Expando Locale Example

expando_locale.dart

abstract class Locale {
  String get languageCode;
  String get scriptCode;
  String get regionCode;
  const factory Locale(String languageCode,
    [String regionOrScriptCode, String regionCode]) = _Locale._select;
}


class _Locale implements Locale {
  static Expando<_Locale> _normalized = Expando();
  final String _language;
  final String _region;
  final String _script;

  const _Locale._select(String language, [String regionOrScript, String region]) :
    this.validate(language,
         region == null ? null : regionOrScript,
         region == null ? regionOrScript : region);

  const _Locale.validate(this._language, this._script, this._region)
    : assert(_language != null),
      assert(_language.length >= 2),
      assert(_language.length <= 8),
      assert(_language.length != 4),
      assert((_script ?? "xxxx").length == 4),
      assert((_region ?? "xx").length >= 2),
      assert((_region ?? "xx").length <= 3);

  String get languageCode => _normal._language;
  String get scriptCode => _normal._script;
  String get regionCode => _normal._region;

  _Locale _normalize() {
    var language = _language.toLowerCase();
    var script = _script == null ? null : _capitalize(_script);
    var region = _region?.toUpperCase();
    // Add any other normalization desired here.
    if (identical(language, _language) &&
        identical(script, _script) &&
        identical(region, _region)) {
      return this;
    }
    return _Locale.validate(language, script, region);
  }

  _Locale get _normal => _normalized[this] ??= _normalize();

  Locale normalize() => _normal;

  int get hashCode => _normal.toString().hashCode;

  bool operator==(Object other) {
    if (other is Locale) {
      var normal = _normal;
      return normal._language == other.languageCode &&
        normal._script == other.scriptCode &&
        normal._region == other.regionCode;
    }
    return false;
  }

  String toString() {  
    var normal = _normal;
    var builder = new StringBuffer(normal._language);
    if (normal._script != null) {
      builder.write("_");
      builder.write(normal._script);
    }
    if (normal._region != null) {
      builder.write("_"); 
      builder.write(normal._region);
    }
    return builder.toString();
  }
}

String _capitalize(String word) {
  assert(word.length == 4);
  invalid: {
    if (word.codeUnitAt(0) & 0x20 != 0) break invalid;
    for (int i = 0; i < word.length; i++) {
      if (word.codeUnitAt(0) & 0x20 == 0) break invalid;
    }
    return word;
  }
  return word.substring(0, 1).toUpperCase() + word.substring(1).toLowerCase();
}


main() {
  print(const Locale("zh"));
  print(const Locale("zh", "TW"));
  var l1 = const Locale("zh", "Hant", "TW");
  var l2 = const Locale("ZH", "HANT", "tw");
  print(l1);
  print(l2);
  print(l1 == l2);
  print(l1.hashCode - l2.hashCode);
  try {
    Locale("zhzh");
  } catch (e) { 
    print(e); 
  }
}