packages/barback/test/transformer/check_content_and_rename.dart

// 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.test.transformer.check_content_and_rename;

import 'dart:async';

import 'package:barback/barback.dart';

import 'mock.dart';

/// A transformer that checks the extension and content of an asset, then
/// produces a new asset with a new extension and new content.
class CheckContentAndRenameTransformer extends MockTransformer {
  final String oldExtension;
  final String oldContent;
  final String newExtension;
  final String newContent;

  CheckContentAndRenameTransformer(
      {this.oldExtension,
      this.oldContent,
      this.newExtension,
      this.newContent}) {
    assert(oldExtension != null);
    assert(oldContent != null);
    assert(newExtension != null);
    assert(newContent != null);
  }

  bool doIsPrimary(AssetId id) => id.extension == '.$oldExtension';

  Future doApply(Transform transform) {
    return getPrimary(transform).then((input) {
      return input.readAsString().then((contents) {
        if (contents != oldContent) return;

        transform.addOutput(new Asset.fromString(
            input.id.changeExtension('.$newExtension'), newContent));
      });
    });
  }
}