First pass at build dependency graph for barback.

pkg/barback/lib/src/asset.dart

Index: pkg/barback/lib/src/asset.dart
diff --git a/pkg/barback/lib/src/asset.dart b/pkg/barback/lib/src/asset.dart
new file mode 100644
index 0000000000000000000000000000000000000000..924acfafed5d35a50f186fba31d2334405b32b85
--- /dev/null
+++ b/pkg/barback/lib/src/asset.dart
@@ -0,0 +1,97 @@
+// 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;
+
+import 'dart:async';
+import 'dart:io';
+
+/// A blob of content.
+///
+/// Assets may come from the file system, or as the output of a [Transformer].
+/// They are identified by [AssetId].
+abstract class Asset {
+  Asset();
+
+  factory Asset.fromFile(File file) {
+    return new _FileAsset(file);
+  }
+
+  factory Asset.fromString(String content) {
+    return new _StringAsset(content);
+  }
+
+  factory Asset.fromPath(String path) {
+    return new _FileAsset(new File(path));
+  }
+
+  // TODO(rnystrom): This prevents users from defining their own
+  // implementations of Asset. Use serialization package instead.
+  factory Asset.deserialize(data) {
+    // TODO(rnystrom): Handle errors.
+    switch (data[0]) {
+      case "file": return new _FileAsset(new File(data[1])); break;
+      case "string": return new _StringAsset(data[1]); break;
+    }
+  }
+
+  /// Returns the contents of the asset as a string.
+  // TODO(rnystrom): Figure out how binary assets should be handled.
+  String readAsString();
+
+  /// Streams the contents of the asset.
+  Stream<List<int>> read();
+
+  /// Serializes this [Asset] to an object that can be sent across isolates
+  /// and passed to [deserialize].
+  Object serialize();
+}
+
+/// An asset backed by a file on the local file system.
+class _FileAsset extends Asset {
+  final File _file;
+  _FileAsset(this._file);
+
+  String readAsString() => _file.readAsStringSync();
+  Stream<List<int>> read() => _file.openRead();
+
+  String toString() => 'File "${_file.path}"';
+
+  Object serialize() => ["file", _file.path];
+}
+
+/// An asset whose data is stored in a string.
+// TODO(rnystrom): Have something similar for in-memory binary assets.
+class _StringAsset extends Asset {
+  final String _contents;
+
+  _StringAsset(this._contents);
+
+  String readAsString() => _contents;
+
+  // TODO(rnystrom): Implement this and handle encoding.
+  Stream<List<int>> read() => throw new UnimplementedError();
+
+  String toString() {
+    // Don't show the whole string if it's long.
+    var contents = _contents;
+    if (contents.length > 40) {
+      contents = contents.substring(0, 20) + " ... " +
+                 contents.substring(contents.length - 20);
+    }
+
+    contents = _escape(contents);
+    return 'String "$contents"';
+  }
+
+  Object serialize() => ["string", _contents];
+
+  String _escape(String string) {
+    return string
+        .replaceAll("\"", r'\"')
+        .replaceAll("\n", r"\n")
+        .replaceAll("\r", r"\r")
+        .replaceAll("\t", r"\t");
+  }
+}