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 "LocalAccessible-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   LocalAccessible* parent = mTextLeaf->LocalParent();
  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   mTextOffset = mHyperText->GetChildOffset(mTextLeaf);
  48   NS_ASSERTION(mTextOffset != -1, "Text leaf hasn't offset within hyper text!");
  49
  50   uint32_t oldLen = aOldText.Length(), newLen = aNewText.Length();
  51   uint32_t minLen = std::min(oldLen, newLen);
  52
  53   // Trim coinciding substrings from the end.
  54   uint32_t skipEnd = 0;
  55   while (minLen - skipEnd > aSkipStart &&
  56          aNewText[newLen - skipEnd - 1] == aOldText[oldLen - skipEnd - 1]) {
  57     skipEnd++;
  58   }
  59
  60   uint32_t strLen1 = oldLen - aSkipStart - skipEnd;
  61   uint32_t strLen2 = newLen - aSkipStart - skipEnd;
  62
  63   const nsAString& str1 = Substring(aOldText, aSkipStart, strLen1);
  64   const nsAString& str2 = Substring(aNewText, aSkipStart, strLen2);
  65
  66   // Increase offset of the text leaf on skipped characters amount.
  67   mTextOffset += aSkipStart;
  68
  69   // It could be single insertion or removal or the case of long strings. Do not
  70   // calculate the difference between long strings and prefer to fire pair of
  71   // insert/remove events as the old string was replaced on the new one.
  72   if (strLen1 == 0 || strLen2 == 0 || strLen1 > kMaxStrLen ||
  73       strLen2 > kMaxStrLen) {
  74     if (strLen1 > 0) {
  75       // Fire text change event for removal.
  76       RefPtr<AccEvent> textRemoveEvent =
  77           new AccTextChangeEvent(mHyperText, mTextOffset, str1, false);
  78       mDocument->FireDelayedEvent(textRemoveEvent);
  79     }
  80
  81     if (strLen2 > 0) {
  82       // Fire text change event for insertion.
  83       RefPtr<AccEvent> textInsertEvent =
  84           new AccTextChangeEvent(mHyperText, mTextOffset, str2, true);
  85       mDocument->FireDelayedEvent(textInsertEvent);
  86     }
  87
  88     mDocument->MaybeNotifyOfValueChange(mHyperText);
  89
  90     // Update the text.
  91     mTextLeaf->SetText(aNewText);
  92     mHyperText->InvalidateCachedHyperTextOffsets();
  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
 134   mDocument->MaybeNotifyOfValueChange(mHyperText);
 135
 136   // Update the text.
 137   mTextLeaf->SetText(aNewText);
 138   mHyperText->InvalidateCachedHyperTextOffsets();
 139 }
 140
 141 void TextUpdater::ComputeTextChangeEvents(
 142     const nsAString& aStr1, const nsAString& aStr2, uint32_t* aEntries,
 143     nsTArray<RefPtr<AccEvent> >& aEvents) {
 144   int32_t colIdx = aStr1.Length(), rowIdx = aStr2.Length();
 145
 146   // Point at which strings last matched.
 147   int32_t colEnd = colIdx;
 148   int32_t rowEnd = rowIdx;
 149
 150   int32_t colLen = colEnd + 1;
 151   uint32_t* row = aEntries + rowIdx * colLen;
 152   uint32_t dist = row[colIdx];  // current Levenshtein distance
 153   while (rowIdx && colIdx) {    // stop when we can't move diagonally
 154     if (aStr1[colIdx - 1] == aStr2[rowIdx - 1]) {  // match
 155       if (rowIdx < rowEnd) {  // deal with any pending insertion
 156         FireInsertEvent(Substring(aStr2, rowIdx, rowEnd - rowIdx), rowIdx,
 157                         aEvents);
 158       }
 159       if (colIdx < colEnd) {  // deal with any pending deletion
 160         FireDeleteEvent(Substring(aStr1, colIdx, colEnd - colIdx), rowIdx,
 161                         aEvents);
 162       }
 163
 164       colEnd = --colIdx;  // reset the match point
 165       rowEnd = --rowIdx;
 166       row -= colLen;
 167       continue;
 168     }
 169     --dist;
 170     if (dist == row[colIdx - 1 - colLen]) {  // substitution
 171       --colIdx;
 172       --rowIdx;
 173       row -= colLen;
 174       continue;
 175     }
 176     if (dist == row[colIdx - colLen]) {  // insertion
 177       --rowIdx;
 178       row -= colLen;
 179       continue;
 180     }
 181     if (dist == row[colIdx - 1]) {  // deletion
 182       --colIdx;
 183       continue;
 184     }
 185     MOZ_ASSERT_UNREACHABLE("huh?");
 186     return;
 187   }
 188
 189   if (rowEnd) FireInsertEvent(Substring(aStr2, 0, rowEnd), 0, aEvents);
 190   if (colEnd) FireDeleteEvent(Substring(aStr1, 0, colEnd), 0, aEvents);
 191 }