Factor a PhaseOutput class out of Phase.

pkg/barback/lib/src/asset_node.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.
 
 library barback.asset_node;
 
 import 'dart:async';
 
 import 'asset.dart';
 import 'asset_id.dart';
 import 'errors.dart';
 import 'transform_node.dart';
 
 /// Describes the current state of an asset as part of a transformation graph.
 ///
 /// An asset node can be in one of three states (see [AssetState]). It provides
 /// an [onStateChange] stream that emits an event whenever it changes state.
 ///
 /// Asset nodes are controlled using [AssetNodeController]s.
 class AssetNode {
   /// The id of the asset that this node represents.
   final AssetId id;
 
   /// The transform that created this asset node.
   ///
-  /// This is `null` for source assets.
-  final TransformNode transform;
+  /// This is `null` for source assets. It can change if the upstream transform
+  /// that created this asset changes; this change will *not* cause an
+  /// [onStateChange] event.
+  TransformNode get transform => _transform;
+  TransformNode _transform;
 
   /// The current state of the asset node.
   AssetState get state => _state;
   AssetState _state;
 
   /// The concrete asset that this node represents.
   ///
   /// This is null unless [state] is [AssetState.AVAILABLE].
   Asset get asset => _asset;
   Asset _asset;
@@ skipping 65 matching lines @@
 
   /// Returns a Future that completes as soon as the node is in a state that
   /// matches [test].
   ///
   /// The Future completes synchronously if this is already in such a state.
   Future<AssetState> _waitForState(bool test(AssetState state)) {
     if (test(state)) return new Future.sync(() => state);
     return onStateChange.firstWhere(test);
   }
 
-  AssetNode._(this.id, this.transform)
+  AssetNode._(this.id, this._transform)
       : _state = AssetState.DIRTY;
 
-  AssetNode._available(Asset asset, this.transform)
+  AssetNode._available(Asset asset, this._transform)
       : id = asset.id,
         _asset = asset,
         _state = AssetState.AVAILABLE;
 }
 
 /// The controller for an [AssetNode].
 ///
 /// This controls which state the node is in.
 class AssetNodeController {
   final AssetNode node;
 
   /// Creates a controller for a dirty node.
   AssetNodeController(AssetId id, [TransformNode transform])
       : node = new AssetNode._(id, transform);
 
   /// Creates a controller for an available node with the given concrete
   /// [asset].
   AssetNodeController.available(Asset asset, [TransformNode transform])
       : node = new AssetNode._available(asset, transform);
 
+  /// Creates a controller for a node whose initial state matches the current
+  /// state of [node].
+  AssetNodeController.from(AssetNode node)
+      : node = new AssetNode._(node.id, node.transform) {
+    if (node.state.isAvailable) {
+      setAvailable(node.asset);
+    } else if (node.state.isRemoved) {
+      setRemoved();
+    }
+  }
+
   /// Marks the node as [AssetState.DIRTY].
   void setDirty() {
     assert(node._state != AssetState.REMOVED);
     node._state = AssetState.DIRTY;
     node._asset = null;
     node._stateChangeController.add(AssetState.DIRTY);
   }
 
   /// Marks the node as [AssetState.REMOVED].
   ///
@@ skipping 11 matching lines @@
   /// It's an error to mark an already-available node as available. It should be
   /// marked as dirty first.
   void setAvailable(Asset asset) {
     assert(asset.id == node.id);
     assert(node._state != AssetState.REMOVED);
     assert(node._state != AssetState.AVAILABLE);
     node._state = AssetState.AVAILABLE;
     node._asset = asset;
     node._stateChangeController.add(AssetState.AVAILABLE);
   }
+
+  /// Sets the node's [AssetNode.transform] property.

[Bob Nystrom, 2013/08/21 21:23:40]

Add a bit explaining when/why this will occur.

[nweiz, 2013/08/22 18:30:49]

Done.

+  void setTransform(TransformNode transform) {
+    node._transform = transform;
+  }
 }
 
 // TODO(nweiz): add an error state.
 /// An enum of states that an [AssetNode] can be in.
 class AssetState {
   /// The node has a concrete asset loaded, available, and up-to-date. The asset
   /// is accessible via [AssetNode.asset]. An asset can only be marked available
   /// again from the [AssetState.DIRTY] state.
   static final AVAILABLE = const AssetState._("available");
 
@@ skipping 13 matching lines @@
 
   /// Whether this state is [AssetState.DIRTY].
   bool get isDirty => this == AssetState.DIRTY;
 
   final String name;
 
   const AssetState._(this.name);
 
   String toString() => name;
 }