Refactor code to prepare for line-based tokenization.

dart/site/try/src/selection.dart

 // Copyright (c) 2014, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 library trydart.selection;
 
 import 'dart:html' show
     CharacterData,
     Node,
     NodeFilter,
     Selection,
     Text,
     TreeWalker;
 
 import 'decoration.dart';
 
 class TrySelection {
   final Node root;
-  final String text;
-  final int globalOffset;
-
   Node anchorNode;
   int anchorOffset;
 
-  TrySelection.internal(
-      this.root, this.text, this.globalOffset,
-      this.anchorNode, this.anchorOffset);
+  String text;
+  int globalOffset = -1;
 
-  factory TrySelection(Node root, Selection selection, String text) {
-    if (selection.isCollapsed) {
-      Node anchorNode = selection.anchorNode;
-      int anchorOffset = selection.anchorOffset;
-      return new TrySelection.internal(
-          root, text, computeGlobalOffset(root, anchorNode, anchorOffset),
-          anchorNode, anchorOffset);
-    } else {
-      return new TrySelection.internal(root, text, -1, null, -1);
-    }
-  }
+  TrySelection(this.root, Selection selection)
+      : this.anchorNode = selection.isCollapsed ? selection.anchorNode : null,
+        this.anchorOffset = selection.isCollapsed ? selection.anchorOffset : -1;
 
   Text addNodeFromSubstring(int start,
                             int end,
                             List<Node> nodes,
                             [Decoration decoration]) {
     if (start == end) return null;
 
     Text textNode = new Text(text.substring(start, end));
 
     if (start <= globalOffset && globalOffset < end) {
       anchorNode = textNode;
       anchorOffset = globalOffset - start;
     }
 
     nodes.add(decoration == null ? textNode : decoration.applyTo(textNode));
 
     return textNode;
   }
 
   void adjust(Selection selection) {
     if (anchorOffset >= 0) {
       selection.collapse(anchorNode, anchorOffset);
     }
   }
 
+  void updateText(String newText) {
+    text = newText;
+    globalOffset = computeGlobalOffset(root, anchorNode, anchorOffset);
+  }
+
   /// Computes the global offset, that is, the offset from [root].
   static int computeGlobalOffset(Node root, Node anchorNode, int anchorOffset) {
     if (anchorOffset == -1) return -1;
 
     int offset = 0;
     TreeWalker walker = new TreeWalker(root, NodeFilter.SHOW_TEXT);
     for (Node node = walker.nextNode();
          node != null;
          node = walker.nextNode()) {
       CharacterData text = node;
       if (anchorNode == text) {
         return anchorOffset + offset;
       }
       offset += text.data.length;
     }
 
     return -1;
   }
 }