accessible/base/TextUpdater.cpp

   1 /* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
   2 /* This Source Code Form is subject to the terms of the Mozilla Public
   3  * License, v. 2.0. If a copy of the MPL was not distributed with this
   4  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
   5
   6 #include "TextUpdater.h"
   7
   8 #include "Accessible-inl.h"
   9 #include "DocAccessible-inl.h"
  10 #include "TextLeafAccessible.h"
  11 #include <algorithm>
  12
  13 using namespace mozilla::a11y;
  14
  15 void TextUpdater::Run(DocAccessible* aDocument, TextLeafAccessible* aTextLeaf,
  16                       const nsAString& aNewText) {
  17   NS_ASSERTION(aTextLeaf, "No text leaf accessible?");
  18
  19   const nsString& oldText = aTextLeaf->Text();
  20   uint32_t oldLen = oldText.Length(), newLen = aNewText.Length();
  21   uint32_t minLen = std::min(oldLen, newLen);
  22
  23   // Skip coinciding begin substrings.
  24   uint32_t skipStart = 0;
  25   for (; skipStart < minLen; skipStart++) {
  26     if (aNewText[skipStart] != oldText[skipStart]) break;
  27   }
  28
  29   // The text was changed. Do update.
  30   if (skipStart != minLen || oldLen != newLen) {
  31     TextUpdater updater(aDocument, aTextLeaf);
  32     updater.DoUpdate(aNewText, oldText, skipStart);
  33   }
  34 }
  35
  36 void TextUpdater::DoUpdate(const nsAString& aNewText, const nsAString& aOldText,
  37                            uint32_t aSkipStart) {
  38   Accessible* parent = mTextLeaf->Parent();
  39   if (!parent) return;
  40
  41   mHyperText = parent->AsHyperText();
  42   if (!mHyperText) {
  43     MOZ_ASSERT_UNREACHABLE("Text leaf parent is not hypertext!");
  44     return;
  45   }
  46
  47   // Get the text leaf accessible offset and invalidate cached offsets after it.
  48   mTextOffset = mHyperText->GetChildOffset(mTextLeaf, true);
  49   NS_ASSERTION(mTextOffset != -1, "Text leaf hasn't offset within hyper text!");
  50
  51   uint32_t oldLen = aOldText.Length(), newLen = aNewText.Length();
  52   uint32_t minLen = std::min(oldLen, newLen);
  53
  54   // Trim coinciding substrings from the end.
  55   uint32_t skipEnd = 0;
  56   while (minLen - skipEnd > aSkipStart &&
  57          aNewText[newLen - skipEnd - 1] == aOldText[oldLen - skipEnd - 1]) {
  58     skipEnd++;
  59   }
  60
  61   uint32_t strLen1 = oldLen - aSkipStart - skipEnd;
  62   uint32_t strLen2 = newLen - aSkipStart - skipEnd;
  63
  64   const nsAString& str1 = Substring(aOldText, aSkipStart, strLen1);
  65   const nsAString& str2 = Substring(aNewText, aSkipStart, strLen2);
  66
  67   // Increase offset of the text leaf on skipped characters amount.
  68   mTextOffset += aSkipStart;
  69
  70   // It could be single insertion or removal or the case of long strings. Do not
  71   // calculate the difference between long strings and prefer to fire pair of
  72   // insert/remove events as the old string was replaced on the new one.
  73   if (strLen1 == 0 || strLen2 == 0 || strLen1 > kMaxStrLen ||
  74       strLen2 > kMaxStrLen) {
  75     if (strLen1 > 0) {
  76       // Fire text change event for removal.
  77       RefPtr<AccEvent> textRemoveEvent =
  78           new AccTextChangeEvent(mHyperText, mTextOffset, str1, false);
  79       mDocument->FireDelayedEvent(textRemoveEvent);
  80     }
  81
  82     if (strLen2 > 0) {
  83       // Fire text change event for insertion.
  84       RefPtr<AccEvent> textInsertEvent =
  85           new AccTextChangeEvent(mHyperText, mTextOffset, str2, true);
  86       mDocument->FireDelayedEvent(textInsertEvent);
  87     }
  88
  89     mDocument->MaybeNotifyOfValueChange(mHyperText);
  90
  91     // Update the text.
  92     mTextLeaf->SetText(aNewText);
  93     return;
  94   }
  95
  96   // Otherwise find the difference between strings and fire events.
  97   // Note: we can skip initial and final coinciding characters since they don't
  98   // affect the Levenshtein distance.
  99
 100   // Compute the flat structured matrix need to compute the difference.
 101   uint32_t len1 = strLen1 + 1, len2 = strLen2 + 1;
 102   uint32_t* entries = new uint32_t[len1 * len2];
 103
 104   for (uint32_t colIdx = 0; colIdx < len1; colIdx++) entries[colIdx] = colIdx;
 105
 106   uint32_t* row = entries;
 107   for (uint32_t rowIdx = 1; rowIdx < len2; rowIdx++) {
 108     uint32_t* prevRow = row;
 109     row += len1;
 110     row[0] = rowIdx;
 111     for (uint32_t colIdx = 1; colIdx < len1; colIdx++) {
 112       if (str1[colIdx - 1] != str2[rowIdx - 1]) {
 113         uint32_t left = row[colIdx - 1];
 114         uint32_t up = prevRow[colIdx];
 115         uint32_t upleft = prevRow[colIdx - 1];
 116         row[colIdx] = std::min(upleft, std::min(left, up)) + 1;
 117       } else {
 118         row[colIdx] = prevRow[colIdx - 1];
 119       }
 120     }
 121   }
 122
 123   // Compute events based on the difference.
 124   nsTArray<RefPtr<AccEvent> > events;
 125   ComputeTextChangeEvents(str1, str2, entries, events);
 126
 127   delete[] entries;
 128
 129   // Fire events.
 130   for (int32_t idx = events.Length() - 1; idx >= 0; idx--)
 131     mDocument->FireDelayedEvent(events[idx]);
 132
 133   mDocument->MaybeNotifyOfValueChange(mHyperText);
 134
 135   // Update the text.
 136   mTextLeaf->SetText(aNewText);
 137 }
 138
 139 void TextUpdater::ComputeTextChangeEvents(
 140     const nsAString& aStr1, const nsAString& aStr2, uint32_t* aEntries,
 141     nsTArray<RefPtr<AccEvent> >& aEvents) {
 142   int32_t colIdx = aStr1.Length(), rowIdx = aStr2.Length();
 143
 144   // Point at which strings last matched.
 145   int32_t colEnd = colIdx;
 146   int32_t rowEnd = rowIdx;
 147
 148   int32_t colLen = colEnd + 1;
 149   uint32_t* row = aEntries + rowIdx * colLen;
 150   uint32_t dist = row[colIdx];  // current Levenshtein distance
 151   while (rowIdx && colIdx) {    // stop when we can't move diagonally
 152     if (aStr1[colIdx - 1] == aStr2[rowIdx - 1]) {  // match
 153       if (rowIdx < rowEnd) {  // deal with any pending insertion
 154         FireInsertEvent(Substring(aStr2, rowIdx, rowEnd - rowIdx), rowIdx,
 155                         aEvents);
 156       }
 157       if (colIdx < colEnd) {  // deal with any pending deletion
 158         FireDeleteEvent(Substring(aStr1, colIdx, colEnd - colIdx), rowIdx,
 159                         aEvents);
 160       }
 161
 162       colEnd = --colIdx;  // reset the match point
 163       rowEnd = --rowIdx;
 164       row -= colLen;
 165       continue;
 166     }
 167     --dist;
 168     if (dist == row[colIdx - 1 - colLen]) {  // substitution
 169       --colIdx;
 170       --rowIdx;
 171       row -= colLen;
 172       continue;
 173     }
 174     if (dist == row[colIdx - colLen]) {  // insertion
 175       --rowIdx;
 176       row -= colLen;
 177       continue;
 178     }
 179     if (dist == row[colIdx - 1]) {  // deletion
 180       --colIdx;
 181       continue;
 182     }
 183     MOZ_ASSERT_UNREACHABLE("huh?");
 184     return;
 185   }
 186
 187   if (rowEnd) FireInsertEvent(Substring(aStr2, 0, rowEnd), 0, aEvents);
 188   if (colEnd) FireDeleteEvent(Substring(aStr1, 0, colEnd), 0, aEvents);
 189 }