Improve HTML rendition of some annotations

[geany-mirror.git] / scintilla / src / CellBuffer.cxx

// Scintilla source code edit control
/** @file CellBuffer.cxx
 ** Manages a buffer of cells.
 **/
// Copyright 1998-2001 by Neil Hodgson <neilh@scintilla.org>
// The License.txt file describes the conditions under which this software may be distributed.

#include <stdlib.h>
#include <string.h>
#include <stdio.h>
#include <stdarg.h>

#include <stdexcept>
#include <algorithm>

#include "Platform.h"

#include "Scintilla.h"
#include "Position.h"
#include "SplitVector.h"
#include "Partitioning.h"
#include "CellBuffer.h"
#include "UniConversion.h"

#ifdef SCI_NAMESPACE
using namespace Scintilla;
#endif

LineVector::LineVector() : starts(256), perLine(0) {
        Init();
}

LineVector::~LineVector() {
        starts.DeleteAll();
}

void LineVector::Init() {
        starts.DeleteAll();
        if (perLine) {
                perLine->Init();
        }
}

void LineVector::SetPerLine(PerLine *pl) {
        perLine = pl;
}

void LineVector::InsertText(int line, int delta) {
        starts.InsertText(line, delta);
}

void LineVector::InsertLine(int line, int position, bool lineStart) {
        starts.InsertPartition(line, position);
        if (perLine) {
                if ((line > 0) && lineStart)
                        line--;
                perLine->InsertLine(line);
        }
}

void LineVector::SetLineStart(int line, int position) {
        starts.SetPartitionStartPosition(line, position);
}

void LineVector::RemoveLine(int line) {
        starts.RemovePartition(line);
        if (perLine) {
                perLine->RemoveLine(line);
        }
}

int LineVector::LineFromPosition(int pos) const {
        return starts.PartitionFromPosition(pos);
}

Action::Action() {
        at = startAction;
        position = 0;
        data = 0;
        lenData = 0;
        mayCoalesce = false;
}

Action::~Action() {
        Destroy();
}

void Action::Create(actionType at_, int position_, const char *data_, int lenData_, bool mayCoalesce_) {
        delete []data;
        data = NULL;
        position = position_;
        at = at_;
        if (lenData_) {
                data = new char[lenData_];
                memcpy(data, data_, lenData_);
        }
        lenData = lenData_;
        mayCoalesce = mayCoalesce_;
}

void Action::Destroy() {
        delete []data;
        data = 0;
}

void Action::Grab(Action *source) {
        delete []data;

        position = source->position;
        at = source->at;
        data = source->data;
        lenData = source->lenData;
        mayCoalesce = source->mayCoalesce;

        // Ownership of source data transferred to this
        source->position = 0;
        source->at = startAction;
        source->data = 0;
        source->lenData = 0;
        source->mayCoalesce = true;
}

// The undo history stores a sequence of user operations that represent the user's view of the
// commands executed on the text.
// Each user operation contains a sequence of text insertion and text deletion actions.
// All the user operations are stored in a list of individual actions with 'start' actions used
// as delimiters between user operations.
// Initially there is one start action in the history.
// As each action is performed, it is recorded in the history. The action may either become
// part of the current user operation or may start a new user operation. If it is to be part of the
// current operation, then it overwrites the current last action. If it is to be part of a new
// operation, it is appended after the current last action.
// After writing the new action, a new start action is appended at the end of the history.
// The decision of whether to start a new user operation is based upon two factors. If a
// compound operation has been explicitly started by calling BeginUndoAction and no matching
// EndUndoAction (these calls nest) has been called, then the action is coalesced into the current
// operation. If there is no outstanding BeginUndoAction call then a new operation is started
// unless it looks as if the new action is caused by the user typing or deleting a stream of text.
// Sequences that look like typing or deletion are coalesced into a single user operation.

UndoHistory::UndoHistory() {

        lenActions = 100;
        actions = new Action[lenActions];
        maxAction = 0;
        currentAction = 0;
        undoSequenceDepth = 0;
        savePoint = 0;
        tentativePoint = -1;

        actions[currentAction].Create(startAction);
}

UndoHistory::~UndoHistory() {
        delete []actions;
        actions = 0;
}

void UndoHistory::EnsureUndoRoom() {
        // Have to test that there is room for 2 more actions in the array
        // as two actions may be created by the calling function
        if (currentAction >= (lenActions - 2)) {
                // Run out of undo nodes so extend the array
                int lenActionsNew = lenActions * 2;
                Action *actionsNew = new Action[lenActionsNew];
                for (int act = 0; act <= currentAction; act++)
                        actionsNew[act].Grab(&actions[act]);
                delete []actions;
                lenActions = lenActionsNew;
                actions = actionsNew;
        }
}

const char *UndoHistory::AppendAction(actionType at, int position, const char *data, int lengthData,
        bool &startSequence, bool mayCoalesce) {
        EnsureUndoRoom();
        //Platform::DebugPrintf("%% %d action %d %d %d\n", at, position, lengthData, currentAction);
        //Platform::DebugPrintf("^ %d action %d %d\n", actions[currentAction - 1].at,
        //      actions[currentAction - 1].position, actions[currentAction - 1].lenData);
        if (currentAction < savePoint) {
                savePoint = -1;
        }
        int oldCurrentAction = currentAction;
        if (currentAction >= 1) {
                if (0 == undoSequenceDepth) {
                        // Top level actions may not always be coalesced
                        int targetAct = -1;
                        const Action *actPrevious = &(actions[currentAction + targetAct]);
                        // Container actions may forward the coalesce state of Scintilla Actions.
                        while ((actPrevious->at == containerAction) && actPrevious->mayCoalesce) {
                                targetAct--;
                                actPrevious = &(actions[currentAction + targetAct]);
                        }
                        // See if current action can be coalesced into previous action
                        // Will work if both are inserts or deletes and position is same
#if defined(_MSC_VER) && defined(_PREFAST_)
                        // Visual Studio 2013 Code Analysis wrongly believes actions can be NULL at its next reference
                        __analysis_assume(actions);
#endif
                        if ((currentAction == savePoint) || (currentAction == tentativePoint)) {
                                currentAction++;
                        } else if (!actions[currentAction].mayCoalesce) {
                                // Not allowed to coalesce if this set
                                currentAction++;
                        } else if (!mayCoalesce || !actPrevious->mayCoalesce) {
                                currentAction++;
                        } else if (at == containerAction || actions[currentAction].at == containerAction) {
                                ;       // A coalescible containerAction
                        } else if ((at != actPrevious->at) && (actPrevious->at != startAction)) {
                                currentAction++;
                        } else if ((at == insertAction) &&
                                   (position != (actPrevious->position + actPrevious->lenData))) {
                                // Insertions must be immediately after to coalesce
                                currentAction++;
                        } else if (at == removeAction) {
                                if ((lengthData == 1) || (lengthData == 2)) {
                                        if ((position + lengthData) == actPrevious->position) {
                                                ; // Backspace -> OK
                                        } else if (position == actPrevious->position) {
                                                ; // Delete -> OK
                                        } else {
                                                // Removals must be at same position to coalesce
                                                currentAction++;
                                        }
                                } else {
                                        // Removals must be of one character to coalesce
                                        currentAction++;
                                }
                        } else {
                                // Action coalesced.
                        }

                } else {
                        // Actions not at top level are always coalesced unless this is after return to top level
                        if (!actions[currentAction].mayCoalesce)
                                currentAction++;
                }
        } else {
                currentAction++;
        }
        startSequence = oldCurrentAction != currentAction;
        int actionWithData = currentAction;
        actions[currentAction].Create(at, position, data, lengthData, mayCoalesce);
        currentAction++;
        actions[currentAction].Create(startAction);
        maxAction = currentAction;
        return actions[actionWithData].data;
}

void UndoHistory::BeginUndoAction() {
        EnsureUndoRoom();
        if (undoSequenceDepth == 0) {
                if (actions[currentAction].at != startAction) {
                        currentAction++;
                        actions[currentAction].Create(startAction);
                        maxAction = currentAction;
                }
                actions[currentAction].mayCoalesce = false;
        }
        undoSequenceDepth++;
}

void UndoHistory::EndUndoAction() {
        PLATFORM_ASSERT(undoSequenceDepth > 0);
        EnsureUndoRoom();
        undoSequenceDepth--;
        if (0 == undoSequenceDepth) {
                if (actions[currentAction].at != startAction) {
                        currentAction++;
                        actions[currentAction].Create(startAction);
                        maxAction = currentAction;
                }
                actions[currentAction].mayCoalesce = false;
        }
}

void UndoHistory::DropUndoSequence() {
        undoSequenceDepth = 0;
}

void UndoHistory::DeleteUndoHistory() {
        for (int i = 1; i < maxAction; i++)
                actions[i].Destroy();
        maxAction = 0;
        currentAction = 0;
        actions[currentAction].Create(startAction);
        savePoint = 0;
        tentativePoint = -1;
}

void UndoHistory::SetSavePoint() {
        savePoint = currentAction;
}

bool UndoHistory::IsSavePoint() const {
        return savePoint == currentAction;
}

void UndoHistory::TentativeStart() {
        tentativePoint = currentAction;
}

void UndoHistory::TentativeCommit() {
        tentativePoint = -1;
        // Truncate undo history
        maxAction = currentAction;
}

int UndoHistory::TentativeSteps() {
        // Drop any trailing startAction
        if (actions[currentAction].at == startAction && currentAction > 0)
                currentAction--;
        if (tentativePoint >= 0)
                return currentAction - tentativePoint;
        else
                return -1;
}

bool UndoHistory::CanUndo() const {
        return (currentAction > 0) && (maxAction > 0);
}

int UndoHistory::StartUndo() {
        // Drop any trailing startAction
        if (actions[currentAction].at == startAction && currentAction > 0)
                currentAction--;

        // Count the steps in this action
        int act = currentAction;
        while (actions[act].at != startAction && act > 0) {
                act--;
        }
        return currentAction - act;
}

const Action &UndoHistory::GetUndoStep() const {
        return actions[currentAction];
}

void UndoHistory::CompletedUndoStep() {
        currentAction--;
}

bool UndoHistory::CanRedo() const {
        return maxAction > currentAction;
}

int UndoHistory::StartRedo() {
        // Drop any leading startAction
        if (actions[currentAction].at == startAction && currentAction < maxAction)
                currentAction++;

        // Count the steps in this action
        int act = currentAction;
        while (actions[act].at != startAction && act < maxAction) {
                act++;
        }
        return act - currentAction;
}

const Action &UndoHistory::GetRedoStep() const {
        return actions[currentAction];
}

void UndoHistory::CompletedRedoStep() {
        currentAction++;
}

CellBuffer::CellBuffer() {
        readOnly = false;
        utf8LineEnds = 0;
        collectingUndo = true;
}

CellBuffer::~CellBuffer() {
}

char CellBuffer::CharAt(int position) const {
        return substance.ValueAt(position);
}

void CellBuffer::GetCharRange(char *buffer, int position, int lengthRetrieve) const {
        if (lengthRetrieve <= 0)
                return;
        if (position < 0)
                return;
        if ((position + lengthRetrieve) > substance.Length()) {
                Platform::DebugPrintf("Bad GetCharRange %d for %d of %d\n", position,
                                      lengthRetrieve, substance.Length());
                return;
        }
        substance.GetRange(buffer, position, lengthRetrieve);
}

char CellBuffer::StyleAt(int position) const {
        return style.ValueAt(position);
}

void CellBuffer::GetStyleRange(unsigned char *buffer, int position, int lengthRetrieve) const {
        if (lengthRetrieve < 0)
                return;
        if (position < 0)
                return;
        if ((position + lengthRetrieve) > style.Length()) {
                Platform::DebugPrintf("Bad GetStyleRange %d for %d of %d\n", position,
                                      lengthRetrieve, style.Length());
                return;
        }
        style.GetRange(reinterpret_cast<char *>(buffer), position, lengthRetrieve);
}

const char *CellBuffer::BufferPointer() {
        return substance.BufferPointer();
}

const char *CellBuffer::RangePointer(int position, int rangeLength) {
        return substance.RangePointer(position, rangeLength);
}

int CellBuffer::GapPosition() const {
        return substance.GapPosition();
}

// The char* returned is to an allocation owned by the undo history
const char *CellBuffer::InsertString(int position, const char *s, int insertLength, bool &startSequence) {
        // InsertString and DeleteChars are the bottleneck though which all changes occur
        const char *data = s;
        if (!readOnly) {
                if (collectingUndo) {
                        // Save into the undo/redo stack, but only the characters - not the formatting
                        // This takes up about half load time
                        data = uh.AppendAction(insertAction, position, s, insertLength, startSequence);
                }

                BasicInsertString(position, s, insertLength);
        }
        return data;
}

bool CellBuffer::SetStyleAt(int position, char styleValue) {
        char curVal = style.ValueAt(position);
        if (curVal != styleValue) {
                style.SetValueAt(position, styleValue);
                return true;
        } else {
                return false;
        }
}

bool CellBuffer::SetStyleFor(int position, int lengthStyle, char styleValue) {
        bool changed = false;
        PLATFORM_ASSERT(lengthStyle == 0 ||
                (lengthStyle > 0 && lengthStyle + position <= style.Length()));
        while (lengthStyle--) {
                char curVal = style.ValueAt(position);
                if (curVal != styleValue) {
                        style.SetValueAt(position, styleValue);
                        changed = true;
                }
                position++;
        }
        return changed;
}

// The char* returned is to an allocation owned by the undo history
const char *CellBuffer::DeleteChars(int position, int deleteLength, bool &startSequence) {
        // InsertString and DeleteChars are the bottleneck though which all changes occur
        PLATFORM_ASSERT(deleteLength > 0);
        const char *data = 0;
        if (!readOnly) {
                if (collectingUndo) {
                        // Save into the undo/redo stack, but only the characters - not the formatting
                        // The gap would be moved to position anyway for the deletion so this doesn't cost extra
                        data = substance.RangePointer(position, deleteLength);
                        data = uh.AppendAction(removeAction, position, data, deleteLength, startSequence);
                }

                BasicDeleteChars(position, deleteLength);
        }
        return data;
}

int CellBuffer::Length() const {
        return substance.Length();
}

void CellBuffer::Allocate(int newSize) {
        substance.ReAllocate(newSize);
        style.ReAllocate(newSize);
}

void CellBuffer::SetLineEndTypes(int utf8LineEnds_) {
        if (utf8LineEnds != utf8LineEnds_) {
                utf8LineEnds = utf8LineEnds_;
                ResetLineEnds();
        }
}

bool CellBuffer::ContainsLineEnd(const char *s, int length) const {
        unsigned char chBeforePrev = 0;
        unsigned char chPrev = 0;
        for (int i = 0; i < length; i++) {
                const unsigned char ch = s[i];
                if ((ch == '\r') || (ch == '\n')) {
                        return true;
                } else if (utf8LineEnds) {
                        unsigned char back3[3] = { chBeforePrev, chPrev, ch };
                        if (UTF8IsSeparator(back3) || UTF8IsNEL(back3 + 1)) {
                                return true;
                        }
                }
                chBeforePrev = chPrev;
                chPrev = ch;
        }
        return false;
}

void CellBuffer::SetPerLine(PerLine *pl) {
        lv.SetPerLine(pl);
}

int CellBuffer::Lines() const {
        return lv.Lines();
}

int CellBuffer::LineStart(int line) const {
        if (line < 0)
                return 0;
        else if (line >= Lines())
                return Length();
        else
                return lv.LineStart(line);
}

bool CellBuffer::IsReadOnly() const {
        return readOnly;
}

void CellBuffer::SetReadOnly(bool set) {
        readOnly = set;
}

void CellBuffer::SetSavePoint() {
        uh.SetSavePoint();
}

bool CellBuffer::IsSavePoint() const {
        return uh.IsSavePoint();
}

void CellBuffer::TentativeStart() {
        uh.TentativeStart();
}

void CellBuffer::TentativeCommit() {
        uh.TentativeCommit();
}

int CellBuffer::TentativeSteps() {
        return uh.TentativeSteps();
}

bool CellBuffer::TentativeActive() const {
        return uh.TentativeActive();
}

// Without undo

void CellBuffer::InsertLine(int line, int position, bool lineStart) {
        lv.InsertLine(line, position, lineStart);
}

void CellBuffer::RemoveLine(int line) {
        lv.RemoveLine(line);
}

bool CellBuffer::UTF8LineEndOverlaps(int position) const {
        unsigned char bytes[] = {
                static_cast<unsigned char>(substance.ValueAt(position-2)),
                static_cast<unsigned char>(substance.ValueAt(position-1)),
                static_cast<unsigned char>(substance.ValueAt(position)),
                static_cast<unsigned char>(substance.ValueAt(position+1)),
        };
        return UTF8IsSeparator(bytes) || UTF8IsSeparator(bytes+1) || UTF8IsNEL(bytes+1);
}

void CellBuffer::ResetLineEnds() {
        // Reinitialize line data -- too much work to preserve
        lv.Init();

        int position = 0;
        int length = Length();
        int lineInsert = 1;
        bool atLineStart = true;
        lv.InsertText(lineInsert-1, length);
        unsigned char chBeforePrev = 0;
        unsigned char chPrev = 0;
        for (int i = 0; i < length; i++) {
                unsigned char ch = substance.ValueAt(position + i);
                if (ch == '\r') {
                        InsertLine(lineInsert, (position + i) + 1, atLineStart);
                        lineInsert++;
                } else if (ch == '\n') {
                        if (chPrev == '\r') {
                                // Patch up what was end of line
                                lv.SetLineStart(lineInsert - 1, (position + i) + 1);
                        } else {
                                InsertLine(lineInsert, (position + i) + 1, atLineStart);
                                lineInsert++;
                        }
                } else if (utf8LineEnds) {
                        unsigned char back3[3] = {chBeforePrev, chPrev, ch};
                        if (UTF8IsSeparator(back3) || UTF8IsNEL(back3+1)) {
                                InsertLine(lineInsert, (position + i) + 1, atLineStart);
                                lineInsert++;
                        }
                }
                chBeforePrev = chPrev;
                chPrev = ch;
        }
}

void CellBuffer::BasicInsertString(int position, const char *s, int insertLength) {
        if (insertLength == 0)
                return;
        PLATFORM_ASSERT(insertLength > 0);

        unsigned char chAfter = substance.ValueAt(position);
        bool breakingUTF8LineEnd = false;
        if (utf8LineEnds && UTF8IsTrailByte(chAfter)) {
                breakingUTF8LineEnd = UTF8LineEndOverlaps(position);
        }

        substance.InsertFromArray(position, s, 0, insertLength);
        style.InsertValue(position, insertLength, 0);

        int lineInsert = lv.LineFromPosition(position) + 1;
        bool atLineStart = lv.LineStart(lineInsert-1) == position;
        // Point all the lines after the insertion point further along in the buffer
        lv.InsertText(lineInsert-1, insertLength);
        unsigned char chBeforePrev = substance.ValueAt(position - 2);
        unsigned char chPrev = substance.ValueAt(position - 1);
        if (chPrev == '\r' && chAfter == '\n') {
                // Splitting up a crlf pair at position
                InsertLine(lineInsert, position, false);
                lineInsert++;
        }
        if (breakingUTF8LineEnd) {
                RemoveLine(lineInsert);
        }
        unsigned char ch = ' ';
        for (int i = 0; i < insertLength; i++) {
                ch = s[i];
                if (ch == '\r') {
                        InsertLine(lineInsert, (position + i) + 1, atLineStart);
                        lineInsert++;
                } else if (ch == '\n') {
                        if (chPrev == '\r') {
                                // Patch up what was end of line
                                lv.SetLineStart(lineInsert - 1, (position + i) + 1);
                        } else {
                                InsertLine(lineInsert, (position + i) + 1, atLineStart);
                                lineInsert++;
                        }
                } else if (utf8LineEnds) {
                        unsigned char back3[3] = {chBeforePrev, chPrev, ch};
                        if (UTF8IsSeparator(back3) || UTF8IsNEL(back3+1)) {
                                InsertLine(lineInsert, (position + i) + 1, atLineStart);
                                lineInsert++;
                        }
                }
                chBeforePrev = chPrev;
                chPrev = ch;
        }
        // Joining two lines where last insertion is cr and following substance starts with lf
        if (chAfter == '\n') {
                if (ch == '\r') {
                        // End of line already in buffer so drop the newly created one
                        RemoveLine(lineInsert - 1);
                }
        } else if (utf8LineEnds && !UTF8IsAscii(chAfter)) {
                // May have end of UTF-8 line end in buffer and start in insertion
                for (int j = 0; j < UTF8SeparatorLength-1; j++) {
                        unsigned char chAt = substance.ValueAt(position + insertLength + j);
                        unsigned char back3[3] = {chBeforePrev, chPrev, chAt};
                        if (UTF8IsSeparator(back3)) {
                                InsertLine(lineInsert, (position + insertLength + j) + 1, atLineStart);
                                lineInsert++;
                        }
                        if ((j == 0) && UTF8IsNEL(back3+1)) {
                                InsertLine(lineInsert, (position + insertLength + j) + 1, atLineStart);
                                lineInsert++;
                        }
                        chBeforePrev = chPrev;
                        chPrev = chAt;
                }
        }
}

void CellBuffer::BasicDeleteChars(int position, int deleteLength) {
        if (deleteLength == 0)
                return;

        if ((position == 0) && (deleteLength == substance.Length())) {
                // If whole buffer is being deleted, faster to reinitialise lines data
                // than to delete each line.
                lv.Init();
        } else {
                // Have to fix up line positions before doing deletion as looking at text in buffer
                // to work out which lines have been removed

                int lineRemove = lv.LineFromPosition(position) + 1;
                lv.InsertText(lineRemove-1, - (deleteLength));
                unsigned char chPrev = substance.ValueAt(position - 1);
                unsigned char chBefore = chPrev;
                unsigned char chNext = substance.ValueAt(position);
                bool ignoreNL = false;
                if (chPrev == '\r' && chNext == '\n') {
                        // Move back one
                        lv.SetLineStart(lineRemove, position);
                        lineRemove++;
                        ignoreNL = true;        // First \n is not real deletion
                }
                if (utf8LineEnds && UTF8IsTrailByte(chNext)) {
                        if (UTF8LineEndOverlaps(position)) {
                                RemoveLine(lineRemove);
                        }
                }

                unsigned char ch = chNext;
                for (int i = 0; i < deleteLength; i++) {
                        chNext = substance.ValueAt(position + i + 1);
                        if (ch == '\r') {
                                if (chNext != '\n') {
                                        RemoveLine(lineRemove);
                                }
                        } else if (ch == '\n') {
                                if (ignoreNL) {
                                        ignoreNL = false;       // Further \n are real deletions
                                } else {
                                        RemoveLine(lineRemove);
                                }
                        } else if (utf8LineEnds) {
                                if (!UTF8IsAscii(ch)) {
                                        unsigned char next3[3] = {ch, chNext,
                                                static_cast<unsigned char>(substance.ValueAt(position + i + 2))};
                                        if (UTF8IsSeparator(next3) || UTF8IsNEL(next3)) {
                                                RemoveLine(lineRemove);
                                        }
                                }
                        }

                        ch = chNext;
                }
                // May have to fix up end if last deletion causes cr to be next to lf
                // or removes one of a crlf pair
                char chAfter = substance.ValueAt(position + deleteLength);
                if (chBefore == '\r' && chAfter == '\n') {
                        // Using lineRemove-1 as cr ended line before start of deletion
                        RemoveLine(lineRemove - 1);
                        lv.SetLineStart(lineRemove - 1, position + 1);
                }
        }
        substance.DeleteRange(position, deleteLength);
        style.DeleteRange(position, deleteLength);
}

bool CellBuffer::SetUndoCollection(bool collectUndo) {
        collectingUndo = collectUndo;
        uh.DropUndoSequence();
        return collectingUndo;
}

bool CellBuffer::IsCollectingUndo() const {
        return collectingUndo;
}

void CellBuffer::BeginUndoAction() {
        uh.BeginUndoAction();
}

void CellBuffer::EndUndoAction() {
        uh.EndUndoAction();
}

void CellBuffer::AddUndoAction(int token, bool mayCoalesce) {
        bool startSequence;
        uh.AppendAction(containerAction, token, 0, 0, startSequence, mayCoalesce);
}

void CellBuffer::DeleteUndoHistory() {
        uh.DeleteUndoHistory();
}

bool CellBuffer::CanUndo() const {
        return uh.CanUndo();
}

int CellBuffer::StartUndo() {
        return uh.StartUndo();
}

const Action &CellBuffer::GetUndoStep() const {
        return uh.GetUndoStep();
}

void CellBuffer::PerformUndoStep() {
        const Action &actionStep = uh.GetUndoStep();
        if (actionStep.at == insertAction) {
                if (substance.Length() < actionStep.lenData) {
                        throw std::runtime_error(
                                "CellBuffer::PerformUndoStep: deletion must be less than document length.");
                }
                BasicDeleteChars(actionStep.position, actionStep.lenData);
        } else if (actionStep.at == removeAction) {
                BasicInsertString(actionStep.position, actionStep.data, actionStep.lenData);
        }
        uh.CompletedUndoStep();
}

bool CellBuffer::CanRedo() const {
        return uh.CanRedo();
}

int CellBuffer::StartRedo() {
        return uh.StartRedo();
}

const Action &CellBuffer::GetRedoStep() const {
        return uh.GetRedoStep();
}

void CellBuffer::PerformRedoStep() {
        const Action &actionStep = uh.GetRedoStep();
        if (actionStep.at == insertAction) {
                BasicInsertString(actionStep.position, actionStep.data, actionStep.lenData);
        } else if (actionStep.at == removeAction) {
                BasicDeleteChars(actionStep.position, actionStep.lenData);
        }
        uh.CompletedRedoStep();
}