chance16(1, 3)) {
                        /* We can consider building on the slope, though. */
                        return ret;
                }
        }
        return false;
}

static bool TerraformTownTile(TileIndex tile, int edges, int dir)
{
        assert(tile < MapSize());

        CommandCost r = DoCommand(tile, edges, dir, DC_AUTO | DC_NO_WATER, CMD_TERRAFORM_LAND);
        if (r.Failed() || r.GetCost() >= (_price[PR_TERRAFORM] + 2) * 8) return false;
        DoCommand(tile, edges, dir, DC_AUTO | DC_NO_WATER | DC_EXEC, CMD_TERRAFORM_LAND);
        return true;
}

static void LevelTownLand(TileIndex tile)
{
        assert(tile < MapSize());

        /* Don't terraform if land is plain or if there's a house there. */
        if (IsHouseTile(tile)) return;
        Slope tileh = GetTileSlope(tile);
        if (tileh == SLOPE_FLAT) return;

        /* First try up, then down */
        if (!TerraformTownTile(tile, ~tileh & SLOPE_ELEVATED, 1)) {
                TerraformTownTile(tile, tileh & SLOPE_ELEVATED, 0);
        }
}

/**
 * Generate the RoadBits of a grid tile
 *
 * @param t current town
 * @param tile tile in reference to the town
 * @param dir The direction to which we are growing ATM
 * @return the RoadBit of the current tile regarding
 *  the selected town layout
 */
static RoadBits GetTownRoadGridElement(Town *t, TileIndex tile, DiagDirection dir)
{
        /* align the grid to the downtown */
        CoordDiff grid_pos = TileCoordDiff(t->xy, tile); // Vector from downtown to the tile
        RoadBits rcmd = ROAD_NONE;

        switch (t->layout) {
                default: NOT_REACHED();

                case TL_2X2_GRID:
                        if ((grid_pos.x % 3) == 0) rcmd |= ROAD_Y;
                        if ((grid_pos.y % 3) == 0) rcmd |= ROAD_X;
                        break;

                case TL_3X3_GRID:
                        if ((grid_pos.x % 4) == 0) rcmd |= ROAD_Y;
                        if ((grid_pos.y % 4) == 0) rcmd |= ROAD_X;
                        break;
        }

        /* Optimise only X-junctions */
        if (rcmd != ROAD_ALL) return rcmd;

        RoadBits rb_template;

        switch (GetTileSlope(tile)) {
                default:       rb_template = ROAD_ALL; break;
                case SLOPE_W:  rb_template = ROAD_NW | ROAD_SW; break;
                case SLOPE_SW: rb_template = ROAD_Y  | ROAD_SW; break;
                case SLOPE_S:  rb_template = ROAD_SW | ROAD_SE; break;
                case SLOPE_SE: rb_template = ROAD_X  | ROAD_SE; break;
                case SLOPE_E:  rb_template = ROAD_SE | ROAD_NE; break;
                case SLOPE_NE: rb_template = ROAD_Y  | ROAD_NE; break;
                case SLOPE_N:  rb_template = ROAD_NE | ROAD_NW; break;
                case SLOPE_NW: rb_template = ROAD_X  | ROAD_NW; break;
                case SLOPE_STEEP_W:
                case SLOPE_STEEP_S:
                case SLOPE_STEEP_E:
                case SLOPE_STEEP_N:
                        rb_template = ROAD_NONE;
                        break;
        }

        /* Stop if the template is compatible to the growth dir */
        if (DiagDirToRoadBits(ReverseDiagDir(dir)) & rb_template) return rb_template;
        /* If not generate a straight road in the direction of the growth */
        return DiagDirToRoadBits(dir) | DiagDirToRoadBits(ReverseDiagDir(dir));
}

/**
 * Grows the town with an extra house.
 *  Check if there are enough neighbor house tiles
 *  next to the current tile. If there are enough
 *  add another house.
 *
 * @param t The current town
 * @param tile The target tile for the extra house
 * @return true if an extra house has been added
 */
static bool GrowTownWithExtraHouse(Town *t, TileIndex tile)
{
        /* We can't look further than that. */
        if (DistanceFromEdge(tile) == 0) return false;

        uint counter = 0; // counts the house neighbor tiles

        /* Check the tiles E,N,W and S of the current tile for houses */
        for (DiagDirection dir = DIAGDIR_BEGIN; dir < DIAGDIR_END; dir++) {
                /* Count both void and house tiles for checking whether there
                 * are enough houses in the area. This to make it likely that
                 * houses get build up to the edge of the map. */
                TileIndex tt = TileAddByDiagDir(tile, dir);
                if (IsHouseTile(tt) || IsVoidTile(tt)) {
                        counter++;
                }

                /* If there are enough neighbors stop here */
                if (counter >= 3) {
                        return BuildTownHouse (t, tile);
                }
        }
        return false;
}

/**
 * Grows the town with a bridge.
 *  At first we check if a bridge is reasonable.
 *  If so we check if we are able to build it.
 *
 * @param t The current town
 * @param tile The current tile
 * @param bridge_dir The valid direction in which to grow a bridge
 * @return true if a bridge has been build else false
 */
static bool GrowTownWithBridge(const Town *t, const TileIndex tile, const DiagDirection bridge_dir)
{
        assert(bridge_dir < DIAGDIR_END);

        const Slope slope = GetTileSlope(tile);

        /* Assure that the bridge is connectable to the start side */
        if (!(GetTownRoadBits(TileAddByDiagDir(tile, ReverseDiagDir(bridge_dir))) & DiagDirToRoadBits(bridge_dir))) return false;

        /* We are in the right direction */
        const int delta = TileOffsByDiagDir(bridge_dir);

        uint bridge_length = 0;               // This value stores the length of the possible bridge
        TileIndex bridge_tile = tile + delta; // Used to store the other waterside

        if (slope == SLOPE_FLAT) {
                /* Bridges starting on flat tiles are only allowed when crossing rivers. */
                while (IsValidTile(bridge_tile) && IsPlainWaterTile(bridge_tile) && !IsSea(bridge_tile)) {
                        /* Allow to cross rivers, not big lakes. */
                        if (bridge_length >= 3) return false;
                        bridge_length++;
                        bridge_tile += delta;
                };
        } else {
                /* Make sure the direction is compatible with the slope.
                 * Well we check if the slope has an up bit set in the
                 * reverse direction. */
                if (slope & InclinedSlope(bridge_dir)) return false;

                while (IsValidTile(bridge_tile) && IsPlainWaterTile(bridge_tile)) {
                        /* Max 10-tile long bridges */
                        if (bridge_length >= 10) return false;
                        bridge_length++;
                        bridge_tile += delta;
                };
        }

        /* no water tiles in between? */
        if (bridge_length == 0) return false;

        std::bitset <MAX_BRIDGES> tried;
        uint n = MAX_BRIDGES;
        byte bridge_type = RandomRange (n);

        for (;;) {
                /* Can we actually build the bridge? */
                if (DoCommand(tile, bridge_tile, bridge_type | ROADTYPES_ROAD << 8 | TRANSPORT_ROAD << 12 | t->index << 16, CommandFlagsToDCFlags(GetCommandFlags(CMD_BUILD_BRIDGE)), CMD_BUILD_BRIDGE).Succeeded()) {
                        DoCommand(tile, bridge_tile, bridge_type | ROADTYPES_ROAD << 8 | TRANSPORT_ROAD << 12 | t->index << 16, DC_EXEC | CommandFlagsToDCFlags(GetCommandFlags(CMD_BUILD_BRIDGE)), CMD_BUILD_BRIDGE);
                        return true;
                }

                /* Try a different bridge. */
                tried[bridge_type] = true;
                n--;
                assert (n + tried.count() == MAX_BRIDGES);
                if (n == 0) break;

                bridge_type = 0;
                uint i = RandomRange (n);
                while (tried[bridge_type] || (i-- > 0)) {
                        bridge_type++;
                        assert (bridge_type < MAX_BRIDGES);
                }
        }

        /* Quit if no bridge can be built. */
        return false;
}

/**
 * Grows the town with either a bridge or a road piece.
 *
 * @param t The current town
 * @param tile The current tile
 * @param target_dir The target road dir
 * @param rcmd The RoadBits we want to build on the tile
 * @return true if the RoadBits have been added else false
 */
static bool GrowTownWithRoad(const Town *t, TileIndex tile, DiagDirection target_dir, RoadBits rcmd)
{
        /* Make the roads look nicer */
        rcmd = CleanUpRoadBits(tile, rcmd);
        if (rcmd == ROAD_NONE) return false;

        /* Only use the target direction for bridges to ensure they're connected.
         * The target_dir is as computed previously according to town layout, so
         * it will match it perfectly. */
        return GrowTownWithBridge (t, tile, target_dir)
                || DoCommand (tile, rcmd, t->index, DC_EXEC | DC_AUTO | DC_NO_WATER, CMD_BUILD_ROAD).Succeeded();
}

/**
 * Grows the given town at a tile where there are no roads.
 * @param t The current town
 * @param tile The current tile
 * @param target_dir The target road dir
 * @return Whether a road was built
 */
static bool GrowTown_NewRoad (Town *t, TileIndex tile, DiagDirection target_dir)
{
        if (!_settings_game.economy.allow_town_roads && !_generating_world) return false;
        if (!_settings_game.economy.allow_town_level_crossings && IsRailwayTile(tile)) return false;

        /* Remove hills etc */
        if (!_settings_game.construction.build_on_slopes || Chance16(1, 6)) LevelTownLand(tile);

        RoadBits rcmd = ROAD_NONE;  // RoadBits for the road construction command

        /* Is a road allowed here? */
        switch (t->layout) {
                default: NOT_REACHED();

                case TL_3X3_GRID:
                case TL_2X2_GRID:
                        rcmd = GetTownRoadGridElement (t, tile, target_dir);
                        if (rcmd == ROAD_NONE) return false;
                        break;

                case TL_BETTER_ROADS:
                case TL_ORIGINAL:
                        if (!IsRoadAllowedHere (t, tile, target_dir)) return false;

                        DiagDirection source_dir = ReverseDiagDir(target_dir);

                        if (Chance16(1, 6)) {
                                /* Randomize a new target dir */
                                target_dir = ChangeDiagDir (target_dir, Chance16(1, 2) ? DIAGDIRDIFF_90RIGHT : DIAGDIRDIFF_90LEFT);
                        }

                        if (!IsRoadAllowedHere (t, TileAddByDiagDir(tile, target_dir), target_dir)) {
                                /* A road is not allowed to continue the randomized road,
                                 *  return if the road we're trying to build is curved. */
                                if (target_dir != ReverseDiagDir(source_dir)) return false;

                                /* Return if neither side of the new road is a house */
                                if (!IsHouseTile(TileAddByDiagDir(tile, ChangeDiagDir(target_dir, DIAGDIRDIFF_90RIGHT))) &&
                                                !IsHouseTile(TileAddByDiagDir(tile, ChangeDiagDir(target_dir, DIAGDIRDIFF_90LEFT)))) {
                                        return false;
                                }

                                /* That means that the road is only allowed if there is a house
                                 *  at any side of the new road. */
                        }

                        rcmd = DiagDirToRoadBits(target_dir) | DiagDirToRoadBits(source_dir);
                        break;
        }

        /* Return if a water tile */
        if (HasTileWaterGround(tile)) return false;

        return GrowTownWithRoad (t, tile, target_dir, rcmd);
}

/**
 * Grows the given town at a tile where there is an unconnected road.
 * @param t The current town
 * @param tile The current tile
 * @param target_dir The target road dir
 * @param cur_rb The current tile RoadBits
 * @return Whether a road piece was built
 */
static bool GrowTown_UnconnectedRoad (Town *t, TileIndex tile, DiagDirection target_dir, RoadBits cur_rb)
{
        /* Continue building on a partial road.
         * Should be always OK, so we only generate
         * the fitting RoadBits */

        if (!_settings_game.economy.allow_town_roads && !_generating_world) return false;

        RoadBits rcmd = ROAD_NONE;  // RoadBits for the road construction command

        switch (t->layout) {
                default: NOT_REACHED();

                case TL_3X3_GRID:
                case TL_2X2_GRID:
                        rcmd = GetTownRoadGridElement (t, tile, target_dir);
                        break;

                case TL_BETTER_ROADS:
                case TL_ORIGINAL:
                        rcmd = DiagDirToRoadBits(ReverseDiagDir(target_dir));
                        break;
        }

        return GrowTownWithRoad (t, tile, target_dir, rcmd);
}

/* Describe the possible results of GrowTown_ConnectedRoad. */
enum TownGrowthResult {
        GROWTH_CONTINUE, ///< continue searching
        GROWTH_FAILURE,  ///< growth failed, stop searching
        GROWTH_SUCCESS,  ///< growth succeeded, stop searching
};

/**
 * Grows the given town at a tile where there is a connected road.
 * @param t The current town
 * @param tile The current tile
 * @param target_dir The target road dir
 * @param cur_rb The current tile RoadBits
 * @return The result of the growth attempt
 */
static TownGrowthResult GrowTown_ConnectedRoad (Town *t, TileIndex tile, DiagDirection target_dir, RoadBits cur_rb)
{
        /* Possibly extend the road in a direction.
         * Randomize a direction and if it has a road, bail out. */
        target_dir = RandomDiagDir();
        if (cur_rb & DiagDirToRoadBits(target_dir)) return GROWTH_CONTINUE;

        /* This is the tile we will reach if we extend to this direction. */
        TileIndex house_tile = TileAddByDiagDir(tile, target_dir); // position of a possible house

        /* Don't walk into water. */
        if (HasTileWaterGround(house_tile)) return GROWTH_CONTINUE;

        if (!IsValidTile(house_tile)) return GROWTH_CONTINUE;

        bool allow_house = true; // Value which decides if we want to construct a house
        RoadBits rcmd = ROAD_NONE;  // RoadBits for the road construction command
        bool house_built = false;   // Whether a house has been built

        if (_settings_game.economy.allow_town_roads || _generating_world) {
                switch (t->layout) {
                        default: NOT_REACHED();

                        case TL_3X3_GRID: // Use 2x2 grid afterwards!
                                house_built = GrowTownWithExtraHouse (t, TileAddByDiagDir(house_tile, target_dir));
                                /* fall through */
                        case TL_2X2_GRID:
                                rcmd = GetTownRoadGridElement (t, house_tile, target_dir);
                                allow_house = (rcmd == ROAD_NONE);
                                break;

                        case TL_BETTER_ROADS: // Use original afterwards!
                                house_built = GrowTownWithExtraHouse (t, TileAddByDiagDir(house_tile, target_dir));
                                /* fall through */
                        case TL_ORIGINAL:
                                /* Allow a house at the edge. 60% chance or
                                 * always ok if no road allowed. */
                                rcmd = DiagDirToRoadBits(target_dir);
                                allow_house = (!IsRoadAllowedHere (t, house_tile, target_dir) || Chance16(6, 10));
                                break;
                }
        }

        if (allow_house) {
                /* Build a house, but not if there already is a house there. */
                if (!IsHouseTile(house_tile)) {
                        /* Level the land if possible */
                        if (Chance16(1, 6)) LevelTownLand(house_tile);

                        /* And build a house.
                         * Set result to -1 if we managed to build it. */
                        if (BuildTownHouse (t, house_tile)) house_built = true;
                }
                return house_built ? GROWTH_SUCCESS : GROWTH_CONTINUE;
        }

        return GrowTownWithRoad (t, tile, target_dir, rcmd) ? GROWTH_SUCCESS : GROWTH_FAILURE;
}

/**
 * Simple heuristic to check if a tile may be usable for town growth.
 * @param tile The tile to check.
 * @return Whether the tile is usable.
 */
static bool GrowTownTileUsable (TileIndex tile)
{
        assert (tile < MapSize());

        switch (GetTileType (tile)) {
                case TT_GROUND:
                        return !IsTileSubtype (tile, TT_GROUND_VOID);

                case TT_WATER:
                        return IsCoast (tile);

                case TT_RAILWAY:
                case TT_ROAD:
                        return true;

                case TT_MISC:
                        switch (GetTileSubtype(tile)) {
                                case TT_MISC_CROSSING: return true;
                                case TT_MISC_TUNNEL:   return GetTunnelTransportType(tile) == TRANSPORT_ROAD;
                                default: return false;
                        }
                        break;

                case TT_STATION:
                        return IsDriveThroughStopTile (tile);


                default: return false;
        }
}

/**
 * Returns "growth" if a house was built, or no if the build failed.
 * @param t town to inquiry
 * @param tile to inquiry
 * @return whether expansion was possible
 */
static bool GrowTownFromTile (Town *t, TileIndex tile)
{
        DiagDirection target_dir = DIAGDIR_END; // The direction in which we want to extend the town

        assert(tile < MapSize());

        /* Number of times to search.
         * Better roads, 2X2 and 3X3 grid grow quite fast so we give
         * them a little handicap. */
        uint iterations;
        switch (t->layout) {
                case TL_BETTER_ROADS:
                        iterations = 10 + t->cache.num_houses * 2 / 9;
                        break;

                case TL_3X3_GRID:
                case TL_2X2_GRID:
                        iterations = 10 + t->cache.num_houses * 1 / 9;
                        break;

                default:
                        iterations = 10 + t->cache.num_houses * 4 / 9;
                        break;
        }

        while (iterations-- > 0) {
                RoadBits cur_rb = GetTownRoadBits(tile); // The RoadBits of the current tile

                /* Try to grow the town from this point */
                assert(tile < MapSize());
                assert((cur_rb == ROAD_NONE) || !HasTileWaterGround(tile));

                if (cur_rb == ROAD_NONE) {
                        assert (IsValidDiagDirection(target_dir));
                        return GrowTown_NewRoad (t, tile, target_dir);

                } else if (target_dir != DIAGDIR_END && !(cur_rb & DiagDirToRoadBits(ReverseDiagDir(target_dir)))) {
                        return GrowTown_UnconnectedRoad (t, tile, target_dir, cur_rb);

                } else if (!IsRoadBridgeTile(tile) && !IsTunnelTile(tile)) {
                        switch (GrowTown_ConnectedRoad (t, tile, target_dir, cur_rb)) {
                                case GROWTH_CONTINUE: break;
                                case GROWTH_FAILURE:  return false;
                                case GROWTH_SUCCESS:  return true;
                        }
                }

                if (IsTunnelTile(tile)) {
                        /* Reached a tunnel. Continue at the other end if this
                         * is not the first tile, or half of the times if it is. */
                        assert (maptile_is_road_tunnel(tile));

                        if (target_dir == DIAGDIR_END) {
                                if (Chance16(1, 2)) tile = GetOtherTunnelEnd (tile);
                                target_dir = ReverseDiagDir (GetTunnelBridgeDirection(tile));
                        } else {
                                if (GetTunnelBridgeDirection(tile) != target_dir) return false;
                                tile = GetOtherTunnelEnd (tile);
                        }

                        tile = TileAddByDiagDir (tile, target_dir);
                        if ((IsRoadBridgeTile(tile) || IsTunnelTile(tile))
                                        && GetTunnelBridgeDirection(tile) == (ReverseDiagDir(target_dir))) {
                                return false;
                        }
                } else {
                        /* Exclude the source position from the bitmask
                         * and return if no more road blocks available */
                        if (target_dir != DIAGDIR_END) cur_rb &= ~DiagDirToRoadBits(ReverseDiagDir(target_dir));

                        /* Select a random bit from the blockmask, walk a step
                         * and continue the search from there. */
                        TileIndex target_tile;
                        for (;;) {
                                if (cur_rb == ROAD_NONE) return false;

                                RoadBits connect_rb;
                                do {
                                        target_dir = RandomDiagDir();
                                        connect_rb = DiagDirToRoadBits (target_dir);
                                } while (!(cur_rb & connect_rb));
                                cur_rb ^= connect_rb;

                                if (IsRoadBridgeTile(tile) && target_dir == GetTunnelBridgeDirection(tile)) {
                                        target_tile = GetOtherBridgeEnd (tile);
                                        break;
                                }

                                target_tile = TileAddByDiagDir (tile, target_dir);
                                if ((IsRoadBridgeTile (target_tile) || IsTunnelTile (target_tile))
                                                && GetTunnelBridgeDirection (target_tile) == (ReverseDiagDir (target_dir))) {
                                        continue;
                                }

                                if (_settings_game.economy.allow_town_roads || _generating_world) {
                                        if (GrowTownTileUsable (target_tile)) break;
                                } else {
                                        connect_rb = MirrorRoadBits (connect_rb);
                                        RoadBits target_rb = GetTownRoadBits (target_tile);
                                        if ((target_rb & connect_rb) != 0 && (target_rb != connect_rb)) break;
                                }
                        }
                        tile = target_tile;
                }

                if ((IsRoadTile(tile) || IsLevelCrossingTile(tile)) && HasTileRoadType(tile, ROADTYPE_ROAD)) {
                        /* Don't allow building over roads of other cities */
                        if (IsRoadOwner(tile, ROADTYPE_ROAD, OWNER_TOWN) && Town::GetByTile(tile) != t) {
                                return true;
                        } else if (IsRoadOwner(tile, ROADTYPE_ROAD, OWNER_NONE) && _game_mode == GM_EDITOR) {
                                /* If we are in the SE, and this road-piece has no town owner yet, it just found an
                                 * owner :) (happy happy happy road now) */
                                SetRoadOwner(tile, ROADTYPE_ROAD, OWNER_TOWN);
                                SetTownIndex(tile, t->index);
                        }
                }
        }

        return false;
}

/**
 * Generate a random road block.
 * The probability of a straight road
 * is somewhat higher than a curved.
 *
 * @return A RoadBits value with 2 bits set
 */
static RoadBits GenRandomRoadBits()
{
        uint32 r = Random();
        uint a = GB(r, 0, 2);
        uint b = GB(r, 8, 2);
        if (a == b) b ^= 2;
        return (RoadBits)((ROAD_NW << a) + (ROAD_NW << b));
}

/**
 * Grow the town
 * @param t town to grow
 * @return true iff a house was built
 */
static bool GrowTown(Town *t)
{
        static const CoordDiff _town_coord_mod[] = {
                {-1,  0},
                { 1,  1},
                { 1, -1},
                {-1, -1},
                {-1,  0},
                { 0,  2},
                { 2,  0},
                { 0, -2},
                {-1, -1},
                {-2,  2},
                { 2,  2},
                { 2, -2},
                { 0,  0}
        };

        /* Current "company" is a town */
        Backup<CompanyByte> cur_company(_current_company, OWNER_TOWN, FILE_LINE);

        TileIndex tile = t->xy; // The tile we are working with ATM

        /* Find a road that we can base the construction on. */
        const CoordDiff *ptr;
        for (ptr = _town_coord_mod; ptr != endof(_town_coord_mod); ++ptr) {
                if (GetTownRoadBits(tile) != ROAD_NONE) {
                        bool r = GrowTownFromTile (t, tile);
                        cur_company.Restore();
                        return r;
                }
                tile = TILE_ADD(tile, ToTileIndexDiff(*ptr));
        }

        /* No road available, try to build a random road block by
         * clearing some land and then building a road there. */
        if (_settings_game.economy.allow_town_roads || _generating_world) {
                tile = t->xy;
                for (ptr = _town_coord_mod; ptr != endof(_town_coord_mod); ++ptr) {
                        /* Only work with plain land that not already has a house */
                        if (!IsHouseTile(tile) && IsTileFlat(tile)) {
                                if (DoCommand(tile, 0, 0, DC_AUTO | DC_NO_WATER, CMD_LANDSCAPE_CLEAR).Succeeded()) {
                                        DoCommand(tile, GenRandomRoadBits(), t->index, DC_EXEC | DC_AUTO, CMD_BUILD_ROAD);
                                        cur_company.Restore();
                                        return true;
                                }
                        }
                        tile = TILE_ADD(tile, ToTileIndexDiff(*ptr));
                }
        }

        cur_company.Restore();
        return false;
}

void UpdateTownRadius(Town *t)
{
        static const uint32 _town_squared_town_zone_radius_data[23][5] = {
                {  4,  0,  0,  0,  0}, // 0
                { 16,  0,  0,  0,  0},
                { 25,  0,  0,  0,  0},
                { 36,  0,  0,  0,  0},
                { 49,  0,  4,  0,  0},
                { 64,  0,  4,  0,  0}, // 20
                { 64,  0,  9,  0,  1},
                { 64,  0,  9,  0,  4},
                { 64,  0, 16,  0,  4},
                { 81,  0, 16,  0,  4},
                { 81,  0, 16,  0,  4}, // 40
                { 81,  0, 25,  0,  9},
                { 81, 36, 25,  0,  9},
                { 81, 36, 25, 16,  9},
                { 81, 49,  0, 25,  9},
                { 81, 64,  0, 25,  9}, // 60
                { 81, 64,  0, 36,  9},
                { 81, 64,  0, 36, 16},
                {100, 81,  0, 49, 16},
                {100, 81,  0, 49, 25},
                {121, 81,  0, 49, 25}, // 80
                {121, 81,  0, 49, 25},
                {121, 81,  0, 49, 36}, // 88
        };

        if (t->cache.num_houses < 92) {
                memcpy(t->cache.squared_town_zone_radius, _town_squared_town_zone_radius_data[t->cache.num_houses / 4], sizeof(t->cache.squared_town_zone_radius));
        } else {
                int mass = t->cache.num_houses / 8;
                /* Actually we are proportional to sqrt() but that's right because we are covering an area.
                 * The offsets are to make sure the radii do not decrease in size when going from the table
                 * to the calculated value.*/
                t->cache.squared_town_zone_radius[0] = mass * 15 - 40;
                t->cache.squared_town_zone_radius[1] = mass * 9 - 15;
                t->cache.squared_town_zone_radius[2] = 0;
                t->cache.squared_town_zone_radius[3] = mass * 5 - 5;
                t->cache.squared_town_zone_radius[4] = mass * 3 + 5;
        }
}

void UpdateTownMaxPass(Town *t)
{
        t->supplied[CT_PASSENGERS].old_max = t->cache.population >> 3;
        t->supplied[CT_MAIL].old_max = t->cache.population >> 4;
}

/**
 * Town constructor.
 * @param tile Center tile of the town.
 * @param townnameparts Town name.
 * @param city Whether the town is a city.
 * @param layout Road layout of the town.
 */
Town::Town (TileIndex tile, uint32 townnameparts, bool city, TownLayout layout) :
        xy (tile), townnameparams (_settings_game.game_creation.town_name),
        townnameparts (townnameparts), name (NULL), flags (0),
        noise_reached (0), statues (0), have_ratings (0), text (NULL),
        time_until_rebuild (10), grow_counter (0), growth_rate (250),
        fund_buildings_months (0), larger_town (city)
{
        add_to_tileset();

        this->cache.num_houses = 0;
        this->cache.population = 0;
        UpdateTownRadius (this);

        this->exclusivity = INVALID_COMPANY;
        this->exclusive_counter = 0;

        for (uint i = 0; i != MAX_COMPANIES; i++) this->ratings[i] = RATING_INITIAL;

        /* Set the default cargo requirement for town growth */
        switch (_settings_game.game_creation.landscape) {
                case LT_ARCTIC:
                        if (FindFirstCargoWithTownEffect(TE_FOOD) != NULL) this->goal[TE_FOOD] = TOWN_GROWTH_WINTER;
                        break;

                case LT_TROPIC:
                        if (FindFirstCargoWithTownEffect(TE_FOOD) != NULL) this->goal[TE_FOOD] = TOWN_GROWTH_DESERT;
                        if (FindFirstCargoWithTownEffect(TE_WATER) != NULL) this->goal[TE_WATER] = TOWN_GROWTH_DESERT;
                        break;
        }

        this->layout = (layout != TL_RANDOM) ? layout :
                        (TownLayout) (TileHash (TileX(tile), TileY(tile)) % (NUM_TLS - 1));
}

/**
 * Does the actual town creation.
 * @param tile Where to put it
 * @param townnameparts The town name
 * @param size Parameter for size determination
 * @param city whether to build a city or town
 * @param layout the (road) layout of the town
 * @param manual was the town placed manually?
 * @return The created town
 */
static Town *DoCreateTown (TileIndex tile, uint32 townnameparts,
        TownSize size, bool city, TownLayout layout, bool manual)
{
        Town *t = new Town (tile, townnameparts, city, layout);

        int x = (int)size * 16 + 3;
        if (size == TSZ_RANDOM) x = (Random() & 0xF) + 8;
        /* Don't create huge cities when founding town in-game */
        if (city && (!manual || _game_mode == GM_EDITOR)) x *= _settings_game.economy.initial_city_size;

        t->cache.num_houses += x;
        UpdateTownRadius(t);

        int i = x * 4;
        do {
                GrowTown(t);
        } while (--i);

        t->cache.num_houses -= x;
        UpdateTownRadius(t);
        UpdateTownMaxPass(t);
        UpdateAirportsNoise();

        t->UpdateVirtCoord();
        InvalidateWindowData(WC_TOWN_DIRECTORY, 0, 0);
        InvalidateWindowData(WC_SELECT_TOWN, 0);

        return t;
}

/**
 * Checks if it's possible to place a town at given tile
 * @param tile tile to check
 * @return error string or STR_NULL on success
 */
static StringID TownCanBePlacedHere (TileIndex tile)
{
        /* Check if too close to the edge of map */
        if (DistanceFromEdge(tile) < 12) {
                return STR_ERROR_TOO_CLOSE_TO_EDGE_OF_MAP_SUB;
        }

        /* Check distance to all other towns. */
        if (Town::find_any<DistanceManhattan> (tile, 19)) {
                return STR_ERROR_TOO_CLOSE_TO_ANOTHER_TOWN;
        }

        /* Can only build on clear flat areas, possibly with trees. */
        if (!IsGroundTile(tile) || !IsTileFlat(tile)) {
                return STR_ERROR_SITE_UNSUITABLE;
        }

        return STR_NULL;
}

/**
 * Verifies this custom name is unique. Only custom names are checked.
 * @param name name to check
 * @return is this name unique?
 */
static bool IsUniqueTownName(const char *name)
{
        const Town *t;

        FOR_ALL_TOWNS(t) {
                if (t->name != NULL && strcmp(t->name, name) == 0) return false;
        }

        return true;
}

/**
 * Create a new town.
 * @param tile coordinates where town is built
 * @param flags type of operation
 * @param p1  0..1 size of the town (@see TownSize)
 *               2 true iff it should be a city
 *            3..5 town road layout (@see TownLayout)
 *               6 use random location (randomize \c tile )
 * @param p2 town name parts
 * @param text Custom name for the town. If empty, the town name parts will be used.
 * @return the cost of this operation or an error
 */
CommandCost CmdFoundTown(TileIndex tile, DoCommandFlag flags, uint32 p1, uint32 p2, const char *text)
{
        TownSize size = Extract<TownSize, 0, 2>(p1);
        bool city = HasBit(p1, 2);
        TownLayout layout = Extract<TownLayout, 3, 3>(p1);
        TownNameParams par(_settings_game.game_creation.town_name);
        bool random = HasBit(p1, 6);
        uint32 townnameparts = p2;

        if (size >= TSZ_END) return CMD_ERROR;
        if (layout >= NUM_TLS) return CMD_ERROR;

        /* Some things are allowed only in the scenario editor and for game scripts. */
        if (_game_mode != GM_EDITOR && _current_company != OWNER_DEITY) {
                if (_settings_game.economy.found_town == TF_FORBIDDEN) return CMD_ERROR;
                if (size == TSZ_LARGE) return CMD_ERROR;
                if (random) return CMD_ERROR;
                if (_settings_game.economy.found_town != TF_CUSTOM_LAYOUT && layout != _settings_game.economy.town_layout) {
                        return CMD_ERROR;
                }
        } else if (_current_company == OWNER_DEITY && random) {
                /* Random parameter is not allowed for Game Scripts. */
                return CMD_ERROR;
        }

        if (StrEmpty(text)) {
                /* If supplied name is empty, townnameparts has to generate unique automatic name */
                if (!VerifyTownName(townnameparts, &par)) return_cmd_error(STR_ERROR_NAME_MUST_BE_UNIQUE);
        } else {
                /* If name is not empty, it has to be unique custom name */
                if (Utf8StringLength(text) >= MAX_LENGTH_TOWN_NAME_CHARS) return CMD_ERROR;
                if (!IsUniqueTownName(text)) return_cmd_error(STR_ERROR_NAME_MUST_BE_UNIQUE);
        }

        /* Allocate town struct */
        if (!Town::CanAllocateItem()) return_cmd_error(STR_ERROR_TOO_MANY_TOWNS);

        if (!random) {
                StringID str = TownCanBePlacedHere (tile);
                if (str != STR_NULL) return_cmd_error(str);
        }

        static const byte price_mult[][TSZ_RANDOM + 1] = {{ 15, 25, 40, 25 }, { 20, 35, 55, 35 }};
        /* multidimensional arrays have to have defined length of non-first dimension */
        assert_compile(lengthof(price_mult[0]) == 4);

        CommandCost cost(EXPENSES_OTHER, _price[PR_BUILD_TOWN]);
        byte mult = price_mult[city][size];

        cost.MultiplyCost(mult);

        /* Create the town */
        if (flags & DC_EXEC) {
                if (cost.GetCost() > GetAvailableMoneyForCommand()) {
                        _additional_cash_required = cost.GetCost();
                        return CommandCost(EXPENSES_OTHER);
                }

                Backup<bool> old_generating_world(_generating_world, true, FILE_LINE);
                UpdateNearestTownForRoadTiles(true);
                Town *t;
                if (random) {
                        t = CreateRandomTown(20, townnameparts, size, city, layout);
                        if (t == NULL) {
                                cost = CommandCost(STR_ERROR_NO_SPACE_FOR_TOWN);
                        } else {
                                _new_town_id = t->index;
                        }
                } else {
                        t = DoCreateTown (tile, townnameparts, size, city, layout, true);
                }
                UpdateNearestTownForRoadTiles(false);
                old_generating_world.Restore();

                if (t != NULL && !StrEmpty(text)) {
                        t->name = xstrdup(text);
                        t->UpdateVirtCoord();
                }

                if (_game_mode != GM_EDITOR) {
                        /* 't' can't be NULL since 'random' is false outside scenedit */
                        assert(!random);

                        AddNewsItem<FoundTownNewsItem> (t->index, tile, _current_company);
                        AI::BroadcastNewEvent(new ScriptEventTownFounded(t->index));
                        Game::NewEvent(new ScriptEventTownFounded(t->index));
                }
        }
        return cost;
}

/**
 * Towns must all be placed on the same grid or when they eventually
 * interpenetrate their road networks will not mesh nicely; this
 * function adjusts a tile so that it aligns properly.
 *
 * @param tile the tile to start at
 * @param layout which town layout algo is in effect
 * @return the adjusted tile
 */
static TileIndex AlignTileToGrid(TileIndex tile, TownLayout layout)
{
        switch (layout) {
                case TL_2X2_GRID: return TileXY(TileX(tile) - TileX(tile) % 3, TileY(tile) - TileY(tile) % 3);
                case TL_3X3_GRID: return TileXY(TileX(tile) & ~3, TileY(tile) & ~3);
                default:          return tile;
        }
}

/**
 * Towns must all be placed on the same grid or when they eventually
 * interpenetrate their road networks will not mesh nicely; this
 * function tells you if a tile is properly aligned.
 *
 * @param tile the tile to start at
 * @param layout which town layout algo is in effect
 * @return true if the tile is in the correct location
 */
static bool IsTileAlignedToGrid(TileIndex tile, TownLayout layout)
{
        switch (layout) {
                case TL_2X2_GRID: return TileX(tile) % 3 == 0 && TileY(tile) % 3 == 0;
                case TL_3X3_GRID: return TileX(tile) % 4 == 0 && TileY(tile) % 4 == 0;
                default:          return true;
        }
}

/**
 * Given a spot on the map (presumed to be a water tile), find a good
 * coastal spot to build a city. We don't want to build too close to
 * the edge if we can help it (since that retards city growth) hence
 * the search within a search within a search. O(n*m^2), where n is
 * how far to search for land, and m is how far inland to look for a
 * flat spot.
 *
 * @param tile Start looking from this spot.
 * @param layout the road layout to search for
 * @return tile that was found
 */
static TileIndex FindNearestGoodCoastalTownSpot(TileIndex tile, TownLayout layout)
{
        CircularTileIterator iter (tile, 40);
        for (TileIndex coast = iter; coast != INVALID_TILE; coast = ++iter) {
                if (IsGroundTile (coast)) {
                        /* Search for a good inland spot for a town. */
                        TileIndex spot_tile = INVALID_TILE;
                        uint spot_dist = 0;

                        CircularTileIterator iter (coast, 10);
                        for (TileIndex t = iter; t != INVALID_TILE; t = ++iter) {
                                if (!IsGroundTile(t)) continue;
                                if (!IsTileFlat(t)) continue;
                                if (!IsTileAlignedToGrid (t, layout)) continue;

                                uint dist = GetClosestWaterDistance (t, true);
                                if (dist > spot_dist) {
                                        spot_tile = t;
                                        spot_dist = dist;
                                }
                        }
                        return spot_tile;
                }
        }

        /* if we get here just give up */
        return INVALID_TILE;
}

static Town *CreateRandomTown(uint attempts, uint32 townnameparts, TownSize size, bool city, TownLayout layout)
{
        assert(_game_mode == GM_EDITOR || _generating_world); // These are the preconditions for CMD_DELETE_TOWN

        if (!Town::CanAllocateItem()) return NULL;

        do {
                /* Generate a tile index not too close from the edge */
                TileIndex tile = AlignTileToGrid(RandomTile(), layout);

                /* if we tried to place the town on water, slide it over onto
                 * the nearest likely-looking spot */
                if (IsWaterTile(tile)) {
                        tile = FindNearestGoodCoastalTownSpot(tile, layout);
                        if (tile == INVALID_TILE) continue;
                }

                /* Make sure town can be placed here */
                if (TownCanBePlacedHere (tile) != STR_NULL) continue;

                /* Allocate a town struct */
                Town *t = DoCreateTown (tile, townnameparts, size, city, layout, false);

                /* if the population is still 0 at the point, then the
                 * placement is so bad it couldn't grow at all */
                if (t->cache.population > 0) return t;

                Backup<CompanyByte> cur_company(_current_company, OWNER_TOWN, FILE_LINE);
                CommandCost rc = DoCommand(t->xy, t->index, 0, DC_EXEC, CMD_DELETE_TOWN);
                cur_company.Restore();
                assert(rc.Succeeded());

                /* We already know that we can allocate a single town when
                 * entering this function. However, we create and delete
                 * a town which "resets" the allocation checks. As such we
                 * need to check again when assertions are enabled. */
                assert(Town::CanAllocateItem());
        } while (--attempts != 0);

        return NULL;
}

static const byte _num_initial_towns[4] = {5, 11, 23, 46};  // very low, low, normal, high

/**
 * This function will generate a certain amount of towns, with a certain layout
 * It can be called from the scenario editor (i.e.: generate Random Towns)
 * as well as from world creation.
 * @param layout which towns will be set to, when created
 * @return true if towns have been successfully created
 */
bool GenerateTowns(TownLayout layout)
{
        uint current_number = 0;
        uint difficulty = (_game_mode != GM_EDITOR) ? _settings_game.difficulty.number_towns : 0;
        uint total = (difficulty == (uint)CUSTOM_TOWN_NUMBER_DIFFICULTY) ? _settings_game.game_creation.custom_town_number : ScaleByMapSize(_num_initial_towns[difficulty] + (Random() & 7));
        total = min(Town::Pool::MAX_SIZE, total);
        uint32 townnameparts;
        TownNames town_names;

        SetGeneratingWorldProgress(GWP_TOWN, total);

        /* First attempt will be made at creating the suggested number of towns.
         * Note that this is really a suggested value, not a required one.
         * We would not like the system to lock up just because the user wanted 100 cities on a 64*64 map, would we? */
        do {
                bool city = (_settings_game.economy.larger_towns != 0 && Chance16(1, _settings_game.economy.larger_towns));
                IncreaseGeneratingWorldProgress(GWP_TOWN);
                /* Get a unique name for the town. */
                if (!GenerateTownName(&townnameparts, &town_names)) continue;
                /* try 20 times to create a random-sized town for the first loop. */
                if (CreateRandomTown(20, townnameparts, TSZ_RANDOM, city, layout) != NULL) current_number++; // If creation was successful, raise a flag.
        } while (--total);

        town_names.clear();

        if (current_number != 0) return true;

        /* If current_number is still zero at this point, it means that not a single town has been created.
         * So give it a last try, but now more aggressive */
        if (GenerateTownName(&townnameparts) &&
                        CreateRandomTown(10000, townnameparts, TSZ_RANDOM, _settings_game.economy.larger_towns != 0, layout) != NULL) {
                return true;
        }

        /* If there are no towns at all and we are generating new game, bail out */
        if (Town::GetNumItems() == 0 && _game_mode != GM_EDITOR) {
                ShowErrorMessage(STR_ERROR_COULD_NOT_CREATE_TOWN, INVALID_STRING_ID, WL_CRITICAL);
        }

        return false;  // we are still without a town? we failed, simply
}


/**
 * Returns the bit corresponding to the town zone of the specified tile
 * @param t Town on which town zone is to be found
 * @param tile TileIndex where town zone needs to be found
 * @return the bit position of the given zone, as defined in HouseZones
 */
HouseZonesBits GetTownRadiusGroup(const Town *t, TileIndex tile)
{
        uint dist = DistanceSquare(tile, t->xy);

        if (t->fund_buildings_months && dist <= 25) return HZB_TOWN_CENTRE;

        HouseZonesBits smallest = HZB_TOWN_EDGE;
        for (HouseZonesBits i = HZB_BEGIN; i < HZB_END; i++) {
                if (dist < t->cache.squared_town_zone_radius[i]) smallest = i;
        }

        return smallest;
}

/**
 * Clears tile and builds a house or house part.
 * @param tile tile index
 * @param t The town to clear the house for
 * @param counter of construction step
 * @param stage of construction (used for drawing)
 * @param type of house. Index into house specs array
 * @param random_bits required for newgrf houses
 * @pre house can be built here
 */
static inline void ClearMakeHouseTile(TileIndex tile, Town *t, byte counter, byte stage, HouseID type, byte random_bits)
{
        CommandCost cc = DoCommand(tile, 0, 0, DC_EXEC | DC_AUTO | DC_NO_WATER, CMD_LANDSCAPE_CLEAR);

        assert(cc.Succeeded());

        assert(IsGroundTile(tile));

        IncreaseBuildingCount(t, type);
        MakeHouseTile(tile, t->index, counter, stage, type, random_bits, HouseSpec::Get(type)->processing_time);
        if (HouseSpec::Get(type)->building_flags & BUILDING_IS_ANIMATED) AddAnimatedTile(tile);

        MarkTileDirtyByTile(tile);
}


/**
 * Write house information into the map. For houses > 1 tile, all tiles are marked.
 * @param t tile index
 * @param town The town related to this house
 * @param counter of construction step
 * @param stage of construction (used for drawing)
 * @param type of house. Index into house specs array
 * @param random_bits required for newgrf houses
 * @pre house can be built here
 */
static void MakeTownHouse(TileIndex t, Town *town, byte counter, byte stage, HouseID type, byte random_bits)
{
        BuildingFlags size = HouseSpec::Get(type)->building_flags;

        ClearMakeHouseTile(t, town, counter, stage, type, random_bits);
        if (size & BUILDING_2_TILES_Y)   ClearMakeHouseTile(t + TileDiffXY(0, 1), town, counter, stage, ++type, random_bits);
        if (size & BUILDING_2_TILES_X)   ClearMakeHouseTile(t + TileDiffXY(1, 0), town, counter, stage, ++type, random_bits);
        if (size & BUILDING_HAS_4_TILES) ClearMakeHouseTile(t + TileDiffXY(1, 1), town, counter, stage, ++type, random_bits);
}


/**
 * Checks if a house can be built here. Important is slope, bridge above
 * and ability to clear the land.
 * @param tile tile to check
 * @param noslope are slopes (foundations) allowed?
 * @return true iff house can be built here
 */
static inline bool CanBuildHouseHere(TileIndex tile, bool noslope)
{
        /* cannot build on these slopes... */
        Slope slope = GetTileSlope(tile);
        if ((noslope && slope != SLOPE_FLAT) || IsSteepSlope(slope)) return false;

        /* building under a bridge? */
        if (HasBridgeAbove(tile)) return false;

        /* can we clear the land? */
        return DoCommand(tile, 0, 0, DC_AUTO | DC_NO_WATER, CMD_LANDSCAPE_CLEAR).Succeeded();
}


/**
 * Checks if a house can be built at this tile, must have the same max z as parameter.
 * @param tile tile to check
 * @param z max z of this tile so more parts of a house are at the same height (with foundation)
 * @param noslope are slopes (foundations) allowed?
 * @return true iff house can be built here
 * @see CanBuildHouseHere()
 */
static inline bool CheckBuildHouseSameZ(TileIndex tile, int z, bool noslope)
{
        if (!CanBuildHouseHere(tile, noslope)) return false;

        /* if building on slopes is allowed, there will be flattening foundation (to tile max z) */
        if (GetTileMaxZ(tile) != z) return false;

        return true;
}


/**
 * Checks if a house of size 2x2 can be built at this tile
 * @param tile tile, N corner
 * @param z maximum tile z so all tile have the same max z
 * @param noslope are slopes (foundations) allowed?
 * @return true iff house can be built
 * @see CheckBuildHouseSameZ()
 */
static bool CheckFree2x2Area(TileIndex tile, int z, bool noslope)
{
        /* we need to check this tile too because we can be at different tile now */
        if (!CheckBuildHouseSameZ(tile, z, noslope)) return false;

        for (DiagDirection d = DIAGDIR_SE; d < DIAGDIR_END; d++) {
                tile += TileOffsByDiagDir(d);
                if (!CheckBuildHouseSameZ(tile, z, noslope)) return false;
        }

        return true;
}


/**
 * Checks if current town layout allows building here
 * @param t town
 * @param tile tile to check
 * @return true iff town layout allows building here
 * @note see layouts
 */
static inline bool TownLayoutAllowsHouseHere(Town *t, TileIndex tile)
{
        /* Allow towns everywhere when we don't build roads */
        if (!_settings_game.economy.allow_town_roads && !_generating_world) return true;

        CoordDiff grid_pos = TileCoordDiff(t->xy, tile);

        switch (t->layout) {
                case TL_2X2_GRID:
                        if ((grid_pos.x % 3) == 0 || (grid_pos.y % 3) == 0) return false;
                        break;

                case TL_3X3_GRID:
                        if ((grid_pos.x % 4) == 0 || (grid_pos.y % 4) == 0) return false;
                        break;

                default:
                        break;
        }

        return true;
}


/**
 * Checks if current town layout allows 2x2 building here
 * @param t town
 * @param tile tile to check
 * @return true iff town layout allows 2x2 building here
 * @note see layouts
 */
static inline bool TownLayoutAllows2x2HouseHere(Town *t, TileIndex tile)
{
        /* Allow towns everywhere when we don't build roads */
        if (!_settings_game.economy.allow_town_roads && !_generating_world) return true;

        /* Compute relative position of tile. (Positive offsets are towards north) */
        CoordDiff grid_pos = TileCoordDiff(t->xy, tile);

        switch (t->layout) {
                case TL_2X2_GRID:
                        grid_pos.x %= 3;
                        grid_pos.y %= 3;
                        if ((grid_pos.x != 2 && grid_pos.x != -1) ||
                                (grid_pos.y != 2 && grid_pos.y != -1)) return false;
                        break;

                case TL_3X3_GRID:
                        if ((grid_pos.x & 3) < 2 || (grid_pos.y & 3) < 2) return false;
                        break;

                default:
                        break;
        }

        return true;
}


/**
 * Checks if 1x2 or 2x1 building is allowed here, also takes into account current town layout
 * Also, tests both building positions that occupy this tile
 * @param tile tile where the building should be built
 * @param t town
 * @param maxz all tiles should have the same height
 * @param noslope are slopes forbidden?
 * @param second diagdir from first tile to second tile
 */
static bool CheckTownBuild2House(TileIndex *tile, Town *t, int maxz, bool noslope, DiagDirection second)
{
        /* 'tile' is already checked in BuildTownHouse() - CanBuildHouseHere() and slope test */

        TileIndex tile2 = *tile + TileOffsByDiagDir(second);
        if (TownLayoutAllowsHouseHere(t, tile2) && CheckBuildHouseSameZ(tile2, maxz, noslope)) return true;

        tile2 = *tile + TileOffsByDiagDir(ReverseDiagDir(second));
        if (TownLayoutAllowsHouseHere(t, tile2) && CheckBuildHouseSameZ(tile2, maxz, noslope)) {
                *tile = tile2;
                return true;
        }

        return false;
}


/**
 * Checks if 2x2 building is allowed here, also takes into account current town layout
 * Also, tests all four building positions that occupy this tile
 * @param tile tile where the building should be built
 * @param t town
 * @param maxz all tiles should have the same height
 * @param noslope are slopes forbidden?
 */
static bool CheckTownBuild2x2House(TileIndex *tile, Town *t, int maxz, bool noslope)
{
        TileIndex tile2 = *tile;

        for (DiagDirection d = DIAGDIR_SE;; d++) { // 'd' goes through DIAGDIR_SE, DIAGDIR_SW, DIAGDIR_NW, DIAGDIR_END
                if (TownLayoutAllows2x2HouseHere(t, tile2) && CheckFree2x2Area(tile2, maxz, noslope)) {
                        *tile = tile2;
                        return true;
                }
                if (d == DIAGDIR_END) break;
                tile2 += TileOffsByDiagDir(ReverseDiagDir(d)); // go clockwise
        }

        return false;
}

/** Get the flag to test/set for building uniqueness in a town. */
static uint GetHouseUniqueFlags (const HouseSpec *hs)
{
        return  (hs->building_flags & BUILDING_IS_CHURCH)  ? (1 << TOWN_HAS_CHURCH)  :
                (hs->building_flags & BUILDING_IS_STADIUM) ? (1 << TOWN_HAS_STADIUM) :
                0;
}

/**
 * Check if a town can have a new house of a given type.
 * @param t The town to check.
 * @param house The house type that we want to add.
 * @param STR_NULL on success, else an error message.
 */
StringID IsNewTownHouseAllowed (const Town *t, HouseID house)
{
        const HouseSpec *hs = HouseSpec::Get(house);

        /* Don't let these counters overflow. Global counters are 32bit, there will never be that many houses. */
        if (hs->class_id != HOUSE_NO_CLASS) {
                /* id_count is always <= class_count, so it doesn't need to be checked. */
                if (t->cache.building_counts.class_count[hs->class_id] == UINT16_MAX) {
                        return STR_ERROR_TOO_MANY_CLASS_HOUSES;
                }
        } else {
                /* If the house has no class, check id_count instead. */
                if (t->cache.building_counts.id_count[house] == UINT16_MAX) {
                        return STR_ERROR_TOO_MANY_HOUSES;
                }
        }

        /* Special houses that there can be only one of. */
        uint oneof = GetHouseUniqueFlags (hs);
        if (t->flags & oneof) return STR_ERROR_ONLY_ONE_BUILDING_PER_TOWN;

        return STR_NULL;
}

/**
 * Really build a house.
 * @param t town to build house in
 * @param tile house location
 * @param house house type
 * @param random_bits random bits for the house
 */
void DoBuildHouse(Town *t, TileIndex tile, HouseID house, byte random_bits)
{
        t->cache.num_houses++;

        const HouseSpec *hs = HouseSpec::Get(house);

        /* Special houses that there can be only one of. */
        uint oneof = GetHouseUniqueFlags (hs);
        assert ((t->flags & oneof) == 0);
        t->flags |= oneof;

        byte construction_counter = 0;
        byte construction_stage = 0;

        if (_generating_world || _game_mode == GM_EDITOR) {
                uint32 r = Random();

                construction_stage = TOWN_HOUSE_COMPLETED;
                if (Chance16(1, 7)) construction_stage = GB(r, 0, 2);

                if (construction_stage == TOWN_HOUSE_COMPLETED) {
                        ChangePopulation(t, hs->population);
                } else {
                        construction_counter = GB(r, 2, 2);
                }
        }

        MakeTownHouse(tile, t, construction_counter, construction_stage, house, random_bits);
        UpdateTownRadius(t);
        UpdateTownCargoes(t, tile);
}

/**
 * Tries to build a house at this tile
 * @param t town the house will belong to
 * @param tile where the house will be built
 * @return false iff no house can be built at this tile
 */
static bool BuildTownHouse(Town *t, TileIndex tile)
{
        /* forbidden building here by town layout */
        if (!TownLayoutAllowsHouseHere(t, tile)) return false;

        /* no house allowed at all, bail out */
        if (!CanBuildHouseHere(tile, false)) return false;

        Slope slope = GetTileSlope(tile);
        int maxz = GetTileMaxZ(tile);

        /* Get the town zone type of the current tile, as well as the climate.
         * This will allow to easily compare with the specs of the new house to build */
        HouseZonesBits rad = GetTownRadiusGroup(t, tile);

        /* Above snow? */
        int land = _settings_game.game_creation.landscape;
        if (land == LT_ARCTIC && maxz > HighestSnowLine()) land = -1;

        uint bitmask = (1 << rad) + (1 << (land + 12));

        /* bits 0-4 are used
         * bits 11-15 are used
         * bits 5-10 are not used. */
        HouseID houses[NUM_HOUSES];
        uint num = 0;
        uint probs[NUM_HOUSES];
        uint probability_max = 0;

        /* Generate a list of all possible houses that can be built. */
        for (uint i = 0; i < NUM_HOUSES; i++) {
                const HouseSpec *hs = HouseSpec::Get(i);

                /* Verify that the candidate house spec matches the current tile status */
                if ((~hs->building_availability & bitmask) != 0 || !hs->enabled || hs->grf_prop.override != INVALID_HOUSE_ID) continue;

                if (IsNewTownHouseAllowed (t, i) != STR_NULL) continue;

                /* Without NewHouses, all houses have probability '1' */
                uint cur_prob = (_loaded_newgrf_features.has_newhouses ? hs->probability : 1);
                probability_max += cur_prob;
                probs[num] = cur_prob;
                houses[num++] = (HouseID)i;
        }

        TileIndex baseTile = tile;

        while (probability_max > 0) {
                /* Building a multitile building can change the location of tile.
                 * The building would still be built partially on that tile, but
                 * its northern tile would be elsewhere. However, if the callback
                 * fails we would be basing further work from the changed tile.
                 * So a next 1x1 tile building could be built on the wrong tile. */
                tile = baseTile;

                uint r = RandomRange(probability_max);
                uint i;
                for (i = 0; i < num; i++) {
                        if (probs[i] > r) break;
                        r -= probs[i];
                }

                HouseID house = houses[i];
                probability_max -= probs[i];

                /* remove tested house from the set */
                num--;
                houses[i] = houses[num];
                probs[i] = probs[num];

                const HouseSpec *hs = HouseSpec::Get(house);

                if (_loaded_newgrf_features.has_newhouses && !_generating_world &&
                                _game_mode != GM_EDITOR && (hs->extra_flags & BUILDING_IS_HISTORICAL) != 0) {
                        continue;
                }

                if (_cur_year < hs->min_year || _cur_year > hs->max_year) continue;

                /* Make sure there is no slope? */
                bool noslope = (hs->building_flags & TILE_NOT_SLOPED) != 0;
                if (noslope && slope != SLOPE_FLAT) continue;

                if (hs->building_flags & TILE_SIZE_2x2) {
                        if (!CheckTownBuild2x2House(&tile, t, maxz, noslope)) continue;
                } else if (hs->building_flags & TILE_SIZE_2x1) {
                        if (!CheckTownBuild2House(&tile, t, maxz, noslope, DIAGDIR_SW)) continue;
                } else if (hs->building_flags & TILE_SIZE_1x2) {
                        if (!CheckTownBuild2House(&tile, t, maxz, noslope, DIAGDIR_SE)) continue;
                } else {
                        /* 1x1 house checks are already done */
                }

                byte random_bits = Random();

                if (HasBit(hs->callback_mask, CBM_HOUSE_ALLOW_CONSTRUCTION)) {
                        uint16 callback_res = GetHouseCallback(CBID_HOUSE_ALLOW_CONSTRUCTION, 0, 0, house, t, tile, true, random_bits);
                        if (callback_res != CALLBACK_FAILED && !Convert8bitBooleanCallback(hs->grf_prop.grffile, CBID_HOUSE_ALLOW_CONSTRUCTION, callback_res)) continue;
                }

                DoBuildHouse(t, tile, house, random_bits);
                return true;
        }

        return false;
}

/**
 * Update data structures when a house is removed
 * @param tile  Tile of the house
 * @param t     Town owning the house
 * @param house House type
 */
static void DoClearTownHouseHelper(TileIndex tile, Town *t, HouseID house)
{
        assert(IsHouseTile(tile));
        DecreaseBuildingCount(t, house);
        DoClearSquare(tile);
        DeleteAnimatedTile(tile);

        DeleteNewGRFInspectWindow(GSF_HOUSES, tile);
}

/**
 * Determines if a given HouseID is part of a multitile house.
 * The given ID is set to the ID of the north tile and the TileDiff to the north tile is returned.
 *
 * @param house Is changed to the HouseID of the north tile of the same house
 * @return TileDiff from the tile of the given HouseID to the north tile
 */
TileIndexDiff GetHouseNorthPart(HouseID &house)
{
        if (house >= 3) { // house id 0,1,2 MUST be single tile houses, or this code breaks.
                if (HouseSpec::Get(house - 1)->building_flags & TILE_SIZE_2x1) {
                        house--;
                        return TileDiffXY(-1, 0);
                } else if (HouseSpec::Get(house - 1)->building_flags & BUILDING_2_TILES_Y) {
                        house--;
                        return TileDiffXY(0, -1);
                } else if (HouseSpec::Get(house - 2)->building_flags & BUILDING_HAS_4_TILES) {
                        house -= 2;
                        return TileDiffXY(-1, 0);
                } else if (HouseSpec::Get(house - 3)->building_flags & BUILDING_HAS_4_TILES) {
                        house -= 3;
                        return TileDiffXY(-1, -1);
                }
        }
        return 0;
}

void ClearTownHouse(Town *t, TileIndex tile)
{
        assert(IsHouseTile(tile));

        HouseID house = GetHouseType(tile);

        /* need to align the tile to point to the upper left corner of the house */
        tile += GetHouseNorthPart(house); // modifies house to the ID of the north tile

        const HouseSpec *hs = HouseSpec::Get(house);

        /* Remove population from the town if the house is finished. */
        if (IsHouseCompleted(tile)) {
                ChangePopulation(t, -hs->population);
        }

        t->cache.num_houses--;

        /* Clear flags for houses that only may exist once/town. */
        if (hs->building_flags & BUILDING_IS_CHURCH) {
                ClrBit(t->flags, TOWN_HAS_CHURCH);
        } else if (hs->building_flags & BUILDING_IS_STADIUM) {
                ClrBit(t->flags, TOWN_HAS_STADIUM);
        }

        /* Do the actual clearing of tiles */
        uint eflags = hs->building_flags;
        DoClearTownHouseHelper(tile, t, house);
        if (eflags & BUILDING_2_TILES_Y)   DoClearTownHouseHelper(tile + TileDiffXY(0, 1), t, ++house);
        if (eflags & BUILDING_2_TILES_X)   DoClearTownHouseHelper(tile + TileDiffXY(1, 0), t, ++house);
        if (eflags & BUILDING_HAS_4_TILES) DoClearTownHouseHelper(tile + TileDiffXY(1, 1), t, ++house);

        UpdateTownRadius(t);

        /* Update cargo acceptance. */
        UpdateTownCargoes(t, tile);
}

/**
 * Rename a town (server-only).
 * @param tile unused
 * @param flags type of operation
 * @param p1 town ID to rename
 * @param p2 unused
 * @param text the new name or an empty string when resetting to the default
 * @return the cost of this operation or an error
 */
CommandCost CmdRenameTown(TileIndex tile, DoCommandFlag flags, uint32 p1, uint32 p2, const char *text)
{
        Town *t = Town::GetIfValid(p1);
        if (t == NULL) return CMD_ERROR;

        bool reset = StrEmpty(text);

        if (!reset) {
                if (Utf8StringLength(text) >= MAX_LENGTH_TOWN_NAME_CHARS) return CMD_ERROR;
                if (!IsUniqueTownName(text)) return_cmd_error(STR_ERROR_NAME_MUST_BE_UNIQUE);
        }

        if (flags & DC_EXEC) {
                free(t->name);
                t->name = reset ? NULL : xstrdup(text);

                t->UpdateVirtCoord();
                InvalidateWindowData(WC_TOWN_DIRECTORY, 0, 1);
                SetWindowDirty(WC_SELECT_TOWN, 0);
                UpdateAllStationVirtCoords();
        }
        return CommandCost();
}

/**
 * Determines the first cargo with a certain town effect
 * @param effect Town effect of interest
 * @return first active cargo slot with that effect
 */
const CargoSpec *FindFirstCargoWithTownEffect(TownEffect effect)
{
        const CargoSpec *cs;
        FOR_ALL_CARGOSPECS(cs) {
                if (cs->town_effect == effect) return cs;
        }
        return NULL;
}

static void UpdateTownGrowRate(Town *t);

/**
 * Change the cargo goal of a town.
 * @param tile Unused.
 * @param flags Type of operation.
 * @param p1 various bitstuffed elements
 * - p1 = (bit  0 - 15) - Town ID to cargo game of.
 * - p1 = (bit 16 - 23) - TownEffect to change the game of.
 * @param p2 The new goal value.
 * @param text Unused.
 * @return Empty cost or an error.
 */
CommandCost CmdTownCargoGoal(TileIndex tile, DoCommandFlag flags, uint32 p1, uint32 p2, const char *text)
{
        if (_current_company != OWNER_DEITY) return CMD_ERROR;

        TownEffect te = (TownEffect)GB(p1, 16, 8);
        if (te < TE_BEGIN || te >= TE_END) return CMD_ERROR;

        uint16 index = GB(p1, 0, 16);
        Town *t = Town::GetIfValid(index);
        if (t == NULL) return CMD_ERROR;

        /* Validate if there is a cargo which is the requested TownEffect */
        const CargoSpec *cargo = FindFirstCargoWithTownEffect(te);
        if (cargo == NULL) return CMD_ERROR;

        if (flags & DC_EXEC) {
                t->goal[te] = p2;
                UpdateTownGrowRate(t);
                InvalidateWindowData(WC_TOWN_VIEW, index);
        }

        return CommandCost();
}

/**
 * Set a custom text in the Town window.
 * @param tile Unused.
 * @param flags Type of operation.
 * @param p1 Town ID to change the text of.
 * @param p2 Unused.
 * @param text The new text (empty to remove the text).
 * @return Empty cost or an error.
 */
CommandCost CmdTownSetText(TileIndex tile, DoCommandFlag flags, uint32 p1, uint32 p2, const char *text)
{
        if (_current_company != OWNER_DEITY) return CMD_ERROR;
        Town *t = Town::GetIfValid(p1);
        if (t == NULL) return CMD_ERROR;

        if (flags & DC_EXEC) {
                free(t->text);
                t->text = StrEmpty(text) ? NULL : xstrdup(text);
                InvalidateWindowData(WC_TOWN_VIEW, p1);
        }

        return CommandCost();
}

/**
 * Change the growth rate of the town.
 * @param tile Unused.
 * @param flags Type of operation.
 * @param p1 Town ID to cargo game of.
 * @param p2 Amount of days between growth, or TOWN_GROW_RATE_CUSTOM_NONE, or 0 to reset custom growth rate.
 * @param text Unused.
 * @return Empty cost or an error.
 */
CommandCost CmdTownGrowthRate(TileIndex tile, DoCommandFlag flags, uint32 p1, uint32 p2, const char *text)
{
        if (_current_company != OWNER_DEITY) return CMD_ERROR;
        if ((p2 & TOWN_GROW_RATE_CUSTOM) != 0 && p2 != TOWN_GROW_RATE_CUSTOM_NONE) return CMD_ERROR;
        if (GB(p2, 16, 16) != 0) return CMD_ERROR;

        Town *t = Town::GetIfValid(p1);
        if (t == NULL) return CMD_ERROR;

        if (flags & DC_EXEC) {
                if (p2 == 0) {
                        /* Clear TOWN_GROW_RATE_CUSTOM, UpdateTownGrowRate will determine a proper value */
                        t->growth_rate = 0;
                } else {
                        uint old_rate = t->growth_rate & ~TOWN_GROW_RATE_CUSTOM;
                        if (t->grow_counter >= old_rate) {
                                /* This also catches old_rate == 0 */
                                t->grow_counter = p2;
                        } else {
                                /* Scale grow_counter, so half finished houses stay half finished */
                                t->grow_counter = t->grow_counter * p2 / old_rate;
                        }
                        t->growth_rate = p2 | TOWN_GROW_RATE_CUSTOM;
                }
                UpdateTownGrowRate(t);
                InvalidateWindowData(WC_TOWN_VIEW, p1);
        }

        return CommandCost();
}

/**
 * Expand a town (scenario editor only).
 * @param tile Unused.
 * @param flags Type of operation.
 * @param p1 Town ID to expand.
 * @param p2 Amount to grow, or 0 to grow a random size up to the current amount of houses.
 * @param text Unused.
 * @return Empty cost or an error.
 */
CommandCost CmdExpandTown(TileIndex tile, DoCommandFlag flags, uint32 p1, uint32 p2, const char *text)
{
        if (_game_mode != GM_EDITOR && _current_company != OWNER_DEITY) return CMD_ERROR;
        Town *t = Town::GetIfValid(p1);
        if (t == NULL) return CMD_ERROR;

        if (flags & DC_EXEC) {
                /* The more houses, the faster we grow */
                if (p2 == 0) {
                        uint amount = RandomRange(ClampToU16(t->cache.num_houses / 10)) + 3;
                        t->cache.num_houses += amount;
                        UpdateTownRadius(t);

                        uint n = amount * 10;
                        do GrowTown(t); while (--n);

                        t->cache.num_houses -= amount;
                } else {
                        for (; p2 > 0; p2--) {
                                /* Try several times to grow, as we are really suppose to grow */
                                for (uint i = 0; i < 25; i++) if (GrowTown(t)) break;
                        }
                }
                UpdateTownRadius(t);

                UpdateTownMaxPass(t);
        }

        return CommandCost();
}

/**
 * Delete a town (scenario editor or worldgen only).
 * @param tile Unused.
 * @param flags Type of operation.
 * @param p1 Town ID to delete.
 * @param p2 Unused.
 * @param text Unused.
 * @return Empty cost or an error.
 */
CommandCost CmdDeleteTown(TileIndex tile, DoCommandFlag flags, uint32 p1, uint32 p2, const char *text)
{
        if (_game_mode != GM_EDITOR && !_generating_world) return CMD_ERROR;
        Town *t = Town::GetIfValid(p1);
        if (t == NULL) return CMD_ERROR;

        /* Stations refer to towns. */
        const Station *st;
        FOR_ALL_STATIONS(st) {
                if (st->town == t) {
                        /* Non-oil rig stations are always a problem. */
                        if (!(st->facilities & FACIL_AIRPORT) || st->airport.type != AT_OILRIG) return CMD_ERROR;
                        /* We can only automatically delete oil rigs *if* there's no vehicle on them. */
                        CommandCost ret = DoCommand(st->airport.tile, 0, 0, flags, CMD_LANDSCAPE_CLEAR);
                        if (ret.Failed()) return ret;
                }
        }

        /* Depots refer to towns. */
        const Depot *d;
        FOR_ALL_DEPOTS(d) {
                if (d->town == t) return CMD_ERROR;
        }

        /* Check all tiles for town ownership. */
        for (TileIndex tile = 0; tile < MapSize(); ++tile) {
                bool try_clear = false;
                if (IsHouseTile(tile)) {
                        try_clear = GetTownIndex(tile) == t->index;
                } else if (IsIndustryTile(tile)) {
                        try_clear = Industry::GetByTile(tile)->town == t;
                } else {
                        switch (GetTileType(tile)) {
                                case TT_MISC:
                                        if (IsTunnelTile(tile)) {
                                                try_clear = IsTileOwner(tile, OWNER_TOWN) && ClosestTownFromTile(tile) == t;
                                                break;
                                        }
                                        if (!IsLevelCrossingTile(tile)) break;
                                        /* fall through */
                                case TT_ROAD:
                                        try_clear = HasTownOwnedRoad(tile) && GetTownIndex(tile) == t->index;
                                        break;

                                case TT_OBJECT:
                                        if (Town::GetNumItems() == 1) {
                                                /* No towns will be left, remove it! */
                                                try_clear = true;
                                        } else {
                                                Object *o = Object::GetByTile(tile);
                                                if (o->town == t) {
                                                        if (o->type == OBJECT_STATUE) {
                                                                /* Statue... always remove. */
                                                                try_clear = true;
                                                        } else {
                                                                /* Tell to find a new town. */
                                                                if (flags & DC_EXEC) o->town = NULL;
                                                        }
                                                }
                                        }
                                        break;

                                default:
                                        break;
                        }
                }
                if (try_clear) {
                        CommandCost ret = DoCommand(tile, 0, 0, flags, CMD_LANDSCAPE_CLEAR);
                        if (ret.Failed()) return ret;
                }
        }

        /* The town destructor will delete the other things related to the town. */
        if (flags & DC_EXEC) delete t;

        return CommandCost();
}

/**
 * Factor in the cost of each town action.
 * @see TownActions
 */
const byte _town_action_costs[TACT_COUNT] = {
        2, 4, 9, 35, 48, 53, 117, 175
};

static CommandCost TownActionAdvertiseSmall(Town *t, DoCommandFlag flags)
{
        if (flags & DC_EXEC) {
                ModifyStationRatingAround(t->xy, _current_company, 0x40, 10);
        }
        return CommandCost();
}

static CommandCost TownActionAdvertiseMedium(Town *t, DoCommandFlag flags)
{
        if (flags & DC_EXEC) {
                ModifyStationRatingAround(t->xy, _current_company, 0x70, 15);
        }
        return CommandCost();
}

static CommandCost TownActionAdvertiseLarge(Town *t, DoCommandFlag flags)
{
        if (flags & DC_EXEC) {
                ModifyStationRatingAround(t->xy, _current_company, 0xA0, 20);
        }
        return CommandCost();
}

static CommandCost TownActionRoadRebuild(Town *t, DoCommandFlag flags)
{
        /* Check if the company is allowed to fund new roads. */
        if (!_settings_game.economy.fund_roads) return CMD_ERROR;

        if (flags & DC_EXEC) {
                t->road_build_months = 6;

                AddNewsItem<RoadRebuildNewsItem> (t->index, _current_company);
                AI::BroadcastNewEvent(new ScriptEventRoadReconstruction((ScriptCompany::CompanyID)(Owner)_current_company, t->index));
                Game::NewEvent(new ScriptEventRoadReconstruction((ScriptCompany::CompanyID)(Owner)_current_company, t->index));
        }
        return CommandCost();
}

/**
 * Check whether the land can be cleared.
 * @param tile Tile to check.
 * @return The tile can be cleared.
 */
static bool TryClearTile(TileIndex tile)
{
        Backup<CompanyByte> cur_company(_current_company, OWNER_NONE, FILE_LINE);
        CommandCost r = DoCommand(tile, 0, 0, DC_NONE, CMD_LANDSCAPE_CLEAR);
        cur_company.Restore();
        return r.Succeeded();
}

/**
 * Perform a 9x9 tiles circular search from the center of the town
 * in order to find a free tile to place a statue
 * @param t town to search in
 * @param flags Used to check if the statue must be built or not.
 * @return Empty cost or an error.
 */
static CommandCost TownActionBuildStatue(Town *t, DoCommandFlag flags)
{
        static const uint STATUE_NUMBER_INNER_TILES = 25; // Number of tiles in the center of the city where we try to protect houses.

        if (!Object::CanAllocateItem()) return_cmd_error(STR_ERROR_TOO_MANY_OBJECTS);

        TileIndex statue_tile = INVALID_TILE;
        uint tile_count = 0;
        CircularTileIterator iter (t->xy, 9);
        for (TileIndex tile = iter; tile != INVALID_TILE; tile = ++iter) {
                tile_count++;

                /* Statues can be build on slopes, just like houses. Only the steep slopes is a no go. */
                if (IsSteepSlope(GetTileSlope(tile))) continue;
                /* Don't build statues under bridges. */
                if (HasBridgeAbove(tile)) continue;

                /* A clear-able open space is always preferred. */
                if (IsGroundTile(tile) && TryClearTile(tile)) {
                        statue_tile = tile;
                        break;
                }

                bool house = IsHouseTile(tile);

                if (tile_count <= STATUE_NUMBER_INNER_TILES) {
                        /* Searching inside the inner circle; store first house. */
                        if (house && statue_tile == INVALID_TILE && TryClearTile(tile)) {
                                statue_tile = tile;
                        }

                        /* If we have reached the end of the inner circle, and have a saved house, terminate the search. */
                        if (tile_count == STATUE_NUMBER_INNER_TILES && statue_tile != INVALID_TILE) break;
                } else {
                        /* Searching outside the circle, just pick the first possible spot. */
                        if (house && TryClearTile(tile)) {
                                statue_tile = tile;
                                break;
                        }
                }
        }
        if (statue_tile == INVALID_TILE) return_cmd_error(STR_ERROR_STATUE_NO_SUITABLE_PLACE);

        if (flags & DC_EXEC) {
                Backup<CompanyByte> cur_company(_current_company, OWNER_NONE, FILE_LINE);
                DoCommand(statue_tile, 0, 0, DC_EXEC, CMD_LANDSCAPE_CLEAR);
                cur_company.Restore();
                BuildObject(OBJECT_STATUE, statue_tile, _current_company, t);
                SetBit(t->statues, _current_company); // Once found and built, "inform" the Town.
                MarkTileDirtyByTile(statue_tile);
        }
        return CommandCost();
}

static CommandCost TownActionFundBuildings(Town *t, DoCommandFlag flags)
{
        /* Check if it's allowed to buy the rights */
        if (!_settings_game.economy.fund_buildings) return CMD_ERROR;

        if (flags & DC_EXEC) {
                /* Build next tick */
                t->grow_counter = 1;
                /* And grow for 3 months */
                t->fund_buildings_months = 3;

                /* Enable growth (also checking GameScript's opinion) */
                UpdateTownGrowRate(t);

                SetWindowDirty(WC_TOWN_VIEW, t->index);
        }
        return CommandCost();
}

static CommandCost TownActionBuyRights(Town *t, DoCommandFlag flags)
{
        /* Check if it's allowed to buy the rights */
        if (!_settings_game.economy.exclusive_rights) return CMD_ERROR;

        if (flags & DC_EXEC) {
                t->exclusive_counter = 12;
                t->exclusivity = _current_company;

                ModifyStationRatingAround(t->xy, _current_company, 130, 17);

                SetWindowClassesDirty(WC_STATION_VIEW);

                /* Spawn news message */
                AddNewsItem<ExclusiveRightsNewsItem> (t->index, Company::Get(_current_company));
                AI::BroadcastNewEvent(new ScriptEventExclusiveTransportRights((ScriptCompany::CompanyID)(Owner)_current_company, t->index));
                Game::NewEvent(new ScriptEventExclusiveTransportRights((ScriptCompany::CompanyID)(Owner)_current_company, t->index));
        }
        return CommandCost();
}

static CommandCost TownActionBribe(Town *t, DoCommandFlag flags)
{
        if (flags & DC_EXEC) {
                if (Chance16(1, 14)) {
                        /* set as unwanted for 6 months */
                        t->unwanted[_current_company] = 6;

                        /* set all close by station ratings to 0 */
                        Station *st;
                        FOR_ALL_STATIONS(st) {
                                if (st->town == t && st->owner == _current_company) {
                                        for (CargoID i = 0; i < NUM_CARGO; i++) st->goods[i].rating = 0;
                                }
                        }

                        /* only show error message to the executing player. All errors are handled command.c
                         * but this is special, because it can only 'fail' on a DC_EXEC */
                        if (IsLocalCompany()) ShowErrorMessage(STR_ERROR_BRIBE_FAILED, INVALID_STRING_ID, WL_INFO);

                        /* decrease by a lot!
                         * ChangeTownRating is only for stuff in demolishing. Bribe failure should
                         * be independent of any cheat settings
                         */
                        if (t->ratings[_current_company] > RATING_BRIBE_DOWN_TO) {
                                t->ratings[_current_company] = RATING_BRIBE_DOWN_TO;
                                SetWindowDirty(WC_TOWN_AUTHORITY, t->index);
                        }
                } else {
                        ChangeTownRating(t, RATING_BRIBE_UP_STEP, RATING_BRIBE_MAXIMUM, DC_EXEC);
                }
        }
        return CommandCost();
}

typedef CommandCost TownActionProc(Town *t, DoCommandFlag flags);
static TownActionProc * const _town_action_proc[] = {
        TownActionAdvertiseSmall,
        TownActionAdvertiseMedium,
        TownActionAdvertiseLarge,
        TownActionRoadRebuild,
        TownActionBuildStatue,
        TownActionFundBuildings,
        TownActionBuyRights,
        TownActionBribe
};

/**
 * Get a list of available actions to do at a town.
 * @param nump if not NULL add put the number of available actions in it
 * @param cid the company that is querying the town
 * @param t the town that is queried
 * @return bitmasked value of enabled actions
 */
uint GetMaskOfTownActions(int *nump, CompanyID cid, const Town *t)
{
        int num = 0;
        TownActions buttons = TACT_NONE;

        /* Spectators and unwanted have no options */
        if (cid != COMPANY_SPECTATOR && !(_settings_game.economy.bribe && t->unwanted[cid])) {

                /* Things worth more than this are not shown */
                Money avail = Company::Get(cid)->money + _price[PR_STATION_VALUE] * 200;

                /* Check the action bits for validity and
                 * if they are valid add them */
                for (uint i = 0; i != lengthof(_town_action_costs); i++) {
                        const TownActions cur = (TownActions)(1 << i);

                        /* Is the company not able to bribe ? */
                        if (cur == TACT_BRIBE && (!_settings_game.economy.bribe || t->ratings[cid] >= RATING_BRIBE_MAXIMUM)) continue;

                        /* Is the company not able to buy exclusive rights ? */
                        if (cur == TACT_BUY_RIGHTS && !_settings_game.economy.exclusive_rights) continue;

                        /* Is the company not able to fund buildings ? */
                        if (cur == TACT_FUND_BUILDINGS && !_settings_game.economy.fund_buildings) continue;

                        /* Is the company not able to fund local road reconstruction? */
                        if (cur == TACT_ROAD_REBUILD && !_settings_game.economy.fund_roads) continue;

                        /* Is the company not able to build a statue ? */
                        if (cur == TACT_BUILD_STATUE && HasBit(t->statues, cid)) continue;

                        if (avail >= _town_action_costs[i] * _price[PR_TOWN_ACTION] >> 8) {
                                buttons |= cur;
                                num++;
                        }
                }
        }

        if (nump != NULL) *nump = num;
        return buttons;
}

/**
 * Do a town action.
 * This performs an action such as advertising, building a statue, funding buildings,
 * but also bribing the town-council
 * @param tile unused
 * @param flags type of operation
 * @param p1 town to do the action at
 * @param p2 action to perform, @see _town_action_proc for the list of available actions
 * @param text unused
 * @return the cost of this operation or an error
 */
CommandCost CmdDoTownAction(TileIndex tile, DoCommandFlag flags, uint32 p1, uint32 p2, const char *text)
{
        Town *t = Town::GetIfValid(p1);
        if (t == NULL || p2 >= lengthof(_town_action_proc)) return CMD_ERROR;

        if (!HasBit(GetMaskOfTownActions(NULL, _current_company, t), p2)) return CMD_ERROR;

        CommandCost cost(EXPENSES_OTHER, _price[PR_TOWN_ACTION] * _town_action_costs[p2] >> 8);

        CommandCost ret = _town_action_proc[p2](t, flags);
        if (ret.Failed()) return ret;

        if (flags & DC_EXEC) {
                SetWindowDirty(WC_TOWN_AUTHORITY, p1);
        }

        return cost;
}

static void UpdateTownRating(Town *t)
{
        /* Increase company ratings if they're low */
        const Company *c;
        FOR_ALL_COMPANIES(c) {
                if (t->ratings[c->index] < RATING_GROWTH_MAXIMUM) {
                        t->ratings[c->index] = min((int)RATING_GROWTH_MAXIMUM, t->ratings[c->index] + RATING_GROWTH_UP_STEP);
                }
        }

        const Station *st;
        FOR_ALL_STATIONS(st) {
                if (DistanceSquare(st->xy, t->xy) <= t->cache.squared_town_zone_radius[0]) {
                        if (st->time_since_load <= 20 || st->time_since_unload <= 20) {
                                if (Company::IsValidID(st->owner)) {
                                        int new_rating = t->ratings[st->owner] + RATING_STATION_UP_STEP;
                                        t->ratings[st->owner] = min(new_rating, INT16_MAX); // do not let it overflow
                                }
                        } else {
                                if (Company::IsValidID(st->owner)) {
                                        int new_rating = t->ratings[st->owner] + RATING_STATION_DOWN_STEP;
                                        t->ratings[st->owner] = max(new_rating, INT16_MIN);
                                }
                        }
                }
        }

        /* clamp all ratings to valid values */
        for (uint i = 0; i < MAX_COMPANIES; i++) {
                t->ratings[i] = Clamp(t->ratings[i], RATING_MINIMUM, RATING_MAXIMUM);
        }

        SetWindowDirty(WC_TOWN_AUTHORITY, t->index);
}

static void UpdateTownGrowRate(Town *t)
{
        ClrBit(t->flags, TOWN_IS_GROWING);
        SetWindowDirty(WC_TOWN_VIEW, t->index);

        if (_settings_game.economy.town_growth_rate == 0 && t->fund_buildings_months == 0) return;

        if (t->fund_buildings_months == 0) {
                /* Check if all goals are reached for this town to grow (given we are not funding it) */
                for (int i = TE_BEGIN; i < TE_END; i++) {
                        switch (t->goal[i]) {
                                case TOWN_GROWTH_WINTER:
                                        if (TileHeight(t->xy) >= GetSnowLine() && t->received[i].old_act == 0 && t->cache.population > 90) return;
                                        break;
                                case TOWN_GROWTH_DESERT:
                                        if (GetTropicZone(t->xy) == TROPICZONE_DESERT && t->received[i].old_act == 0 && t->cache.population > 60) return;
                                        break;
                                default:
                                        if (t->goal[i] > t->received[i].old_act) return;
                                        break;
                        }
                }
        }

        if ((t->growth_rate & TOWN_GROW_RATE_CUSTOM) != 0) {
                if (t->growth_rate != TOWN_GROW_RATE_CUSTOM_NONE) SetBit(t->flags, TOWN_IS_GROWING);
                SetWindowDirty(WC_TOWN_VIEW, t->index);
                return;
        }

        /**
         * Towns are processed every TOWN_GROWTH_TICKS ticks, and this is the
         * number of times towns are processed before a new building is built.
         */
        static const uint16 _grow_count_values[2][6] = {
                { 120, 120, 120, 100,  80,  60 }, // Fund new buildings has been activated
                { 320, 420, 300, 220, 160, 100 }  // Normal values
        };

        int n = 0;

        const Station *st;
        FOR_ALL_STATIONS(st) {
                if (DistanceSquare(st->xy, t->xy) <= t->cache.squared_town_zone_radius[0]) {
                        if (st->time_since_load <= 20 || st->time_since_unload <= 20) {
                                n++;
                        }
                }
        }

        uint16 m;

        if (t->fund_buildings_months != 0) {
                m = _grow_count_values[0][min(n, 5)];
        } else {
                m = _grow_count_values[1][min(n, 5)];
                if (n == 0 && !Chance16(1, 12)) return;
        }

        /* Use the normal growth rate values if new buildings have been funded in
         * this town and the growth rate is set to none. */
        uint growth_multiplier = _settings_game.economy.town_growth_rate != 0 ? _settings_game.economy.town_growth_rate - 1 : 1;

        m >>= growth_multiplier;
        if (t->larger_town) m /= 2;

        t->growth_rate = m / (t->cache.num_houses / 50 + 1);
        t->grow_counter = min(t->growth_rate, t->grow_counter);

        SetBit(t->flags, TOWN_IS_GROWING);
        SetWindowDirty(WC_TOWN_VIEW, t->index);
}

static void UpdateTownAmounts(Town *t)
{
        for (CargoID i = 0; i < NUM_CARGO; i++) t->supplied[i].NewMonth();
        for (int i = TE_BEGIN; i < TE_END; i++) t->received[i].NewMonth();
        if (t->fund_buildings_months != 0) t->fund_buildings_months--;

        SetWindowDirty(WC_TOWN_VIEW, t->index);
}

static void UpdateTownUnwanted(Town *t)
{
        const Company *c;

        FOR_ALL_COMPANIES(c) {
                if (t->unwanted[c->index] > 0) t->unwanted[c->index]--;
        }
}

/**
 * Checks whether the local authority allows construction of a new station (rail, road, airport, dock) on the given tile
 * @param tile The tile where the station shall be constructed.
 * @param flags Command flags. DC_NO_TEST_TOWN_RATING is tested.
 * @return Succeeded or failed command.
 */
CommandCost CheckIfAuthorityAllowsNewStation(TileIndex tile, DoCommandFlag flags)
{
        if (!Company::IsValidID(_current_company) || (flags & DC_NO_TEST_TOWN_RATING)) return CommandCost();

        Town *t = LocalAuthorityTownFromTile(tile);
        if (t == NULL) return CommandCost();

        if (t->ratings[_current_company] > RATING_VERYPOOR) return CommandCost();

        SetDParam(0, t->index);
        return_cmd_error(STR_ERROR_LOCAL_AUTHORITY_REFUSES_TO_ALLOW_THIS);
}

/**
 * Return the town closest to the given tile.
 * @param tile Starting point of the search.
 * @return Closest town to \a tile, or \c NULL if there are no towns.
 *
 * @note This function only uses distance, the #ClosestTownFromTile function also takes town ownership into account.
 */
Town *CalcClosestTownFromTile(TileIndex tile)
{
        Town *t;
        uint best = UINT_MAX;
        Town *best_town = NULL;

        FOR_ALL_TOWNS(t) {
                uint dist = DistanceManhattan(tile, t->xy);
                if (dist < best) {
                        best = dist;
                        best_town = t;
                }
        }

        return best_town;
}

/**
 * Return the town closest (in distance or ownership) to a given tile, within a given threshold.
 * @param tile      Starting point of the search.
 * @param threshold Biggest allowed distance to the town.
 * @return Closest town to \a tile within \a threshold, or \c NULL if there is no such town.
 *
 * @note If you only care about distance, you can use the #CalcClosestTownFromTile function.
 */
Town *ClosestTownFromTile(TileIndex tile, uint threshold)
{
        if (IsHouseTile(tile)) {
                return Town::GetByTile(tile);
        } else if (IsRoadTile(tile) || IsLevelCrossingTile(tile)) {
                if (HasTownOwnedRoad(tile)) return Town::GetByTile(tile);

                TownID tid = GetTownIndex(tile);

                if (tid == (TownID)INVALID_TOWN) {
                        /* in the case we are generating "many random towns", this value may be INVALID_TOWN */
                        if (_generating_world) return threshold == UINT_MAX ? CalcClosestTownFromTile(tile) : Town::find_closest<DistanceManhattan> (tile, threshold - 1);
                        assert(Town::GetNumItems() == 0);
                        return NULL;
                }

                assert(Town::IsValidID(tid));
                Town *town = Town::Get(tid);

                if (DistanceManhattan(tile, town->xy) >= threshold) town = NULL;

                return town;
        }

        return threshold == UINT_MAX ? CalcClosestTownFromTile(tile) : Town::find_closest<DistanceManhattan> (tile, threshold - 1);
}

static bool _town_rating_test = false; ///< If \c true, town rating is in test-mode.
static SmallMap<const Town *, int, 4> _town_test_ratings; ///< Map of towns to modified ratings, while in town rating test-mode.

/**
 * Switch the town rating to test-mode, to allow commands to be tested without affecting current ratings.
 * The function is safe to use in nested calls.
 * @param mode Test mode switch (\c true means go to test-mode, \c false means leave test-mode).
 */
void SetTownRatingTestMode(bool mode)
{
        static int ref_count = 0; // Number of times test-mode is switched on.
        if (mode) {
                if (ref_count == 0) {
                        _town_test_ratings.Clear();
                }
                ref_count++;
        } else {
                assert(ref_count > 0);
                ref_count--;
        }
        _town_rating_test = !(ref_count == 0);
}

/**
 * Get the rating of a town for the #_current_company.
 * @param t Town to get the rating from.
 * @return Rating of the current company in the given town.
 */
static int GetRating(const Town *t)
{
        if (_town_rating_test) {
                SmallMap<const Town *, int>::iterator it = _town_test_ratings.Find(t);
                if (it != _town_test_ratings.End()) {
                        return it->second;
                }
        }
        return t->ratings[_current_company];
}

/**
 * Changes town rating of the current company
 * @param t Town to affect
 * @param add Value to add
 * @param max Minimum (add < 0) resp. maximum (add > 0) rating that should be achievable with this change.
 * @param flags Command flags, especially DC_NO_MODIFY_TOWN_RATING is tested
 */
void ChangeTownRating(Town *t, int add, int max, DoCommandFlag flags)
{
        /* if magic_bulldozer cheat is active, town doesn't penalize for removing stuff */
        if (t == NULL || (flags & DC_NO_MODIFY_TOWN_RATING) ||
                        !Company::IsValidID(_current_company) ||
                        (_cheats.magic_bulldozer.value && add < 0)) {
                return;
        }

        int rating = GetRating(t);
        if (add < 0) {
                if (rating > max) {
                        rating += add;
                        if (rating < max) rating = max;
                }
        } else {
                if (rating < max) {
                        rating += add;
                        if (rating > max) rating = max;
                }
        }
        if (_town_rating_test) {
                _town_test_ratings[t] = rating;
        } else {
                SetBit(t->have_ratings, _current_company);
                t->ratings[_current_company] = rating;
                SetWindowDirty(WC_TOWN_AUTHORITY, t->index);
        }
}

/**
 * Does the town authority allow the (destructive) action of the current company?
 * @param flags Checking flags of the command.
 * @param t     Town that must allow the company action.
 * @param type  Type of action that is wanted.
 * @return A succeeded command if the action is allowed, a failed command if it is not allowed.
 */
CommandCost CheckforTownRating(DoCommandFlag flags, Town *t, TownRatingCheckType type)
{
        /* if magic_bulldozer cheat is active, town doesn't restrict your destructive actions */
        if (t == NULL || !Company::IsValidID(_current_company) ||
                        _cheats.magic_bulldozer.value || (flags & DC_NO_TEST_TOWN_RATING)) {
                return CommandCost();
        }

        /* minimum rating needed to be allowed to remove stuff */
        static const int needed_rating[][TOWN_RATING_CHECK_TYPE_COUNT] = {
                /*                  ROAD_REMOVE,                    TUNNELBRIDGE_REMOVE */
                { RATING_ROAD_NEEDED_PERMISSIVE, RATING_TUNNEL_BRIDGE_NEEDED_PERMISSIVE}, // Permissive
                {    RATING_ROAD_NEEDED_NEUTRAL,    RATING_TUNNEL_BRIDGE_NEEDED_NEUTRAL}, // Neutral
                {    RATING_ROAD_NEEDED_HOSTILE,    RATING_TUNNEL_BRIDGE_NEEDED_HOSTILE}, // Hostile
        };

        /* check if you're allowed to remove the road/bridge/tunnel
         * owned by a town no removal if rating is lower than ... depends now on
         * difficulty setting. Minimum town rating selected by difficulty level
         */
        int needed = needed_rating[_settings_game.difficulty.town_council_tolerance][type];

        if (GetRating(t) < needed) {
                SetDParam(0, t->index);
                return_cmd_error(STR_ERROR_LOCAL_AUTHORITY_REFUSES_TO_ALLOW_THIS);
        }

        return CommandCost();
}

void TownsMonthlyLoop()
{
        Town *t;

        FOR_ALL_TOWNS(t) {
                if (t->road_build_months != 0) t->road_build_months--;

                if (t->exclusive_counter != 0) {
                        if (--t->exclusive_counter == 0) t->exclusivity = INVALID_COMPANY;
                }

                UpdateTownAmounts(t);
                UpdateTownRating(t);
                UpdateTownGrowRate(t);
                UpdateTownUnwanted(t);
                UpdateTownCargoes(t);
        }

        UpdateTownCargoBitmap();
}

void TownsYearlyLoop()
{
        /* Increment house ages */
        for (TileIndex t = 0; t < MapSize(); t++) {
                if (!IsHouseTile(t)) continue;
                IncrementHouseAge(t);
        }
}

static CommandCost TerraformTile_Town(TileIndex tile, DoCommandFlag flags, int z_new, Slope tileh_new)
{
        if (AutoslopeEnabled()) {
                HouseID house = GetHouseType(tile);
                GetHouseNorthPart(house); // modifies house to the ID of the north tile
                const HouseSpec *hs = HouseSpec::Get(house);

                /* Here we differ from TTDP by checking TILE_NOT_SLOPED */
                if (((hs->building_flags & TILE_NOT_SLOPED) == 0) && !IsSteepSlope(tileh_new) &&
                                (GetTileMaxZ(tile) == z_new + GetSlopeMaxZ(tileh_new))) {
                        bool allow_terraform = true;

                        /* Call the autosloping callback per tile, not for the whole building at once. */
                        house = GetHouseType(tile);
                        hs = HouseSpec::Get(house);
                        if (HasBit(hs->callback_mask, CBM_HOUSE_AUTOSLOPE)) {
                                /* If the callback fails, allow autoslope. */
                                uint16 res = GetHouseCallback(CBID_HOUSE_AUTOSLOPE, 0, 0, house, Town::GetByTile(tile), tile);
                                if (res != CALLBACK_FAILED && ConvertBooleanCallback(hs->grf_prop.grffile, CBID_HOUSE_AUTOSLOPE, res)) allow_terraform = false;
                        }

                        if (allow_terraform) return CommandCost(EXPENSES_CONSTRUCTION, _price[PR_BUILD_FOUNDATION]);
                }
        }

        return DoCommand(tile, 0, 0, flags, CMD_LANDSCAPE_CLEAR);
}

/** Tile callback functions for a town */
extern const TileTypeProcs _tile_type_town_procs = {
        DrawTile_Town,           // draw_tile_proc
        GetSlopePixelZ_Town,     // get_slope_z_proc
        ClearTile_Town,          // clear_tile_proc
        AddAcceptedCargo_Town,   // add_accepted_cargo_proc
        GetTileDesc_Town,        // get_tile_desc_proc
        NULL,                    // get_tile_railway_status_proc
        NULL,                    // get_tile_road_status_proc
        NULL,                    // get_tile_waterway_status_proc
        NULL,                    // click_tile_proc
        AnimateTile_Town,        // animate_tile_proc
        TileLoop_Town,           // tile_loop_proc
        ChangeTileOwner_Town,    // change_tile_owner_proc
        AddProducedCargo_Town,   // add_produced_cargo_proc
        GetFoundation_Town,      // get_foundation_proc
        TerraformTile_Town,      // terraform_tile_proc
};


HouseSpec _house_specs[NUM_HOUSES];

void ResetHouses()
{
        memset(&_house_specs, 0, sizeof(_house_specs));
        memcpy(&_house_specs, &_original_house_specs, sizeof(_original_house_specs));

        /* Reset any overrides that have been set. */
        _house_mngr.ResetOverride();
}