factor out enum indexing into reusable EnumIndex

packages/flutter_driver/lib/src/enum_util.dart

+// Copyright 2016 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+/// Indexes a list of `enum` values by simple name.
+///
+/// In Dart enum names are prefixed with enum class name. For example, for
+/// `enum Vote { yea, nay }`, `Vote.yea.toString()` produces `"Vote.yea"`
+/// rather than just `"yea"` - the simple name.
+///
+/// Example:
+///
+///     enum Vote { yea, nay }
+///     final index = new EnumIndex(Vote.values);
+///     index.lookupBySimpleName('yea');  // returns Vote.yea
+///     index.toSimpleName(Vote.nay); // returns 'nay'
+class EnumIndex<E> {
+  /// Creates an index of [enumValues].
+  EnumIndex(List<E> enumValues)
+    : _nameToValue = new Map<String, E>.fromIterable(
+        enumValues,
+        key: _getSimpleName
+      ),
+      _valueToName = new Map<E, String>.fromIterable(
+        enumValues,
+        value: _getSimpleName
+      );
+
+  final Map<String, E> _nameToValue;
+  final Map<E, String> _valueToName;
+
+  /// Given a [simpleName] finds the corresponding enum value.
+  E lookupBySimpleName(String simpleName) => _nameToValue[simpleName];
+
+  /// Returns the simple name for [enumValue].
+  String toSimpleName(E enumValue) => _valueToName[enumValue];
+}
+
+String _getSimpleName(dynamic enumValue) {
+  return enumValue.toString().split('.').last;
+}

packages/flutter_driver/lib/src/health.dart

@@ -2,6 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+import 'enum_util.dart';
 import 'message.dart';
 
 /// Requests an application health check.
@@ -22,6 +23,9 @@ enum HealthStatus {
   bad,
 }
 
+final EnumIndex<HealthStatus> _healthStatusIndex =
+    new EnumIndex<HealthStatus>(HealthStatus.values);
+
 /// Application health status.
 class Health extends Result {
   Health(this.status) {
@@ -29,26 +33,13 @@ class Health extends Result {
   }
 
   static Health fromJson(Map<String, dynamic> json) {
-    return new Health(_statusFromId(json['status']));
+    return new Health(_healthStatusIndex.lookupBySimpleName(json['status']));
   }
 
   /// Health status
   final HealthStatus status;
 
   Map<String, dynamic> toJson() => {
-    'status': _getStatusId(status)
+    'status': _healthStatusIndex.toSimpleName(status)
   };
 }
-
-String _getStatusId(HealthStatus status) => status.toString().split('.').last;
-
-final Map<String, HealthStatus> _idToStatus = new Map<String, HealthStatus>.fromIterable(
-  HealthStatus.values,
-  key: _getStatusId
-);
-
-HealthStatus _statusFromId(String id) {
-  return _idToStatus.containsKey(id)
-    ? _idToStatus[id]
-    : throw new ArgumentError.value(id, 'id', 'unknown');
-}