Added .packages, packages/ discovery.

lib/src/packages_impl.dart

+// Copyright (c) 2015, 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 package_config.packages_impl;
+
+import "dart:collection" show UnmodifiableMapView;
+import "dart:io" show Directory;
+import "package:path/path.dart" as path;
+import "../packages.dart";
+import "util.dart" show checkValidPackageUri;
+
+/// A [Packages] null-object.
+class NoPackages implements Packages {
+  const NoPackages();
+
+  Uri resolve(Uri packageUri, {Uri notFound(Uri packageUri)}) {
+    String packageName = checkValidPackageUri(packageUri);
+    if (notFound != null) return notFound(packageUri);
+    throw new ArgumentError.value(packageUri, "packageUri",
+                                  'No package named "$packageName"');
+  }
+
+  Iterable<String> get packages => new Iterable<String>.empty();
+
+  Map<String, Uri> asMap() => const<String,Uri>{};
+}
+
+
+/// Base class for [Packages] implementations.
+///
+/// This class implements the [resolve] method in terms of a private
+/// member
+abstract class _PackagesBase implements Packages {
+  Uri resolve(Uri packageUri, {Uri notFound(Uri packageUri)}) {
+    packageUri = packageUri.normalizePath();
+    String packageName = checkValidPackageUri(packageUri);
+    Uri packageBase = _getBase(packageName);
+    if (packageBase == null) {
+      if (notFound != null) return notFound(packageUri);
+      throw new ArgumentError.value(packageUri, "packageUri",
+                                    'No package named "$packageName"');
+    }
+    String packagePath = packageUri.path.substring(packageName.length + 1);
+    return packageBase.resolve(packagePath);
+  }
+
+  /// Find a base location for a package name.
+  ///
+  /// Returns `null` if no package exists with that name, and that can be
+  /// determined.
+  Uri _getBase(String packageName);
+}
+
+/// A [Packages] implementation based on an existing map.
+class MapPackages extends _PackagesBase {
+  final Map<String, Uri> _mapping;
+  MapPackages(this._mapping);
+
+  Uri _getBase(String packageName) => _mapping[packageName];
+
+  Iterable<String> get packages => _mapping.keys;
+
+  Map<String, Uri> asMap() => new UnmodifiableMapView<String, Uri>(_mapping);
+}
+
+/// A [Packages] implementation based on a local directory.
+class FilePackagesDirectoryPackages extends _PackagesBase {
+  final Directory _packageDir;
+  FilePackagesDirectoryPackages(this._packageDir);
+
+  Uri _getBase(String packageName) =>
+      new Uri.directory(path.join(packageName,''));
+
+  Iterable<String> _listPackageNames() {
+    return _packageDir.listSync()
+                      .where((e) => e is Directory)
+                      .map((e) => path.basename(e.path));
+  }
+
+  Iterable<String> get packages {
+    return _listPackageNames();
+  }
+
+  Map<String, Uri> asMap() {
+    var result = <String, Uri>{};
+    for (var packageName in _listPackageNames()) {
+      result[packageName] = _getBase(packageName);
+    }
+    return new UnmodifiableMapView<String, Uri>(result);
+  }
+}
+
+/// A [Packages] implementation based on a remote (e.g., HTTP) directory.
+///
+/// There is no way to detect which packages exist short of trying to use
+/// them. You can't necessarily check whether a directory exists,
+/// except by checking for a know file in the directory.
+class NonFilePackagesDirectoryPackages extends _PackagesBase {
+  final Uri _packageBase;
+  NonFilePackagesDirectoryPackages(this._packageBase);
+
+  Uri _getBase(String packageName) => _packageBase.resolve("$packageName/");
+
+  Error _failListingPackages() {
+    return new UnsupportedError(
+        "Cannot list packages for a ${_packageBase.scheme}: "
+        "based package root");
+  }
+
+  Iterable<String> get packages {
+    throw _failListingPackages();
+  }
+
+  Map<String, Uri> asMap() {
+    throw _failListingPackages();
+  }
+}