Reorganize barback's source files.

pkg/barback/lib/src/node_status.dart

-// Copyright (c) 2014, 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.node_status;
-
-/// The status of a node in barback's package graph.
-///
-/// A node has three possible statuses: [IDLE], [MATERIALIZING], and [RUNNING].
-/// These are ordered from least dirty to most dirty; the [dirtier] and
-/// [dirtiest] functions make use of this ordering.
-class NodeStatus {
-  /// The node has finished its work and won't do anything else until external
-  /// input causes it to.
-  ///
-  /// For deferred nodes, this may indicate that they're finished declaring
-  /// their outputs and waiting to be forced.
-  static const IDLE = const NodeStatus("idle");
-
-  /// The node has declared its outputs but their concrete values are still
-  /// being generated.
-  ///
-  /// This is only meaningful for nodes that are or contain declaring
-  /// transformers. Note that a lazy transformer that's declared its outputs but
-  /// isn't actively working to generate them is considered [IDLE], not
-  /// [MATERIALIZING].
-  static const MATERIALIZING = const NodeStatus("materializing");
-
-  /// The node is actively working on declaring or generating its outputs.
-  ///
-  /// Declaring transformers are only considered dirty until they're finished
-  /// declaring their outputs; past that point, they're always either
-  /// [MATERIALIZING] or [IDLE]. Non-declaring transformers, by contrast, are
-  /// always either [RUNNING] or [IDLE].
-  static const RUNNING = const NodeStatus("running");
-
-  final String _name;
-
-  /// Returns the dirtiest status in [statuses].
-  static NodeStatus dirtiest(Iterable<NodeStatus> statuses) =>
-      statuses.fold(NodeStatus.IDLE,
-          (status1, status2) => status1.dirtier(status2));
-
-  const NodeStatus(this._name);
-
-  String toString() => _name;
-
-  /// Returns [this] or [other], whichever is dirtier.
-  NodeStatus dirtier(NodeStatus other) {
-    if (this == RUNNING || other == RUNNING) return RUNNING;
-    if (this == MATERIALIZING || other == MATERIALIZING) return MATERIALIZING;
-    return IDLE;
-  }
-}