Add async initialization for Intl.message and an example

pkg/intl/message_lookup_local.dart

Index: pkg/intl/message_lookup_local.dart
===================================================================
--- pkg/intl/message_lookup_local.dart	(revision 12066)
+++ pkg/intl/message_lookup_local.dart	(working copy)
@@ -3,7 +3,11 @@
 // BSD-style license that can be found in the LICENSE file.
 
 /**
- * Message/plural format library with locale support.
+ * Message/plural format library with locale support. This can have different
+ * implementations based on the mechanism for finding the localized versions
+ * of messages. This version expects them to be in a library named e.g.
+ * 'messages_en_US'. The prefix is set in the [initializeMessages] call, which
+ * must be made for a locale before any lookups can be done.
  *
  *
  * _message example:
@@ -34,43 +38,93 @@
  */
  //TODO(efortuna): documentation example involving the offset parameter?
 
-class IntlMessage {
+#library('message_lookup_local');
 
-  /** String describing the use case for this message. */
-  String _messageDescription;
+#import('intl.dart');
+#import('dart:mirrors');
 
-  /**
-   * String that contains the message to be displayed. It may contain
-   * placeholders in the form of string interpolated items (ie 'hello$foo') that
-   * will be substituted in to complete the message.
-   * See tests/message_format_test.dart for more examples.
+/**
+ * Initialize the user messages for [localeName]. Note that this is an ASYNC
+ * operation. This must be called before attempting to use messages in
+ * [localeName].
+ */
+Future initializeMessages(localeName, [String source = 'messages_']) {
+  initializeInternalMessageLookup(
+      () => new MessageLookupLocal(localeName, source));
+  _initializeMessagesForLocale(localeName);
+  return new Future.immediate(null);
+}
+
+void _initializeMessagesForLocale(String localeName) {}
+
+class MessageLookupLocal {
+  /** Prevent infinite recursion when looking up the message. */
+  bool _lookupInProgress = false;
+
+  /** The libraries we can look in for internationalization messages. */
+  Map<String, LibraryMirror> _libraries;
+
+  /** The prefix used to find libraries that contain localized messages.
+   * So, if this is 'messages_' we would look for messages for the locale
+   * 'pt_BR' in a library named 'messages_pt_BR'.
    */
-  String _message;
+  String _sourcePrefix;
 
   /**
-   * String indicating the locale code with which the message is to be
-   * formatted (such as en-CA).
+   * Constructor. The [localeName] is of the form 'en' or 'en_US'.
+   *The [source] parameter defines the prefix that is used to find
+   * libraries that contain localized messages. So with the default value of
+   * 'messages_', we would look for messages for the locale 'pt_BR' in a library
+   * named 'messages_pt_BR'.
    */
-  String _languageCode;
+  MessageLookupLocal(String localeName, this._sourcePrefix) {
+    _libraries = currentMirrorSystem().libraries;
+  }
 
-  /** Examples of the placeholders used in the message string. */
-  Map _messageExamples;
-
   /**
-   * Accepts a String [_message] that contains the message (that
-   * will be internationalized). A String [_messageDescription] describes the
-   * use case for this string in the program, and [examples] provides a map of
-   * examples for the items (if any) to be subsituted into [_message].
-   * It also optionally accepts a [_languageCode] to specify the particular
-   * language to return content in (necessary if the Dart code is not running in
-   * a browser). The values of [desc] and [examples] *must* be
-   * simple Strings available at compile time: no String interpolation or
-   * concatenation.
+   * Return the localized version of a message. We are passed the original
+   * version of the message, which consists of a
+   * [message_str] that will be translated, and which may be interpolated
+   * based on one or more variables, a [desc] providing a description of usage
+   * for the [message_str], and a map of [examples] for each data element to be
+   * substituted into the message.
+   *
+   * For example, if message="Hello, $name", then
+   * examples = {'name': 'Sparky'}. If not using the user's default locale, or
+   * if the locale is not easily detectable, explicitly pass [locale].
+   *
+   * The values of [desc] and [examples] are not used at run-time but are only
+   * made available to the translators, so they MUST be simple Strings available
+   * at compile time: no String interpolation or concatenation.
+   * The expected usage of this is inside a function that takes as parameters
+   * the variables used in the interpolated string.
+   *
+   * Ultimately, the information about the enclosing function and its arguments
+   * will be extracted automatically but for the time being it must be passed
+   * explicitly in the [name] and [args] arguments.
    */
-  IntlMessage(this._message, [final String desc='', final Map examples=const {},
-              final String locale='']) {
-    this._messageDescription = desc;
-    this._messageExamples = examples;
-    this._languageCode = locale;
+  String lookupMessage(String message_str, [final String desc='',
+      final Map examples=const {}, String locale,
+      String name, List<String> args]) {
+    if (name == null) return message_str;
+    // The translations also make use of Intl.message, so we need to not
+    // recurse and just stop when we find the first substitution.
+    if (_lookupInProgress) return message_str;
+    _lookupInProgress = true;
+    var result;
+    try {
+      // TODO(alanknight): Look up alternate forms, e.g. en for en_US
+      var actualLocale = (locale == null) ? Intl.getCurrentLocale() : locale;
+      LibraryMirror messagesForThisLocale =
+          _libraries['$_sourcePrefix$actualLocale'];
+      if (messagesForThisLocale == null) return message_str;
+      MethodMirror localized = messagesForThisLocale.functions[name];
+      if (localized == null) return message_str;
+      result = messagesForThisLocale.invoke(localized.simpleName, args);
+      }
+    finally {
+      _lookupInProgress = false;
+    }
+    return result.value.reflectee;
   }
-}
+}