Bug 1901466: Implement ITextRangeProvider::FindText, r=Jamie

This revision implements ITextRangeProvider::FindText on UiaTextRange.
The function searches for a given string in the text range, forwards or
backwards, case-sensitive or not. The algorithm to do so uses a single
pass to build the range's text string plus an acceleration structure for
lookup later. It then calls Find (or RFind) on the maybe-lowercased
string before using that resulting index to binary search the
acceleration structure for the proper start and end indices of the
search string. Once it has those associated Accessibles, it builds a
text range and returns it.

This revision also implements tests for this functionality.

Differential Revision: https://phabricator.services.mozilla.com/D236304

accessible/windows/uia/UiaTextRange.cpp

@@ -463,7 +463,82 @@ UiaTextRange::FindAttribute(TEXTATTRIBUTEID aAttributeId, VARIANT aVal,
 STDMETHODIMP
 UiaTextRange::FindText(__RPC__in BSTR aText, BOOL aBackward, BOOL aIgnoreCase,
                        __RPC__deref_out_opt ITextRangeProvider** aRetVal) {
-  return E_NOTIMPL;
+  if (!aRetVal) {
+    return E_INVALIDARG;
+  }
+  *aRetVal = nullptr;
+  TextLeafRange range = GetRange();
+  if (!range) {
+    return CO_E_OBJNOTCONNECTED;
+  }
+  MOZ_ASSERT(range.Start() <= range.End(), "Range must be valid to proceed.");
+
+  // We can't find anything in an empty range.
+  if (range.Start() == range.End()) {
+    return S_OK;
+  }
+
+  // Iterate over the range's leaf segments and append each leaf's text. Keep
+  // track of the indices in the built string, associating them with the
+  // Accessible pointer whose text begins at that index.
+  nsTArray<std::pair<int32_t, Accessible*>> indexToAcc;
+  nsAutoString rangeText;
+  for (const TextLeafRange leafSegment : range) {
+    Accessible* startAcc = leafSegment.Start().mAcc;
+    MOZ_ASSERT(startAcc, "Start acc of leaf segment was unexpectedly null.");
+    indexToAcc.EmplaceBack(rangeText.Length(), startAcc);
+    startAcc->AppendTextTo(rangeText);
+  }
+
+  // Find the search string's start position in the text of the range, ignoring
+  // case if requested.
+  const nsDependentString searchStr{aText};
+  const int32_t startIndex = [&]() {
+    if (aIgnoreCase) {
+      ToLowerCase(rangeText);
+      nsAutoString searchStrLower;
+      ToLowerCase(searchStr, searchStrLower);
+      return aBackward ? rangeText.RFind(searchStrLower)
+                       : rangeText.Find(searchStrLower);
+    } else {
+      return aBackward ? rangeText.RFind(searchStr) : rangeText.Find(searchStr);
+    }
+  }();
+  if (startIndex == kNotFound) {
+    return S_OK;
+  }
+  const int32_t endIndex = startIndex + searchStr.Length();
+
+  // Binary search for the (index, Accessible*) pair where the index is as large
+  // as possible without exceeding the size of the search index. The associated
+  // Accessible* is the Accessible for the resulting TextLeafPoint.
+  auto GetNearestAccLessThanIndex = [&indexToAcc](int32_t aIndex) {
+    MOZ_ASSERT(aIndex >= 0, "Search index is less than 0.");
+    auto itr =
+        std::lower_bound(indexToAcc.begin(), indexToAcc.end(), aIndex,
+                         [](const std::pair<int32_t, Accessible*>& aPair,
+                            int32_t aIndex) { return aPair.first <= aIndex; });
+    MOZ_ASSERT(itr != indexToAcc.begin(),
+               "Iterator is unexpectedly at the beginning.");
+    --itr;
+    return itr;
+  };
+
+  // Calculate the TextLeafPoint for the start and end of the found text.
+  auto itr = GetNearestAccLessThanIndex(startIndex);
+  Accessible* foundTextStart = itr->second;
+  const int32_t offsetFromStart = startIndex - itr->first;
+  const TextLeafPoint rangeStart{foundTextStart, offsetFromStart};
+
+  itr = GetNearestAccLessThanIndex(endIndex);
+  Accessible* foundTextEnd = itr->second;
+  const int32_t offsetFromEndAccStart = endIndex - itr->first;
+  const TextLeafPoint rangeEnd{foundTextEnd, offsetFromEndAccStart};
+
+  TextLeafRange resultRange{rangeStart, rangeEnd};
+  RefPtr uiaRange = new UiaTextRange(resultRange);
+  uiaRange.forget(aRetVal);
+  return S_OK;
 }
 
 template <TEXTATTRIBUTEID Attr>