Make Sky's EditableText mostly work

sky/examples/editor/editable_string.dart

+// Copyright 2015 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+import 'package:sky/services/keyboard/keyboard.mojom.dart';
+
+typedef void StringChangedCallback(EditableString updated);
+
+class TextRange {
+  final int start;
+  final int end;
+
+  TextRange({this.start, this.end});
+  TextRange.collapsed(int position) : start = position, end = position;
+  const TextRange.empty() : start = -1, end = -1;
+
+  bool get isValid => start >= 0 && end >= 0;
+  bool get isCollapsed => start == end;
+}
+
+class EditableString implements KeyboardClient {
+  String text;
+  TextRange composing = const TextRange.empty();
+  TextRange selection = const TextRange.empty();
+
+  final StringChangedCallback onChanged;
+
+  KeyboardClientStub stub;
+
+  EditableString({this.text: '', this.onChanged}) {
+    stub = new KeyboardClientStub.unbound()..impl = this;
+  }
+
+  String textBefore(TextRange range) {
+    return text.substring(0, range.start);
+  }
+
+  String textAfter(TextRange range) {
+    return text.substring(range.end);
+  }
+
+  String textInside(TextRange range) {
+    return text.substring(range.start, range.end);
+  }
+
+  void _delete(TextRange range) {
+    if (range.isCollapsed || !range.isValid)
+      return;
+    text = textBefore(range) + textAfter(range);
+  }
+
+  // Returns the range of |newText| inside this string.
+  TextRange _replace(TextRange range, String newText) {
+    if (!range.isValid) {
+      int start = text.length;
+      int end = start + newText.length;
+      text += newText;

[eseidel, 2015/03/10 18:39:29]

You should make this more self-documenting.

+      return new TextRange(start: start, end: end);
+    }
+
+    String before = textBefore(range);
+    String after = textAfter(range);
+
+    text = before + newText + after;
+    return new TextRange(start: before.length,
+                         end: before.length + newText.length);
+  }
+
+  void commitCompletion(CompletionData completion) {
+    // TODO(abarth): Not implemented.
+  }
+
+  void commitCorrection(CorrectionData correction) {
+    // TODO(abarth): Not implemented.
+  }
+
+  void commitText(String text, int newCursorPosition) {
+    // TODO(abarth): Why is |newCursorPosition| always 1?
+    TextRange committedRange = _replace(composing, text);
+    selection = new TextRange.collapsed(committedRange.end);
+    composing = const TextRange.empty();
+    onChanged(this);
+  }
+
+  void deleteSurroundingText(int beforeLength, int afterLength) {
+    TextRange beforeRange = new TextRange(start: selection.start - beforeLength,
+                                          end: selection.start);
+    TextRange afterRange = new TextRange(start: selection.end,
+                                         end: selection.end + afterLength);
+    _delete(afterRange);
+    _delete(beforeRange);
+    selection = new TextRange(start: selection.start - beforeLength,
+                              end: selection.end - beforeLength);
+  }
+
+  void setComposingRegion(int start, int end) {
+    composing = new TextRange(start: start, end: end);
+    onChanged(this);
+  }
+
+  void setComposingText(String text, int newCursorPosition) {
+    // TODO(abarth): Why is |newCursorPosition| always 1?
+    composing = _replace(composing, text);
+    selection = new TextRange.collapsed(composing.end);
+    onChanged(this);
+  }
+
+  void setSelection(int start, int end) {
+    selection = new TextRange(start: start, end: end);
+  }
+}
+