Add history graph API

[git/spearce.git] / graph.c

#include "cache.h"
#include "commit.h"
#include "graph.h"
#include "diff.h"
#include "revision.h"

/*
 * TODO:
 * - Add colors to the graph.
 *   Pick a color for each column, and print all characters
 *   in that column with the specified color.
 *
 * - Limit the number of columns, similar to the way gitk does.
 *   If we reach more than a specified number of columns, omit
 *   sections of some columns.
 *
 * - The output during the GRAPH_PRE_COMMIT and GRAPH_COLLAPSING states
 *   could be made more compact by printing horizontal lines, instead of
 *   long diagonal lines.  For example, during collapsing, something like
 *   this:          instead of this:
 *   | | | | |      | | | | |
 *   | |_|_|/       | | | |/
 *   |/| | |        | | |/|
 *   | | | |        | |/| |
 *                  |/| | |
 *                  | | | |
 *
 *   If there are several parallel diagonal lines, they will need to be
 *   replaced with horizontal lines on subsequent rows.
 */

struct column {
        /*
         * The parent commit of this column.
         */
        struct commit *commit;
        /*
         * XXX: Once we add support for colors, struct column could also
         * contain the color of its branch line.
         */
};

enum graph_state {
        GRAPH_PADDING,
        GRAPH_SKIP,
        GRAPH_PRE_COMMIT,
        GRAPH_COMMIT,
        GRAPH_POST_MERGE,
        GRAPH_COLLAPSING
};

struct git_graph {
        /*
         * The commit currently being processed
         */
        struct commit *commit;
        /*
         * The number of parents this commit has.
         * (Stored so we don't have to walk over them each time we need
         * this number)
         */
        int num_parents;
        /*
         * The next expansion row to print
         * when state is GRAPH_PRE_COMMIT
         */
        int expansion_row;
        /*
         * The current output state.
         * This tells us what kind of line graph_next_line() should output.
         */
        enum graph_state state;
        /*
         * The maximum number of columns that can be stored in the columns
         * and new_columns arrays.  This is also half the number of entries
         * that can be stored in the mapping and new_mapping arrays.
         */
        int column_capacity;
        /*
         * The number of columns (also called "branch lines" in some places)
         */
        int num_columns;
        /*
         * The number of columns in the new_columns array
         */
        int num_new_columns;
        /*
         * The number of entries in the mapping array
         */
        int mapping_size;
        /*
         * The column state before we output the current commit.
         */
        struct column *columns;
        /*
         * The new column state after we output the current commit.
         * Only valid when state is GRAPH_COLLAPSING.
         */
        struct column *new_columns;
        /*
         * An array that tracks the current state of each
         * character in the output line during state GRAPH_COLLAPSING.
         * Each entry is -1 if this character is empty, or a non-negative
         * integer if the character contains a branch line.  The value of
         * the integer indicates the target position for this branch line.
         * (I.e., this array maps the current column positions to their
         * desired positions.)
         *
         * The maximum capacity of this array is always
         * sizeof(int) * 2 * column_capacity.
         */
        int *mapping;
        /*
         * A temporary array for computing the next mapping state
         * while we are outputting a mapping line.  This is stored as part
         * of the git_graph simply so we don't have to allocate a new
         * temporary array each time we have to output a collapsing line.
         */
        int *new_mapping;
};

struct git_graph *graph_init(void)
{
        struct git_graph *graph = xmalloc(sizeof(struct git_graph));
        graph->commit = NULL;
        graph->num_parents = 0;
        graph->expansion_row = 0;
        graph->state = GRAPH_PADDING;
        graph->num_columns = 0;
        graph->num_new_columns = 0;
        graph->mapping_size = 0;

        /*
         * Allocate a reasonably large default number of columns
         * We'll automatically grow columns later if we need more room.
         */
        graph->column_capacity = 30;
        graph->columns = xmalloc(sizeof(struct column) *
                                 graph->column_capacity);
        graph->new_columns = xmalloc(sizeof(struct column) *
                                     graph->column_capacity);
        graph->mapping = xmalloc(sizeof(int) * 2 * graph->column_capacity);
        graph->new_mapping = xmalloc(sizeof(int) * 2 * graph->column_capacity);

        return graph;
}

void graph_release(struct git_graph *graph)
{
        free(graph->columns);
        free(graph->new_columns);
        free(graph->mapping);
        free(graph);
}

static void graph_ensure_capacity(struct git_graph *graph, int num_columns)
{
        if (graph->column_capacity >= num_columns)
                return;

        do {
                graph->column_capacity *= 2;
        } while (graph->column_capacity < num_columns);

        graph->columns = xrealloc(graph->columns,
                                  sizeof(struct column) *
                                  graph->column_capacity);
        graph->new_columns = xrealloc(graph->new_columns,
                                      sizeof(struct column) *
                                      graph->column_capacity);
        graph->mapping = xrealloc(graph->mapping,
                                  sizeof(int) * 2 * graph->column_capacity);
        graph->new_mapping = xrealloc(graph->new_mapping,
                                      sizeof(int) * 2 * graph->column_capacity);
}

static void graph_insert_into_new_columns(struct git_graph *graph,
                                          struct commit *commit,
                                          int *mapping_index)
{
        int i;

        /*
         * Ignore uinteresting and pruned commits
         */
        if (commit->object.flags & (UNINTERESTING | TREESAME))
                return;

        /*
         * If the commit is already in the new_columns list, we don't need to
         * add it.  Just update the mapping correctly.
         */
        for (i = 0; i < graph->num_new_columns; i++) {
                if (graph->new_columns[i].commit == commit) {
                        graph->mapping[*mapping_index] = i;
                        *mapping_index += 2;
                        return;
                }
        }

        /*
         * This commit isn't already in new_columns.  Add it.
         */
        graph->new_columns[graph->num_new_columns].commit = commit;
        graph->mapping[*mapping_index] = graph->num_new_columns;
        *mapping_index += 2;
        graph->num_new_columns++;
}

static void graph_update_columns(struct git_graph *graph)
{
        struct commit_list *parent;
        struct column *tmp_columns;
        int max_new_columns;
        int mapping_idx;
        int i, seen_this;

        /*
         * Swap graph->columns with graph->new_columns
         * graph->columns contains the state for the previous commit,
         * and new_columns now contains the state for our commit.
         *
         * We'll re-use the old columns array as storage to compute the new
         * columns list for the commit after this one.
         */
        tmp_columns = graph->columns;
        graph->columns = graph->new_columns;
        graph->num_columns = graph->num_new_columns;

        graph->new_columns = tmp_columns;
        graph->num_new_columns = 0;

        /*
         * Now update new_columns and mapping with the information for the
         * commit after this one.
         *
         * First, make sure we have enough room.  At most, there will
         * be graph->num_columns + graph->num_parents columns for the next
         * commit.
         */
        max_new_columns = graph->num_columns + graph->num_parents;
        graph_ensure_capacity(graph, max_new_columns);

        /*
         * Clear out graph->mapping
         */
        graph->mapping_size = 2 * max_new_columns;
        for (i = 0; i < graph->mapping_size; i++)
                graph->mapping[i] = -1;

        /*
         * Populate graph->new_columns and graph->mapping
         *
         * Some of the parents of this commit may already be in
         * graph->columns.  If so, graph->new_columns should only contain a
         * single entry for each such commit.  graph->mapping should
         * contain information about where each current branch line is
         * supposed to end up after the collapsing is performed.
         */
        seen_this = 0;
        mapping_idx = 0;
        for (i = 0; i <= graph->num_columns; i++) {
                struct commit *col_commit;
                if (i == graph->num_columns) {
                        if (seen_this)
                                break;
                        col_commit = graph->commit;
                } else {
                        col_commit = graph->columns[i].commit;
                }

                if (col_commit == graph->commit) {
                        seen_this = 1;
                        for (parent = graph->commit->parents;
                             parent;
                             parent = parent->next) {
                                graph_insert_into_new_columns(graph,
                                                              parent->item,
                                                              &mapping_idx);
                        }
                } else {
                        graph_insert_into_new_columns(graph, col_commit,
                                                      &mapping_idx);
                }
        }

        /*
         * Shrink mapping_size to be the minimum necessary
         */
        while (graph->mapping_size > 1 &&
               graph->mapping[graph->mapping_size - 1] < 0)
                graph->mapping_size--;
}

void graph_update(struct git_graph *graph, struct commit *commit)
{
        struct commit_list *parent;

        /*
         * Set the new commit
         */
        graph->commit = commit;

        /*
         * Count how many parents this commit has
         */
        graph->num_parents = 0;
        for (parent = commit->parents; parent; parent = parent->next)
                graph->num_parents++;

        /*
         * Call graph_update_columns() to update
         * columns, new_columns, and mapping.
         */
        graph_update_columns(graph);

        graph->expansion_row = 0;

        /*
         * Update graph->state.
         *
         * If the previous commit didn't get to the GRAPH_PADDING state,
         * it never finished its output.  Goto GRAPH_SKIP, to print out
         * a line to indicate that portion of the graph is missing.
         *
         * Otherwise, if there are 3 or more parents, we need to print
         * extra rows before the commit, to expand the branch lines around
         * it and make room for it.
         *
         * If there are less than 3 parents, we can immediately print the
         * commit line.
         */
        if (graph->state != GRAPH_PADDING)
                graph->state = GRAPH_SKIP;
        else if (graph->num_parents >= 3)
                graph->state = GRAPH_PRE_COMMIT;
        else
                graph->state = GRAPH_COMMIT;
}

static int graph_is_mapping_correct(struct git_graph *graph)
{
        int i;

        /*
         * The mapping is up to date if each entry is at its target,
         * or is 1 greater than its target.
         * (If it is 1 greater than the target, '/' will be printed, so it
         * will look correct on the next row.)
         */
        for (i = 0; i < graph->mapping_size; i++) {
                int target = graph->mapping[i];
                if (target < 0)
                        continue;
                if (target == (i / 2))
                        continue;
                return 0;
        }

        return 1;
}

static void graph_pad_horizontally(struct git_graph *graph, struct strbuf *sb)
{
        /*
         * Add additional spaces to the end of the strbuf, so that all
         * lines for a particular commit have the same width.
         *
         * This way, fields printed to the right of the graph will remain
         * aligned for the entire commit.
         *
         * This computation results in 3 extra space to the right in most
         * cases, but only 1 extra space if the commit doesn't have any
         * children that have already been displayed in the graph (i.e.,
         * if the current commit isn't in graph->columns).
         */
        size_t extra;
        size_t final_width = graph->num_columns + graph->num_parents;
        if (graph->num_parents < 1)
                final_width++;
        final_width *= 2;

        if (sb->len >= final_width)
                return;

        extra = final_width - sb->len;
        strbuf_addf(sb, "%*s", (int) extra, "");
}

static void graph_output_padding_line(struct git_graph *graph,
                                      struct strbuf *sb)
{
        int i;

        /*
         * We could conceivable be called with a NULL commit
         * if our caller has a bug, and invokes graph_next_line()
         * immediately after graph_init(), without first calling
         * graph_update().  Return without outputting anything in this
         * case.
         */
        if (!graph->commit)
                return;

        /*
         * Output a padding row, that leaves all branch lines unchanged
         */
        for (i = 0; i < graph->num_new_columns; i++) {
                strbuf_addstr(sb, "| ");
        }

        graph_pad_horizontally(graph, sb);
}

static void graph_output_skip_line(struct git_graph *graph, struct strbuf *sb)
{
        /*
         * Output an ellipsis to indicate that a portion
         * of the graph is missing.
         */
        strbuf_addstr(sb, "...");
        graph_pad_horizontally(graph, sb);

        if (graph->num_parents >= 3)
                graph->state = GRAPH_PRE_COMMIT;
        else
                graph->state = GRAPH_COMMIT;
}

static void graph_output_pre_commit_line(struct git_graph *graph,
                                         struct strbuf *sb)
{
        int num_expansion_rows;
        int i, seen_this;

        /*
         * This function formats a row that increases the space around a commit
         * with multiple parents, to make room for it.  It should only be
         * called when there are 3 or more parents.
         *
         * We need 2 extra rows for every parent over 2.
         */
        assert(graph->num_parents >= 3);
        num_expansion_rows = (graph->num_parents - 2) * 2;

        /*
         * graph->expansion_row tracks the current expansion row we are on.
         * It should be in the range [0, num_expansion_rows - 1]
         */
        assert(0 <= graph->expansion_row &&
               graph->expansion_row < num_expansion_rows);

        /*
         * Output the row
         */
        seen_this = 0;
        for (i = 0; i < graph->num_columns; i++) {
                struct column *col = &graph->columns[i];
                if (col->commit == graph->commit) {
                        seen_this = 1;
                        strbuf_addf(sb, "| %*s", graph->expansion_row, "");
                } else if (seen_this) {
                        strbuf_addstr(sb, "\\ ");
                } else {
                        strbuf_addstr(sb, "| ");
                }
        }

        graph_pad_horizontally(graph, sb);

        /*
         * Increment graph->expansion_row,
         * and move to state GRAPH_COMMIT if necessary
         */
        graph->expansion_row++;
        if (graph->expansion_row >= num_expansion_rows)
                graph->state = GRAPH_COMMIT;
}

void graph_output_commit_line(struct git_graph *graph, struct strbuf *sb)
{
        int seen_this = 0;
        int i, j;

        /*
         * Output the row containing this commit
         * Iterate up to and including graph->num_columns,
         * since the current commit may not be in any of the existing
         * columns.  (This happens when the current commit doesn't have any
         * children that we have already processed.)
         */
        seen_this = 0;
        for (i = 0; i <= graph->num_columns; i++) {
                struct commit *col_commit;
                if (i == graph->num_columns) {
                        if (seen_this)
                                break;
                        col_commit = graph->commit;
                } else {
                        col_commit = graph->columns[i].commit;
                }

                if (col_commit == graph->commit) {
                        seen_this = 1;
                        if (graph->num_parents > 1)
                                strbuf_addch(sb, 'M');
                        else
                                strbuf_addch(sb, '*');

                        if (graph->num_parents < 2)
                                strbuf_addch(sb, ' ');
                        else if (graph->num_parents == 2)
                                strbuf_addstr(sb, "  ");
                        else {
                                int num_dashes =
                                        ((graph->num_parents - 2) * 2) - 1;
                                for (j = 0; j < num_dashes; j++)
                                        strbuf_addch(sb, '-');
                                strbuf_addstr(sb, ". ");
                        }
                } else if (seen_this && (graph->num_parents > 1)) {
                        strbuf_addstr(sb, "\\ ");
                } else {
                        strbuf_addstr(sb, "| ");
                }
        }

        graph_pad_horizontally(graph, sb);

        /*
         * Update graph->state
         */
        if (graph->num_parents > 1)
                graph->state = GRAPH_POST_MERGE;
        else if (graph_is_mapping_correct(graph))
                graph->state = GRAPH_PADDING;
        else
                graph->state = GRAPH_COLLAPSING;
}

void graph_output_post_merge_line(struct git_graph *graph, struct strbuf *sb)
{
        int seen_this = 0;
        int i, j;

        /*
         * Output the post-merge row
         */
        for (i = 0; i <= graph->num_columns; i++) {
                struct commit *col_commit;
                if (i == graph->num_columns) {
                        if (seen_this)
                                break;
                        col_commit = graph->commit;
                } else {
                        col_commit = graph->columns[i].commit;
                }

                if (col_commit == graph->commit) {
                        seen_this = 1;
                        strbuf_addch(sb, '|');
                        for (j = 0; j < graph->num_parents - 1; j++)
                                strbuf_addstr(sb, "\\ ");
                        if (graph->num_parents == 2)
                                strbuf_addch(sb, ' ');
                } else if (seen_this && (graph->num_parents > 2)) {
                        strbuf_addstr(sb, "\\ ");
                } else {
                        strbuf_addstr(sb, "| ");
                }
        }

        graph_pad_horizontally(graph, sb);

        /*
         * Update graph->state
         */
        if (graph_is_mapping_correct(graph))
                graph->state = GRAPH_PADDING;
        else
                graph->state = GRAPH_COLLAPSING;
}

void graph_output_collapsing_line(struct git_graph *graph, struct strbuf *sb)
{
        int i;
        int *tmp_mapping;

        /*
         * Clear out the new_mapping array
         */
        for (i = 0; i < graph->mapping_size; i++)
                graph->new_mapping[i] = -1;

        for (i = 0; i < graph->mapping_size; i++) {
                int target = graph->mapping[i];
                if (target < 0)
                        continue;

                /*
                 * Since update_columns() always inserts the leftmost
                 * column first, each branch's target location should
                 * always be either its current location or to the left of
                 * its current location.
                 *
                 * We never have to move branches to the right.  This makes
                 * the graph much more legible, since whenever branches
                 * cross, only one is moving directions.
                 */
                assert(target * 2 <= i);

                if (target * 2 == i) {
                        /*
                         * This column is already in the
                         * correct place
                         */
                        assert(graph->new_mapping[i] == -1);
                        graph->new_mapping[i] = target;
                } else if (graph->new_mapping[i - 1] < 0) {
                        /*
                         * Nothing is to the left.
                         * Move to the left by one
                         */
                        graph->new_mapping[i - 1] = target;
                } else if (graph->new_mapping[i - 1] == target) {
                        /*
                         * There is a branch line to our left
                         * already, and it is our target.  We
                         * combine with this line, since we share
                         * the same parent commit.
                         *
                         * We don't have to add anything to the
                         * output or new_mapping, since the
                         * existing branch line has already taken
                         * care of it.
                         */
                } else {
                        /*
                         * There is a branch line to our left,
                         * but it isn't our target.  We need to
                         * cross over it.
                         *
                         * The space just to the left of this
                         * branch should always be empty.
                         */
                        assert(graph->new_mapping[i - 1] > target);
                        assert(graph->new_mapping[i - 2] < 0);
                        graph->new_mapping[i - 2] = target;
                }
        }

        /*
         * The new mapping may be 1 smaller than the old mapping
         */
        if (graph->new_mapping[graph->mapping_size - 1] < 0)
                graph->mapping_size--;

        /*
         * Output out a line based on the new mapping info
         */
        for (i = 0; i < graph->mapping_size; i++) {
                int target = graph->new_mapping[i];
                if (target < 0)
                        strbuf_addch(sb, ' ');
                else if (target * 2 == i)
                        strbuf_addch(sb, '|');
                else
                        strbuf_addch(sb, '/');
        }

        graph_pad_horizontally(graph, sb);

        /*
         * Swap mapping and new_mapping
         */
        tmp_mapping = graph->mapping;
        graph->mapping = graph->new_mapping;
        graph->new_mapping = tmp_mapping;

        /*
         * If graph->mapping indicates that all of the branch lines
         * are already in the correct positions, we are done.
         * Otherwise, we need to collapse some branch lines together.
         */
        if (graph_is_mapping_correct(graph))
                graph->state = GRAPH_PADDING;
}

int graph_next_line(struct git_graph *graph, struct strbuf *sb)
{
        switch (graph->state) {
        case GRAPH_PADDING:
                graph_output_padding_line(graph, sb);
                return 0;
        case GRAPH_SKIP:
                graph_output_skip_line(graph, sb);
                return 0;
        case GRAPH_PRE_COMMIT:
                graph_output_pre_commit_line(graph, sb);
                return 0;
        case GRAPH_COMMIT:
                graph_output_commit_line(graph, sb);
                return 1;
        case GRAPH_POST_MERGE:
                graph_output_post_merge_line(graph, sb);
                return 0;
        case GRAPH_COLLAPSING:
                graph_output_collapsing_line(graph, sb);
                return 0;
        }

        assert(0);
        return 0;
}

void graph_padding_line(struct git_graph *graph, struct strbuf *sb)
{
        int i, j;

        if (graph->state != GRAPH_COMMIT) {
                graph_next_line(graph, sb);
                return;
        }

        /*
         * Output the row containing this commit
         * Iterate up to and including graph->num_columns,
         * since the current commit may not be in any of the existing
         * columns.  (This happens when the current commit doesn't have any
         * children that we have already processed.)
         */
        for (i = 0; i < graph->num_columns; i++) {
                struct commit *col_commit = graph->columns[i].commit;
                if (col_commit == graph->commit) {
                        strbuf_addch(sb, '|');

                        if (graph->num_parents < 3)
                                strbuf_addch(sb, ' ');
                        else {
                                int num_spaces = ((graph->num_parents - 2) * 2);
                                for (j = 0; j < num_spaces; j++)
                                        strbuf_addch(sb, ' ');
                        }
                } else {
                        strbuf_addstr(sb, "| ");
                }
        }

        graph_pad_horizontally(graph, sb);
}

int graph_is_commit_finished(struct git_graph const *graph)
{
        return (graph->state == GRAPH_PADDING);
}

void graph_show_commit(struct git_graph *graph)
{
        struct strbuf msgbuf;
        int shown_commit_line = 0;

        if (!graph)
                return;

        strbuf_init(&msgbuf, 0);

        while (!shown_commit_line) {
                shown_commit_line = graph_next_line(graph, &msgbuf);
                fwrite(msgbuf.buf, sizeof(char), msgbuf.len, stdout);
                if (!shown_commit_line)
                        putchar('\n');
                strbuf_setlen(&msgbuf, 0);
        }

        strbuf_release(&msgbuf);
}

void graph_show_oneline(struct git_graph *graph)
{
        struct strbuf msgbuf;

        if (!graph)
                return;

        strbuf_init(&msgbuf, 0);
        graph_next_line(graph, &msgbuf);
        fwrite(msgbuf.buf, sizeof(char), msgbuf.len, stdout);
        strbuf_release(&msgbuf);
}

void graph_show_padding(struct git_graph *graph)
{
        struct strbuf msgbuf;

        if (!graph)
                return;

        strbuf_init(&msgbuf, 0);
        graph_padding_line(graph, &msgbuf);
        fwrite(msgbuf.buf, sizeof(char), msgbuf.len, stdout);
        strbuf_release(&msgbuf);
}

int graph_show_remainder(struct git_graph *graph)
{
        struct strbuf msgbuf;
        int shown = 0;

        if (!graph)
                return 0;

        if (graph_is_commit_finished(graph))
                return 0;

        strbuf_init(&msgbuf, 0);
        for (;;) {
                graph_next_line(graph, &msgbuf);
                fwrite(msgbuf.buf, sizeof(char), msgbuf.len, stdout);
                strbuf_setlen(&msgbuf, 0);
                shown = 1;

                if (!graph_is_commit_finished(graph))
                        putchar('\n');
                else
                        break;
        }
        strbuf_release(&msgbuf);

        return shown;
}


void graph_show_strbuf(struct git_graph *graph, struct strbuf const *sb)
{
        char *p;

        if (!graph) {
                fwrite(sb->buf, sizeof(char), sb->len, stdout);
                return;
        }

        /*
         * Print the strbuf line by line,
         * and display the graph info before each line but the first.
         */
        p = sb->buf;
        while (p) {
                size_t len;
                char *next_p = strchr(p, '\n');
                if (next_p) {
                        next_p++;
                        len = next_p - p;
                } else {
                        len = (sb->buf + sb->len) - p;
                }
                fwrite(p, sizeof(char), len, stdout);
                if (next_p && *next_p != '\0')
                        graph_show_oneline(graph);
                p = next_p;
        }
}

void graph_show_commit_msg(struct git_graph *graph,
                           struct strbuf const *sb)
{
        int newline_terminated;

        if (!graph) {
                /*
                 * If there's no graph, just print the message buffer.
                 *
                 * The message buffer for CMIT_FMT_ONELINE and
                 * CMIT_FMT_USERFORMAT are already missing a terminating
                 * newline.  All of the other formats should have it.
                 */
                fwrite(sb->buf, sizeof(char), sb->len, stdout);
                return;
        }

        newline_terminated = (sb->len && sb->buf[sb->len - 1] == '\n');

        /*
         * Show the commit message
         */
        graph_show_strbuf(graph, sb);

        /*
         * If there is more output needed for this commit, show it now
         */
        if (!graph_is_commit_finished(graph)) {
                /*
                 * If sb doesn't have a terminating newline, print one now,
                 * so we can start the remainder of the graph output on a
                 * new line.
                 */
                if (!newline_terminated)
                        putchar('\n');

                graph_show_remainder(graph);

                /*
                 * If sb ends with a newline, our output should too.
                 */
                if (newline_terminated)
                        putchar('\n');
        }
}