Make barback more package-aware.

pkg/barback/lib/src/asset_graph_manager.dart

Index: pkg/barback/lib/src/asset_graph_manager.dart
diff --git a/pkg/barback/lib/src/asset_graph_manager.dart b/pkg/barback/lib/src/asset_graph_manager.dart
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+++ b/pkg/barback/lib/src/asset_graph_manager.dart
@@ -0,0 +1,119 @@
+// 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_graph_manager;
+
+import 'dart:async';
+
+import 'package:stack_trace/stack_trace.dart';
+
+import 'asset.dart';
+import 'asset_provider.dart';
+import 'asset_graph.dart';
+import 'asset_id.dart';
+import 'errors.dart';
+import 'utils.dart';
+
+// TODO(nweiz): come up with better names for this and AssetGraph.

[Bob Nystrom, 2013/07/11 23:03:40]

Agreed. "Manager" is one of my biggest pet peeves.

How about "PackageGraph"?

[nweiz, 2013/07/15 22:11:44]

I like "PackageGraph", but where does that leave AssetGraph? I don't want to
just call it "Package", but it won't really encapsulate an asset graph once
transforms start reaching outside a given AssetGraph for cross-package assets.

[Bob Nystrom, 2013/07/16 17:36:01]

How about:

AssetGraphManager -> AssetGraph
AssetGraph -> PackageAssetGraph

?

[nweiz, 2013/07/16 19:39:39]

 2013/07/16 17:36:01, Bob Nystrom wrote:
I was thinking

AssetGraphManager -> PackageGraph
AssetGraph        -> AssetCascade

With "cascade" representing the way assets cascade through a series of phases.
This has the side benefit of having a different noun for the two classes, so a
variable named "_graph" consistently refers to a single type.

[Bob Nystrom, 2013/07/16 22:23:17]

SGTM.

+
+/// The asset manager for an entire application.
+///
+/// This tracks each package's [AssetGraph] and routes asset requests between
+/// them.
+class AssetGraphManager {
+  /// The provider that exposes asset and package information.
+  final AssetProvider provider;
+
+  /// The [AssetGraph] for each package.
+  final _graphs = <String, AssetGraph>{};
+
+  /// The current [BuildResult] for each package's [AssetGraph].

[Bob Nystrom, 2013/07/11 23:03:40]

"current" -> "last"

[nweiz, 2013/07/15 22:11:44]

I think "current" is slightly more accurate than "last". "last" implies that it
will exist until the next [BuildResult] exists, where in fact it will stop
existing once something changes in the [AssetGraph].

+  ///
+  /// The result for a given package will be `null` if that [AssetGraph] is
+  /// actively building.
+  final _graphResults = <String, BuildResult>{};
+
+  /// A stream that emits a [BuildResult] each time the build is completed,
+  /// whether or not it succeeded.
+  ///
+  /// This will emit a result only once every package's [AssetGraph] has
+  /// finished building.
+  ///
+  /// If an unexpected error in barback itself occurs, it will be emitted
+  /// through this stream's error channel.
+  Stream<BuildResult> get results => _resultsController.stream;
+  final _resultsController = new StreamController<BuildResult>.broadcast();
+
+  /// A stream that emits any errors from the asset graph or the transformers.
+  ///
+  /// This emits errors as they're detected. If an error occurs in one part of
+  /// the asset graph, unrelated parts will continue building.
+  ///
+  /// This will not emit programming errors from barback itself. Those will be
+  /// emitted through the [results] stream's error channel.
+  Stream get errors => _errors;
+  Stream _errors;
+
+  /// Creates a new [AssetGraphManager] that will transform assets in all
+  /// packages made available by [provider].
+  AssetGraphManager(this.provider) {
+    for (var package in provider.packages) {
+      var graph = new AssetGraph(
+          this, package, provider.getTransformers(package));

[Bob Nystrom, 2013/07/11 23:03:40]

Nit, but wrapping here looks weird to me. How about moving "this, package," to
the previous line?

[nweiz, 2013/07/15 22:11:44]

Done.

+      _graphResults[package] = new BuildResult.success();

[Bob Nystrom, 2013/07/11 23:03:40]

Why is this initially success and not null? Document.

[nweiz, 2013/07/15 22:11:44]

I wanted to make it consistent with the fact that the assets don't start
building until [updateSources] is called. At some point I'd like to add a more
principled way of kicking off a build, but for now I think keeping these
consistent makes sense.
Done.

+      _graphs[package] = graph;
+
+      graph.results.listen((result) {
+        _graphResults[graph.package] = result;
+        // If any graph hasn't yet finished, the overall build isn't finished
+        // either.
+        if (_graphResults.values.any((result) => result == null)) return;

[Bob Nystrom, 2013/07/11 23:03:40]

Having to walk this every time a package completes seems a bit gross. Here's a
thought:

Maybe AssetGraph should send an event when a build starts and then when it
completes. Then this class could keep a running tally of the ongoing builds.

[nweiz, 2013/07/15 22:11:44]

I don't think there are likely to be enough packages in the graph to make this
slow, especially since it's naturally limited by how often the user modifies
files. I don't think it's worth the complexity of adding a new event type to
[AssetGraph].

+
+        // Include all build errors for all graphs. If no graphs have errors,
+        // the result will automatically be considered a success.
+        _resultsController.add(new BuildResult(flatten(
+            _graphResults.values.map((result) => result.errors))));
+      }, onError: _resultsController.addError);
+    }
+
+    _errors = mergeStreams(_graphs.values.map((graph) => graph.errors));
+  }
+
+  /// Gets the asset identified by [id].
+  ///
+  /// If [id] is for a generated or transformed asset, this will wait until
+  /// it has been created and return it. If the asset cannot be found, throws
+  /// [AssetNotFoundException].
+  Future<Asset> getAssetById(AssetId id) {
+    var graph = _graphs[id.package];
+    if (graph != null) return graph.getAssetById(id);
+    return new Future.error(
+        new AssetNotFoundException(id),
+        new Trace.current().vmTrace);
+  }
+
+  /// Adds [sources] to the graph's known set of source assets.
+  ///
+  /// Begins applying any transforms that can consume any of the sources. If a
+  /// given source is already known, it is considered modified and all
+  /// transforms that use it will be re-applied.
+  void updateSources(Iterable<AssetId> sources) {
+    groupBy(sources, (id) => id.package).forEach((package, ids) {
+      var graph = _graphs[package];
+      if (graph == null) throw new ArgumentError("Unknown package $package.");
+      _graphResults[package] = null;
+      graph.updateSources(ids);
+    });
+  }
+
+  /// Removes [removed] from the graph's known set of source assets.
+  void removeSources(Iterable<AssetId> sources) {
+    groupBy(sources, (id) => id.package).forEach((package, ids) {
+      var graph = _graphs[package];
+      if (graph == null) throw new ArgumentError("Unknown package $package.");
+      _graphResults[package] = null;
+      graph.removeSources(ids);
+    });
+  }
+}