Add support for transformer clusters to barback.

pkg/barback/lib/src/phase.dart

Index: pkg/barback/lib/src/phase.dart
diff --git a/pkg/barback/lib/src/phase.dart b/pkg/barback/lib/src/phase.dart
index 1230bea094e36970d402547ec6b386c868c33ec0..b83061bb96a1a200fd730319aef32d4c70375978 100644
--- a/pkg/barback/lib/src/phase.dart
+++ b/pkg/barback/lib/src/phase.dart
@@ -11,11 +11,14 @@ import 'asset_cascade.dart';
 import 'asset_id.dart';
 import 'asset_node.dart';
 import 'asset_set.dart';
+import 'group_runner.dart';
 import 'errors.dart';
+import 'phase_forwarder.dart';
 import 'phase_input.dart';
 import 'phase_output.dart';
 import 'stream_pool.dart';
 import 'transformer.dart';
+import 'transformer_group.dart';
 import 'utils.dart';
 
 /// One phase in the ordered series of transformations in an [AssetCascade].
@@ -39,15 +42,38 @@ class Phase {
   /// Their outputs will be available to the next phase.
   final Set<Transformer> _transformers;
 
+  /// The groups for this phase.
+  final _groups = new Map<TransformerGroup, GroupRunner>();
+
   /// The inputs for this phase.
   ///
   /// For the first phase, these will be the source assets. For all other
   /// phases, they will be the outputs from the previous phase.
   final _inputs = new Map<AssetId, PhaseInput>();
 
+  /// The forwarders for this phase.
+  final _forwarders = new Map<AssetId, PhaseForwarder>();
+
   /// The outputs for this phase.
   final _outputs = new Map<AssetId, PhaseOutput>();
 
+  // TODO(nweiz): Don't re-calculate this on the fly all the time.
+  /// The set of all [AssetNode.origin] properties of the input assets for this
+  /// phase.
+  ///
+  /// This is used to determine which assets have been passed unmodified through
+  /// [_inputs] or [_groups]. Each input asset has a PhaseInput in [_inputs]. If
+  /// that input isn't consumed by any transformers, it will be forwarded
+  /// through the PhaseInput. However, it's possible that it was consumed by a
+  /// group, and so shouldn't be forwarded through the phase as a whole.
+  ///
+  /// In order to detect whether an output has been forwarded through a group or
+  /// a PhaseInput, we must be able to distinguish it from other outputs with
+  /// the same id. To do so, we check if its origin is in [_inputOrigins]. If
+  /// so, it's been forwarded unmodified.
+  Set<AssetNode> get _inputOrigins =>
+    _inputs.values.map((input) => input.input.origin).toSet();
+
   /// A stream that emits an event whenever this phase becomes dirty and needs
   /// to be run.
   ///
@@ -62,6 +88,10 @@ class Phase {
   /// This is used whenever an input is added or transforms are changed.
   final _onDirtyController = new StreamController.broadcast(sync: true);
 
+  /// Whether this phase is dirty and needs to be run.
+  bool get isDirty => _inputs.values.any((input) => input.isDirty) ||
+      _groups.values.any((group) => group.isDirty);
+
   /// The phase after this one.
   ///
   /// Outputs from this phase will be passed to it.
@@ -69,16 +99,24 @@ class Phase {
   Phase _next;
 
   /// Returns all currently-available output assets for this phase.
-  AssetSet get availableOutputs {
-    return new AssetSet.from(_outputs.values
+  Set<AssetNode> get availableOutputs {
+    return _outputs.values
         .map((output) => output.output)
         .where((node) => node.state.isAvailable)
-        .map((node) => node.asset));
+        .toSet();
   }
 
-  Phase(this.cascade, Iterable<Transformer> transformers)
-      : _transformers = transformers.toSet() {
+  // TODO(nweiz): Rather than passing the cascade and the phase everywhere,
+  // create an interface that just exposes [getInput]. Emit errors via
+  // [AssetNode]s.
+  Phase(this.cascade, Iterable transformers)
+      : _transformers = transformers.where((op) => op is Transformer).toSet() {
     _onDirtyPool.add(_onDirtyController.stream);
+
+    for (var group in transformers.where((op) => op is TransformerGroup)) {
+      _groups[group] = new GroupRunner(cascade, group);
+      _onDirtyPool.add(_groups[group].onDirty);
+    }
   }
 
   /// Adds a new asset as an input for this phase.
@@ -94,11 +132,29 @@ class Phase {
   void addInput(AssetNode node) {
     if (_inputs.containsKey(node.id)) _inputs[node.id].remove();
 
+    // Each group is one channel along which an asset may be forwarded. Then
+    // there's one additional channel for the non-grouped transformers.
+    var forwarder = new PhaseForwarder(_groups.length + 1);
+    _forwarders[node.id] = forwarder;
+    forwarder.onForwarding.listen((asset) {
+      _addOutput(asset);
+
+      var exception = _outputs[asset.id].collisionException;
+      if (exception != null) cascade.reportError(exception);
+    });
+
     var input = new PhaseInput(this, node, _transformers);
     _inputs[node.id] = input;
-    input.input.whenRemoved.then((_) => _inputs.remove(node.id));
+    input.input.whenRemoved.then((_) {
+      _inputs.remove(node.id);
+      _forwarders.remove(node.id).remove();
+    });
     _onDirtyPool.add(input.onDirty);
     _onDirtyController.add(null);
+
+    for (var group in _groups.values) {
+      group.addInput(node);
+    }
   }
 
   /// Gets the asset node for an input [id].
@@ -124,19 +180,41 @@ class Phase {
   }
 
   /// Set this phase's transformers to [transformers].
-  void updateTransformers(Iterable<Transformer> transformers) {
+  void updateTransformers(Iterable transformers) {
     _onDirtyController.add(null);
+
+    var actualTransformers = transformers.where((op) => op is Transformer);
     _transformers.clear();
-    _transformers.addAll(transformers);
+    _transformers.addAll(actualTransformers);
     for (var input in _inputs.values) {
-      input.updateTransformers(_transformers);
+      input.updateTransformers(actualTransformers);
+    }
+
+    var newGroups = transformers.where((op) => op is TransformerGroup)
+        .toSet();
+    var oldGroups = _groups.keys.toSet();
+    for (var removed in oldGroups.difference(newGroups)) {
+      _groups.remove(removed).remove();
+    }
+
+    for (var added in newGroups.difference(oldGroups)) {
+      var runner = new GroupRunner(cascade, added);
+      _groups[added] = runner;
+      _onDirtyPool.add(runner.onDirty);
+      for (var input in _inputs.values) {
+        runner.addInput(input.input);
+      }
+    }
+
+    for (var forwarder in _forwarders.values) {
+      forwarder.numChannels = _groups.length + 1;
     }
   }
 
   /// Add a new phase after this one with [transformers].
   ///
   /// This may only be called on a phase with no phase following it.
-  Phase addPhase(Iterable<Transformer> transformers) {
+  Phase addPhase(Iterable transformers) {
     assert(_next == null);
     _next = new Phase(cascade, transformers);
     for (var output in _outputs.values.toList()) {
@@ -162,6 +240,9 @@ class Phase {
     for (var input in _inputs.values.toList()) {
       input.remove();
     }
+    for (var group in _groups.values) {
+      group.remove();
+    }
     _onDirtyPool.close();
   }
 
@@ -177,26 +258,34 @@ class Phase {
   /// Returns a future that completes when processing is done. If there is
   /// nothing to process, returns `null`.
   Future process() {
-    if (!_inputs.values.any((input) => input.isDirty)) return null;
+    if (!isDirty) return null;
 
     var outputIds = new Set<AssetId>();
-    return Future.wait(_inputs.values.map((input) {
-      if (!input.isDirty) return new Future.value(new Set());
-      return input.process().then((outputs) {
-        for (var asset in outputs) {
-          outputIds.add(asset.id);
-          if (_outputs.containsKey(asset.id)) {
-            _outputs[asset.id].add(asset);
-          } else {
-            _outputs[asset.id] = new PhaseOutput(this, asset);
-            _outputs[asset.id].output.whenRemoved.then((_) {
-              _outputs.remove(asset.id);
-            });
-            if (_next != null) _next.addInput(_outputs[asset.id].output);
-          }
+    void _handleOutputs(Set<AssetNode> outputs) {
+      for (var asset in outputs) {
+        if (_inputOrigins.contains(asset.origin)) {
+          _forwarders[asset.id].addIntermediateAsset(asset);
+          continue;
         }
-      });
-    })).then((_) {
+
+        outputIds.add(asset.id);
+        _addOutput(asset);
+      }
+    }
+
+    var outputFutures = [];
+    outputFutures.addAll(_inputs.values.map((input) {
+      if (!input.isDirty) return new Future.value(new Set());
+      return input.process().then(_handleOutputs);
+    }));
+    outputFutures.addAll(_groups.values.map((input) {
+      if (!input.isDirty) return new Future.value(new Set());
+      return input.process().then(_handleOutputs);
+    }));
+
+    // TODO(nweiz): handle pass-through.
+
+    return Future.wait(outputFutures).then((_) {
       // Report collisions in a deterministic order.
       outputIds = outputIds.toList();
       outputIds.sort((a, b) => a.compareTo(b));
@@ -209,4 +298,17 @@ class Phase {
       }
     });
   }
+
+  /// Add [asset] as an output of this phase.
+  void _addOutput(AssetNode asset) {
+    if (_outputs.containsKey(asset.id)) {
+      _outputs[asset.id].add(asset);
+    } else {
+      _outputs[asset.id] = new PhaseOutput(this, asset);
+      _outputs[asset.id].output.whenRemoved.then((_) {
+        _outputs.remove(asset.id);
+      });
+      if (_next != null) _next.addInput(_outputs[asset.id].output);
+    }
+  }
 }