packages/barback/example/simple_transformer/lib/transformer.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.

import 'package:barback/barback.dart';

import 'dart:async';

class InsertCopyright extends Transformer {
  String copyright = "Copyright (c) 2014, the Example project authors.\n";

  // A constructor named "asPlugin" is required. It can be empty, but
  // it must be present. It is how pub determines that you want this
  // class to be publicly available as a loadable transformer plugin.
  InsertCopyright.asPlugin();

  Future<bool> isPrimary(AssetId id) async => id.extension == '.txt';

  Future apply(Transform transform) async {
    var content = await transform.primaryInput.readAsString();
    var id = transform.primaryInput.id;
    var newContent = copyright + content;
    transform.addOutput(new Asset.fromString(id, newContent));
  }
}