/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */

/* This Source Code Form is subject to the terms of the Mozilla Public

 * License, v. 2.0. If a copy of the MPL was not distributed with this

 * file, You can obtain one at http://mozilla.org/MPL/2.0/. */

#include "TextUpdater.h"

#include "Accessible-inl.h"

#include "DocAccessible-inl.h"

#include "TextLeafAccessible.h"

#include <algorithm>

using namespace mozilla::a11y;

void

TextUpdater::Run(DocAccessible* aDocument, TextLeafAccessible* aTextLeaf,

                 const nsAString& aNewText)

{

  NS_ASSERTION(aTextLeaf, "No text leaf accessible?");

  const nsString& oldText = aTextLeaf->Text();

  uint32_t oldLen = oldText.Length(), newLen = aNewText.Length();

  uint32_t minLen = std::min(oldLen, newLen);

  // Skip coinciding begin substrings.

  uint32_t skipStart = 0;

  for (; skipStart < minLen; skipStart++) {

    if (aNewText[skipStart] != oldText[skipStart])

      break;

  }

  // The text was changed. Do update.

  if (skipStart != minLen || oldLen != newLen) {

    TextUpdater updater(aDocument, aTextLeaf);

    updater.DoUpdate(aNewText, oldText, skipStart);

  }

}

void

TextUpdater::DoUpdate(const nsAString& aNewText, const nsAString& aOldText,

                      uint32_t aSkipStart)

{

  Accessible* parent = mTextLeaf->Parent();

  if (!parent)

    return;

  mHyperText = parent->AsHyperText();

  if (!mHyperText) {

    MOZ_ASSERT_UNREACHABLE("Text leaf parent is not hypertext!");

    return;

  }

  // Get the text leaf accessible offset and invalidate cached offsets after it.

  mTextOffset = mHyperText->GetChildOffset(mTextLeaf, true);

  NS_ASSERTION(mTextOffset != -1,

               "Text leaf hasn't offset within hyper text!");

  uint32_t oldLen = aOldText.Length(), newLen = aNewText.Length();

  uint32_t minLen = std::min(oldLen, newLen);

  // Trim coinciding substrings from the end.

  uint32_t skipEnd = 0;

  while (minLen - skipEnd > aSkipStart &&

         aNewText[newLen - skipEnd - 1] == aOldText[oldLen - skipEnd - 1]) {

    skipEnd++;

  }

  uint32_t strLen1 = oldLen - aSkipStart - skipEnd;

  uint32_t strLen2 = newLen - aSkipStart - skipEnd;

  const nsAString& str1 = Substring(aOldText, aSkipStart, strLen1);

  const nsAString& str2 = Substring(aNewText, aSkipStart, strLen2);

  // Increase offset of the text leaf on skipped characters amount.

  mTextOffset += aSkipStart;

  // It could be single insertion or removal or the case of long strings. Do not

  // calculate the difference between long strings and prefer to fire pair of

  // insert/remove events as the old string was replaced on the new one.

  if (strLen1 == 0 || strLen2 == 0 ||

      strLen1 > kMaxStrLen || strLen2 > kMaxStrLen) {

    if (strLen1 > 0) {

      // Fire text change event for removal.

      RefPtr<AccEvent> textRemoveEvent =

        new AccTextChangeEvent(mHyperText, mTextOffset, str1, false);

      mDocument->FireDelayedEvent(textRemoveEvent);

    }

    if (strLen2 > 0) {

      // Fire text change event for insertion.

      RefPtr<AccEvent> textInsertEvent =

        new AccTextChangeEvent(mHyperText, mTextOffset, str2, true);

      mDocument->FireDelayedEvent(textInsertEvent);

    }

    mDocument->MaybeNotifyOfValueChange(mHyperText);

    // Update the text.

    mTextLeaf->SetText(aNewText);

    return;

  }

  // Otherwise find the difference between strings and fire events.

  // Note: we can skip initial and final coinciding characters since they don't

  // affect the Levenshtein distance.

  // Compute the flat structured matrix need to compute the difference.

  uint32_t len1 = strLen1 + 1, len2 = strLen2 + 1;

  uint32_t* entries = new uint32_t[len1 * len2];

  for (uint32_t colIdx = 0; colIdx < len1; colIdx++)

    entries[colIdx] = colIdx;

  uint32_t* row = entries;

  for (uint32_t rowIdx = 1; rowIdx < len2; rowIdx++) {

    uint32_t* prevRow = row;

    row += len1;

    row[0] = rowIdx;

    for (uint32_t colIdx = 1; colIdx < len1; colIdx++) {

      if (str1[colIdx - 1] != str2[rowIdx - 1]) {

        uint32_t left = row[colIdx - 1];

        uint32_t up = prevRow[colIdx];

        uint32_t upleft = prevRow[colIdx - 1];

        row[colIdx] = std::min(upleft, std::min(left, up)) + 1;

      } else {

        row[colIdx] = prevRow[colIdx - 1];

      }

    }

  }

  // Compute events based on the difference.

  nsTArray<RefPtr<AccEvent> > events;

  ComputeTextChangeEvents(str1, str2, entries, events);

  delete [] entries;

  // Fire events.

  for (int32_t idx = events.Length() - 1; idx >= 0; idx--)

    mDocument->FireDelayedEvent(events[idx]);

  mDocument->MaybeNotifyOfValueChange(mHyperText);

  // Update the text.

  mTextLeaf->SetText(aNewText);

}

void

TextUpdater::ComputeTextChangeEvents(const nsAString& aStr1,

                                     const nsAString& aStr2,

                                     uint32_t* aEntries,

                                     nsTArray<RefPtr<AccEvent> >& aEvents)

{

  int32_t colIdx = aStr1.Length(), rowIdx = aStr2.Length();

  // Point at which strings last matched.

  int32_t colEnd = colIdx;

  int32_t rowEnd = rowIdx;

  int32_t colLen = colEnd + 1;

  uint32_t* row = aEntries + rowIdx * colLen;

  uint32_t dist = row[colIdx]; // current Levenshtein distance

  while (rowIdx && colIdx) { // stop when we can't move diagonally

    if (aStr1[colIdx - 1] == aStr2[rowIdx - 1]) { // match

      if (rowIdx < rowEnd) { // deal with any pending insertion

        FireInsertEvent(Substring(aStr2, rowIdx, rowEnd - rowIdx),

                        rowIdx, aEvents);

      }

      if (colIdx < colEnd) { // deal with any pending deletion

        FireDeleteEvent(Substring(aStr1, colIdx, colEnd - colIdx),

                        rowIdx, aEvents);

      }

      colEnd = --colIdx; // reset the match point

      rowEnd = --rowIdx;

      row -= colLen;

      continue;

    }

    --dist;

    if (dist == row[colIdx - 1 - colLen]) { // substitution

      --colIdx;

      --rowIdx;

      row -= colLen;

      continue;

    }

    if (dist == row[colIdx - colLen]) { // insertion

      --rowIdx;

      row -= colLen;

      continue;

    }

    if (dist == row[colIdx - 1]) { // deletion

      --colIdx;

      continue;

    }

    MOZ_ASSERT_UNREACHABLE("huh?");

    return;

  }

  if (rowEnd)

    FireInsertEvent(Substring(aStr2, 0, rowEnd), 0, aEvents);

  if (colEnd)

    FireDeleteEvent(Substring(aStr1, 0, colEnd), 0, aEvents);

}