move polymer.dart into dart svn

pkg/polymer/lib/observe.dart

+// Copyright (c) 2013, 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.
+
+/**
+ * Helpers for observable objects.
+ * Intended for use with `package:observe`.
+ */
+library polymer.observe;
+
+import 'dart:async';
+import 'package:observe/observe.dart';
+
+const _VALUE = const Symbol('value');
+
+/**
+ * Forwards an observable property from one object to another. For example:
+ *
+ *     class MyModel extends ObservableBase {
+ *       StreamSubscription _sub;
+ *       MyOtherModel _otherModel;
+ *
+ *       MyModel() {
+ *         ...
+ *         _sub = bindProperty(_otherModel, const Symbol('value'),
+ *             () => notifyProperty(this, const Symbol('prop'));
+ *       }
+ *
+ *       String get prop => _otherModel.value;
+ *       set prop(String value) { _otherModel.value = value; }
+ *     }
+ *
+ * See also [notifyProperty].
+ */
+StreamSubscription bindProperty(Observable source, Symbol sourceName,
+    void callback()) {
+  return source.changes.listen((records) {
+    for (var record in records) {
+      if (record.changes(sourceName)) {
+        callback();
+      }
+    }
+  });
+}
+
+/**
+ * Notify the property change. Shorthand for:
+ *
+ *     target.notifyChange(new PropertyChangeRecord(targetName));
+ */
+void notifyProperty(Observable target, Symbol targetName) {
+  target.notifyChange(new PropertyChangeRecord(targetName));
+}
+
+
+// Inspired by ArrayReduction at:
+// https://raw.github.com/rafaelw/ChangeSummary/master/util/array_reduction.js
+// The main difference is we support anything on the rich Dart Iterable API.
+
+/**
+ * Observes a path starting from each item in the list.
+ */
+class ListPathObserver<E, P> extends ChangeNotifierBase {
+  final ObservableList<E> list;
+  final String _itemPath;
+  final List<PathObserver> _observers = <PathObserver>[];
+  final List<StreamSubscription> _subs = <StreamSubscription>[];
+  StreamSubscription _sub;
+  bool _scheduled = false;
+  Iterable<P> _value;
+
+  ListPathObserver(this.list, String path)
+      : _itemPath = path {
+
+    _sub = list.changes.listen((records) {
+      for (var record in records) {
+        if (record is ListChangeRecord) {
+          _observeItems(record.addedCount - record.removedCount);
+        }
+      }
+      _scheduleReduce(null);
+    });
+
+    _observeItems(list.length);
+    _reduce();
+  }
+
+  Iterable<P> get value => _value;
+
+  void dispose() {
+    if (_sub != null) _sub.cancel();
+    _subs.forEach((s) => s.cancel());
+    _subs.clear();
+  }
+
+  void _reduce() {
+    _scheduled = false;
+    _value = _observers.map((o) => o.value);
+    notifyChange(new PropertyChangeRecord(_VALUE));
+  }
+
+  void _scheduleReduce(_) {
+    if (_scheduled) return;
+    _scheduled = true;
+    runAsync(_reduce);
+  }
+
+  void _observeItems(int lengthAdjust) {
+    if (lengthAdjust > 0) {
+      for (int i = 0; i < lengthAdjust; i++) {
+        int len = _observers.length;
+        var pathObs = new PathObserver(list, '$len.$_itemPath');
+        _subs.add(pathObs.changes.listen(_scheduleReduce));
+        _observers.add(pathObs);
+      }
+    } else if (lengthAdjust < 0) {
+      for (int i = 0; i < -lengthAdjust; i++) {
+        _subs.removeLast().cancel();
+      }
+      int len = _observers.length;
+      _observers.removeRange(len + lengthAdjust, len);
+    }
+  }
+}