Reorganize mdv and observe packages

sdk/lib/mdv_observe_impl/mdv_observe_impl.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.
-
-// This library itself is undocumented and not supported for end use.
-// Because dart:html must use some of this functionality, it has to be available
-// via a dart:* library. The public APIs are reexported via package:mdv_observe.
-// Generally we try to keep this library minimal, with utility types and
-// functions in the package.
-library dart.mdv_observe_impl;
-
-import 'dart:async';
-import 'dart:collection';
-
-part 'path_observer.dart';
-
-/**
- * Interface representing an observable object. This is used by data in
- * model-view architectures to notify interested parties of [changes].
- *
- * This object does not require any specific technique to implement
- * observability.
- *
- * You can use [ObservableMixin] as a base class or mixin to implement this.
- */
-abstract class Observable {
-  /**
-   * The stream of change records to this object.
-   *
-   * Changes should be delivered in asynchronous batches by calling
-   * [queueChangeRecords].
-   *
-   * [deliverChangeRecords] can be called to force delivery.
-   */
-  Stream<List<ChangeRecord>> get changes;
-
-  // TODO(jmesserly): remove these ASAP.
-  /**
-   * *Warning*: this method is temporary until dart2js supports mirrors.
-   * Gets the value of a field or index. This should return null if it was
-   * not found.
-   */
-  getValueWorkaround(key);
-
-  /**
-   * *Warning*: this method is temporary until dart2js supports mirrors.
-   * Sets the value of a field or index. This should have no effect if the field
-   * was not found.
-   */
-  void setValueWorkaround(key, Object value);
-}
-
-/**
- * Base class implementing [Observable].
- *
- * When a field, property, or indexable item is changed, a derived class should
- * call [notifyPropertyChange]. See that method for an example.
- */
-typedef ObservableBase = Object with ObservableMixin;
-
-/**
- * Mixin for implementing [Observable] objects.
- *
- * When a field, property, or indexable item is changed, a derived class should
- * call [notifyPropertyChange]. See that method for an example.
- */
-abstract class ObservableMixin implements Observable {
-  StreamController _broadcastController;
-  List<ChangeRecord> _changes;
-
-  Stream<List<ChangeRecord>> get changes {
-    if (_broadcastController == null) {
-      _broadcastController =
-          new StreamController<List<ChangeRecord>>.broadcast(sync: true);
-    }
-    return _broadcastController.stream;
-  }
-
-  void _deliverChanges() {
-    var changes = _changes;
-    _changes = null;
-    if (hasObservers && changes != null) {
-      // TODO(jmesserly): make "changes" immutable
-      _broadcastController.add(changes);
-    }
-  }
-
-  /**
-   * True if this object has any observers, and should call
-   * [notifyPropertyChange] for changes.
-   */
-  bool get hasObservers => _broadcastController != null &&
-                           _broadcastController.hasListener;
-
-  /**
-   * Notify that the field [name] of this object has been changed.
-   *
-   * The [oldValue] and [newValue] are also recorded. If the two values are
-   * identical, no change will be recorded.
-   *
-   * For convenience this returns [newValue]. This makes it easy to use in a
-   * setter:
-   *
-   *     var _myField;
-   *     get myField => _myField;
-   *     set myField(value) {
-   *       _myField = notifyPropertyChange(
-   *           const Symbol('myField'), _myField, value);
-   *     }
-   */
-  // TODO(jmesserly): should this be == instead of identical, to prevent
-  // spurious loops?
-  notifyPropertyChange(Symbol field, Object oldValue, Object newValue) {
-    if (hasObservers && !identical(oldValue, newValue)) {
-      notifyChange(new PropertyChangeRecord(field));
-    }
-    return newValue;
-  }
-
-  /**
-   * Notify observers of a change. For most objects [notifyPropertyChange] is
-   * more convenient, but collections sometimes deliver other types of changes
-   * such as a [ListChangeRecord].
-   */
-  void notifyChange(ChangeRecord record) {
-    if (!hasObservers) return;
-
-    if (_changes == null) {
-      _changes = [];
-      queueChangeRecords(_deliverChanges);
-    }
-    _changes.add(record);
-  }
-}
-
-
-/** Records a change to an [Observable]. */
-abstract class ChangeRecord {
-  /** True if the change affected the given item, otherwise false. */
-  bool change(key);
-}
-
-/** A change record to a field of an observable object. */
-class PropertyChangeRecord extends ChangeRecord {
-  /** The field that was changed. */
-  final Symbol field;
-
-  PropertyChangeRecord(this.field);
-
-  bool changes(key) => key is Symbol && field == key;
-
-  String toString() => '#<PropertyChangeRecord $field>';
-}
-
-/** A change record for an observable list. */
-class ListChangeRecord extends ChangeRecord {
-  /** The starting index of the change. */
-  final int index;
-
-  /** The number of items removed. */
-  final int removedCount;
-
-  /** The number of items added. */
-  final int addedCount;
-
-  ListChangeRecord(this.index, {this.removedCount: 0, this.addedCount: 0}) {
-    if (addedCount == 0 && removedCount == 0) {
-      throw new ArgumentError('added and removed counts should not both be '
-          'zero. Use 1 if this was a single item update.');
-    }
-  }
-
-  /** Returns true if the provided index was changed by this operation. */
-  bool changes(key) {
-    // If key isn't an int, or before the index, then it wasn't changed.
-    if (key is! int || key < index) return false;
-
-    // If this was a shift operation, anything after index is changed.
-    if (addedCount != removedCount) return true;
-
-    // Otherwise, anything in the update range was changed.
-    return key < index + addedCount;
-  }
-
-  String toString() => '#<ListChangeRecord index: $index, '
-      'removed: $removedCount, addedCount: $addedCount>';
-}
-
-/**
- * Synchronously deliver [Observable.changes] for all observables.
- * If new changes are added as a result of delivery, this will keep running
- * until all pending change records are delivered.
- */
-// TODO(jmesserly): this is a bit different from the ES Harmony version, which
-// allows delivery of changes to a particular observer:
-// http://wiki.ecmascript.org/doku.php?id=harmony:observe#object.deliverchangerecords
-// However the binding system needs delivery of everything, along the lines of:
-// https://github.com/toolkitchen/mdv/blob/stable/src/model.js#L19
-// https://github.com/rafaelw/ChangeSummary/blob/master/change_summary.js#L590
-// TODO(jmesserly): in the future, we can use this to trigger dirty checking.
-void deliverChangeRecords() {
-  if (_deliverCallbacks == null) return;
-
-  while (!_deliverCallbacks.isEmpty) {
-    var deliver = _deliverCallbacks.removeFirst();
-
-    try {
-      deliver();
-    } catch (e, s) {
-      // Schedule the error to be top-leveled later.
-      new Completer().completeError(e, s);
-    }
-  }
-
-  // Null it out, so [queueChangeRecords] will reschedule this method.
-  _deliverCallbacks = null;
-}
-
-/** Queues an action to happen during the [deliverChangeRecords] timeslice. */
-void queueChangeRecords(void deliverChanges()) {
-  if (_deliverCallbacks == null) {
-    _deliverCallbacks = new Queue<Function>();
-    runAsync(deliverChangeRecords);
-  }
-  _deliverCallbacks.add(deliverChanges);
-}
-
-Queue _deliverCallbacks;