Port of github.com/polymer/polymer.

pkg/custom_element/lib/src/attribute_map.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.
+
+part of custom_element;
+
+/**
+ * Represents an attribute map of model values. If any items are added,
+ * removed, or replaced, then observers that are listening to [changes]
+ * will be notified.
+ */
+class _AttributeMap implements Map<String, String> {
+  final CustomElement _element;
+  final Map<String, String> _map;
+
+  /** Creates an attribute map wrapping the host attributes. */
+  _AttributeMap(CustomElement element)
+      : _element = element, _map = element.host.attributes;
+
+  // Forward all read methods:
+  Iterable<String> get keys => _map.keys;
+  Iterable<String> get values => _map.values;
+  int get length =>_map.length;
+  bool get isEmpty => _map.isEmpty;
+  bool get isNotEmpty => _map.isNotEmpty;
+  bool containsValue(Object value) => _map.containsValue(value);
+  bool containsKey(Object key) => _map.containsKey(key);
+  String operator [](Object key) => _map[key];
+  void forEach(void f(String key, String value)) => _map.forEach(f);
+  String toString() => _map.toString();
+
+  // Override the write methods and ensure attributeChanged is called:
+  void operator []=(String key, String value) {
+    int len = _map.length;
+    String oldValue = _map[key];
+    _map[key] = value;
+    if (len != _map.length || !identical(oldValue, value)) {
+      _element.attributeChanged(key, oldValue);
+    }
+  }
+
+  void addAll(Map<String, String> other) {
+    other.forEach((String key, String value) { this[key] = value; });
+  }
+
+  String putIfAbsent(String key, String ifAbsent()) {
+    int len = _map.length;
+    String result = _map.putIfAbsent(key, ifAbsent);
+    if (len != _map.length) {
+      _element.attributeChanged(key, null);
+    }
+    return result;
+  }
+
+  String remove(Object key) {
+    int len = _map.length;
+    String result =  _map.remove(key);
+    if (len != _map.length) {
+      _element.attributeChanged(key, result);
+    }
+    return result;
+  }
+
+  void clear() {
+    int len = _map.length;
+    if (len > 0) {
+      _map.forEach((key, value) {
+        _element.attributeChanged(key, value);
+      });
+    }
+    _map.clear();
+  }
+
+  /**
+   * This is not a [Map] method. We use it to implement "set attributes", which
+   * is a global replace operation. Rather than [clear] followed by [addAll],
+   * we try to be a bit smarter.
+   */
+  void _replaceAll(Map<String, String> other) {
+    for (var key in keys) {
+      if (!other.containsKey(key)) remove(key);
+    }
+    addAll(other);
+  }
+}