lib/message_lookup_by_library.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.

/// 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.
///
/// See Intl class comment or `tests/message_format_test.dart` for more
/// examples.
library message_lookup_by_library;

import 'package:intl/intl.dart';
import 'package:intl/src/intl_helpers.dart';

/// This is a message lookup mechanism that delegates to one of a collection
/// of individual [MessageLookupByLibrary] instances.
class CompositeMessageLookup implements MessageLookup {
  /// A map from locale names to the corresponding lookups.
  Map<String, MessageLookupByLibrary> availableMessages = {};

  /// Return true if we have a message lookup for [localeName].
  bool localeExists(String localeName) =>
      availableMessages.containsKey(localeName);

  /// The last locale in which we looked up messages.
  ///
  ///  If this locale matches the new one then we can skip looking up the
  ///  messages and assume they will be the same as last time.
  String? _lastLocale;

  /// Caches the last messages that we found
  MessageLookupByLibrary? _lastLookup;

  /// Look up the message with the given [name] and [locale] and return the
  /// translated version with the values in [args] interpolated.  If nothing is
  /// found, return the result of [ifAbsent] or [messageText].
  @override
  String? lookupMessage(String? messageText, String? locale, String? name,
      List<Object>? args, String? meaning,
      {MessageIfAbsent? ifAbsent}) {
    // If passed null, use the default.
    var knownLocale = locale ?? Intl.getCurrentLocale();
    var messages = (knownLocale == _lastLocale)
        ? _lastLookup
        : _lookupMessageCatalog(knownLocale);
    // If we didn't find any messages for this locale, use the original string,
    // faking interpolations if necessary.
    if (messages == null) {
      return ifAbsent == null ? messageText : ifAbsent(messageText, args);
    }
    return messages.lookupMessage(messageText, locale, name, args, meaning,
        ifAbsent: ifAbsent);
  }

  /// Find the right message lookup for [locale].
  MessageLookupByLibrary? _lookupMessageCatalog(String locale) {
    var verifiedLocale = Intl.verifiedLocale(locale, localeExists,
        onFailure: (locale) => locale);
    _lastLocale = locale;
    _lastLookup = availableMessages[verifiedLocale];
    return _lastLookup;
  }

  /// If we do not already have a locale for [localeName] then
  /// [findLocale] will be called and the result stored as the lookup
  /// mechanism for that locale.
  @override
  void addLocale(String localeName, Function findLocale) {
    if (localeExists(localeName)) return;
    var canonical = Intl.canonicalizedLocale(localeName);
    var newLocale = findLocale(canonical);
    if (newLocale != null) {
      availableMessages[localeName] = newLocale;
      availableMessages[canonical] = newLocale;
      // If there was already a failed lookup for [newLocale], null the cache.
      if (_lastLocale == newLocale) {
        _lastLocale = null;
        _lastLookup = null;
      }
    }
  }
}

/// This provides an abstract class for messages looked up in generated code.
/// Each locale will have a separate subclass of this class with its set of
/// messages. See generate_localized.dart.
abstract class MessageLookupByLibrary {
  /// Return the localized version of a message. We are passed the original
  /// version of the message, which consists of a
  /// [messageText] that will be translated, and which may be interpolated
  /// based on one or more variables.
  ///
  /// 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].
  ///
  /// 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.
  String? lookupMessage(String? messageText, String? locale, String? name,
      List<Object>? args, String? meaning,
      {MessageIfAbsent? ifAbsent}) {
    var actualName = computeMessageName(name, messageText, meaning);
    Object? translation;
    if (actualName != null) {
      translation = this[actualName];
    }
    if (translation == null) {
      return ifAbsent == null ? messageText : ifAbsent(messageText, args);
    } else {
      args = args ?? const [];
      return evaluateMessage(translation, args);
    }
  }

  /// Evaluate the translated message and return the translated string.
  String? evaluateMessage(translation, List<dynamic> args) {
    return Function.apply(translation, args);
  }

  /// Return our message with the given name
  dynamic operator [](String messageName) => messages[messageName];

  /// Subclasses should override this to return a list of their message
  /// implementations. In this class these are functions, but subclasses may
  /// implement them differently.
  Map<String, dynamic> get messages;

  /// Subclasses should override this to return their locale, e.g. 'en_US'
  String get localeName;

  @override
  String toString() => localeName;

  /// Return a function that returns the given string.
  /// An optimization for dart2js, used from the generated code.
  static String Function() simpleMessage(translatedString) =>
      () => translatedString;
}