Reorganize mdv and observe packages

pkg/observe/lib/src/compound_binding.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 observe;
+
+/** The callback used in the [CompoundBinding.combinator] field. */
+typedef Object CompoundBindingCombinator(Map objects);
+
+/**
+ * Model-Driven Views contains a helper object which is useful for the
+ * implementation of a Custom Syntax.
+ *
+ *     var binding = new CompoundBinding((values) {
+ *       var combinedValue;
+ *       // compute combinedValue based on the current values which are provided
+ *       return combinedValue;
+ *     });
+ *     binding.bind('name1', obj1, path1);
+ *     binding.bind('name2', obj2, path2);
+ *     //...
+ *     binding.bind('nameN', objN, pathN);
+ *
+ * CompoundBinding is an object which knows how to listen to multiple path
+ * values (registered via [bind]) and invoke its [combinator] when one or more
+ * of the values have changed and set its [value] property to the return value
+ * of the function. When any value has changed, all current values are provided
+ * to the [combinator] in the single `values` argument.
+ */
+// TODO(jmesserly): rename to something that indicates it's a computed value?
+class CompoundBinding extends ObservableBase {
+  CompoundBindingCombinator _combinator;
+
+  // TODO(jmesserly): ideally these would be String keys, but sometimes we
+  // use integers.
+  Map<dynamic, StreamSubscription> _bindings = new Map();
+  Map _values = new Map();
+  bool _scheduled = false;
+  bool _disposed = false;
+  Object _value;
+
+  CompoundBinding([CompoundBindingCombinator combinator]) {
+    // TODO(jmesserly): this is a tweak to the original code, it seemed to me
+    // that passing the combinator to the constructor should be equivalent to
+    // setting it via the property.
+    // I also added a null check to the combinator setter.
+    this.combinator = combinator;
+  }
+
+  CompoundBindingCombinator get combinator => _combinator;
+
+  set combinator(CompoundBindingCombinator combinator) {
+    _combinator = combinator;
+    if (combinator != null) _scheduleResolve();
+  }
+
+  static const _VALUE = const Symbol('value');
+
+  get value => _value;
+
+  void set value(newValue) {
+    _value = notifyPropertyChange(_VALUE, _value, newValue);
+  }
+
+  void bind(name, model, String path) {
+    unbind(name);
+
+    _bindings[name] = new PathObserver(model, path).bindSync((value) {
+      _values[name] = value;
+      _scheduleResolve();
+    });
+  }
+
+  void unbind(name, {bool suppressResolve: false}) {
+    var binding = _bindings.remove(name);
+    if (binding == null) return;
+
+    binding.cancel();
+    _values.remove(name);
+    if (!suppressResolve) _scheduleResolve();
+  }
+
+  // TODO(rafaelw): Is this the right processing model?
+  // TODO(rafaelw): Consider having a seperate ChangeSummary for
+  // CompoundBindings so to excess dirtyChecks.
+  void _scheduleResolve() {
+    if (_scheduled) return;
+    _scheduled = true;
+    queueChangeRecords(resolve);
+  }
+
+  void resolve() {
+    if (_disposed) return;
+    _scheduled = false;
+
+    if (_combinator == null) {
+      throw new StateError(
+          'CompoundBinding attempted to resolve without a combinator');
+    }
+
+    value = _combinator(_values);
+  }
+
+  void dispose() {
+    for (var binding in _bindings.values) {
+      binding.cancel();
+    }
+    _bindings.clear();
+    _values.clear();
+
+    _disposed = true;
+    value = null;
+  }
+}