Parameterize uri resolution and parsing of options, use package:path

lib/output_config.dart

+// Copyright (c) 2014, 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.
+
+part of protoc;
+
+/// Configures where output of the protoc compiler should be placed and how to
+/// import one generated file from another.
+abstract class OutputConfiguration {
+
+  /// Returns [filePath] with it's extension replaced with '.pb.dart'.
+  String replacePathExtension(String filePath) =>
+      '${path.withoutExtension(filePath)}.pb.dart';
+
+  /// Returns [file] with it's extension replaced with '.pb.dart'.
+  Uri replaceUriExtension(Uri file) =>
+      path.url.toUri(replacePathExtension(path.url.fromUri(file)));
+
+  /// Resolves an import URI. Both [source] and [target] are .proto files,
+  /// where [target] is imported from [source]. The result URI can be used to
+  /// import [target]'s .pb.dart output from [source]'s .pb.dart output.
+  Uri resolveImport(Uri target, Uri source);
+
+  /// Returns the path, under the output folder, where the code will be
+  /// generated for [inputPath]. The input is expected to be a .proto file,
+  /// while the output is expected to be a .pb.dart file.
+  Uri outputPathFor(Uri inputPath);
+}
+
+/// Default [OutputConfiguration] that uses the same path as the input
+/// file for the output file (just replaces the extension), and that uses
+/// relative paths to resolve imports.
+class DefaultOutputConfiguration extends OutputConfiguration {
+
+  Uri outputPathFor(Uri input) => replaceUriExtension(input);
+
+  Uri resolveImport(Uri target, Uri source) {
+    var builder = path.url;
+    var targetPath = builder.fromUri(target);
+    var sourceDir = builder.dirname(builder.fromUri(source));
+    return builder.toUri(replacePathExtension(
+        builder.relative(targetPath, from: sourceDir)));
+  }
+}