1 files changed, 215 insertions, 0 deletions
diff --git a/accessible/base/TextUpdater.cpp b/accessible/base/TextUpdater.cpp
new file mode 100644
index 0000000000..29f8ac11f3
--- /dev/null
+++ b/accessible/base/TextUpdater.cpp
@@ -0,0 +1,215 @@
+/* -*- 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 "CacheConstants.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);
+    aDocument->QueueCacheUpdate(aTextLeaf, CacheDomain::Text);
+  }
+}
+
+void TextUpdater::DoUpdate(const nsAString& aNewText, const nsAString& aOldText,
+                           uint32_t aSkipStart) {
+  LocalAccessible* parent = mTextLeaf->LocalParent();
+  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!");
+
+  // Don't bother diffing if the hypertext isn't editable. Diffing non-editable
+  // text can lead to weird screen reader results with live regions, e.g.,
+  // changing "text" to "testing" might read the diff "s ing" when we'd really
+  // just like to hear "testing."
+  if (!mHyperText->IsEditable()) {
+    // Fire text change event for removal.
+    RefPtr<AccEvent> textRemoveEvent =
+        new AccTextChangeEvent(mHyperText, mTextOffset, aOldText, false);
+    mDocument->FireDelayedEvent(textRemoveEvent);
+
+    // Fire text change event for insertion if there's text to insert.
+    if (!aNewText.IsEmpty()) {
+      RefPtr<AccEvent> textInsertEvent =
+          new AccTextChangeEvent(mHyperText, mTextOffset, aNewText, true);
+      mDocument->FireDelayedEvent(textInsertEvent);
+    }
+
+    mDocument->MaybeNotifyOfValueChange(mHyperText);
+
+    // Update the text.
+    mTextLeaf->SetText(aNewText);
+    return;
+  }
+
+  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);
+}