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packages/barback/test/transformer/conditionally_consume_primary.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.
+
+library barback.test.transformer.conditionally_consume_primary;
+
+import 'dart:async';
+
+import 'package:barback/barback.dart';
+
+import 'rewrite.dart';
+
+/// A transformer that consumes its primary input only if its contents match a
+/// given pattern.
+class ConditionallyConsumePrimaryTransformer extends RewriteTransformer {
+  final Pattern content;
+
+  ConditionallyConsumePrimaryTransformer(String from, String to, this.content)
+      : super(from, to);
+
+  Future doApply(Transform transform) {
+    return getPrimary(transform).then((primary) {
+      return primary.readAsString().then((value) {
+        if (value.contains(content)) transform.consumePrimary();
+        return super.doApply(transform);
+      });
+    });
+  }
+}