Start implementing pub object model. Rudimentary package cache class, and a simple pub command to l…

utils/pub/package.dart

+// Copyright (c) 2012, 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.
+
+/**
+ * A named, versioned, unit of code and resource reuse.
+ */
+class Package {
+  /**
+   * The name of the package.
+   */
+  final String name;
+
+  /**
+   * The names of the packages that this package depends on. This is what is
+   * specified in the pubspec when this package depends on another.
+   */
+  // TODO(rnystrom): When packages are versioned and sourced, this will likely
+  // be something more than just a string.
+  final Collection<String> dependencies;
+
+  /**
+   * The cache where this package is contained.
+   */
+  final PackageCache _cache;
+
+  /**
+   * Constructs a package. This should not be called directly. Instead, acquire
+   * packages from [PackageCache].
+   */
+  Package._(this._cache, this.name, this.dependencies);
+
+  /**
+   * Reads and returns all of the packages this package depends on.
+   */
+  Future<Collection<Package>> readDependencies() {
+    return Futures.wait(dependencies.map((name) => _cache.find(name)));
+  }
+}