negotiateLocale.js

/**
 * Translated from: https://github.com/mitsuhiko/babel/blob/e224a7b/babel/core.py
 * License: https://github.com/mitsuhiko/babel/blob/e224a7b/LICENSE
 */

var LOCALE_ALIASES = {
    'ar': 'ar_SY', 'bg': 'bg_BG', 'bs': 'bs_BA', 'ca': 'ca_ES', 'cs': 'cs_CZ',
    'da': 'da_DK', 'de': 'de_DE', 'el': 'el_GR', 'en': 'en_US', 'es': 'es_ES',
    'et': 'et_EE', 'fa': 'fa_IR', 'fi': 'fi_FI', 'fr': 'fr_FR', 'gl': 'gl_ES',
    'he': 'he_IL', 'hu': 'hu_HU', 'id': 'id_ID', 'is': 'is_IS', 'it': 'it_IT',
    'ja': 'ja_JP', 'km': 'km_KH', 'ko': 'ko_KR', 'lt': 'lt_LT', 'lv': 'lv_LV',
    'mk': 'mk_MK', 'nl': 'nl_NL', 'nn': 'nn_NO', 'no': 'nb_NO', 'pl': 'pl_PL',
    'pt': 'pt_PT', 'ro': 'ro_RO', 'ru': 'ru_RU', 'sk': 'sk_SK', 'sl': 'sl_SI',
    'sv': 'sv_SE', 'th': 'th_TH', 'tr': 'tr_TR', 'uk': 'uk_UA'
};

/**
 * Find the best match between available and requested locale strings.
 *
 * >>> negotiate_locale(['de_DE', 'en_US'], ['de_DE', 'de_AT'])
 * 'de_DE'
 * >>> negotiate_locale(['de_DE', 'en_US'], ['en', 'de'])
 * 'de'
 *
 * Case is ignored by the algorithm, the result uses the case of the preferred
 * locale identifier:
 *
 * >>> negotiate_locale(['de_DE', 'en_US'], ['de_de', 'de_at'])
 * 'de_DE'
 *
 * >>> negotiate_locale(['de_DE', 'en_US'], ['de_de', 'de_at'])
 * 'de_DE'
 *
 * By default, some web browsers unfortunately do not include the territory
 * in the locale identifier for many locales, and some don't even allow the
 * user to easily add the territory. So while you may prefer using qualified
 * locale identifiers in your web-application, they would not normally match
 * the language-only locale sent by such browsers. To workaround that, this
 * function uses a default mapping of commonly used langauge-only locale
 * identifiers to identifiers including the territory:
 *
 * >>> negotiate_locale(['ja', 'en_US'], ['ja_JP', 'en_US'])
 * 'ja_JP'
 *
 * Some browsers even use an incorrect or outdated language code, such as "no"
 * for Norwegian, where the correct locale identifier would actually be "nb_NO"
 * (Bokmål) or "nn_NO" (Nynorsk). The aliases are intended to take care of
 * such cases, too:
 *
 * >>> negotiate_locale(['no', 'sv'], ['nb_NO', 'sv_SE'])
 * 'nb_NO'
 *
 * You can override this default mapping by passing a different `aliases`
 * mapping to this function, or you can bypass the behavior althogher by
 * setting the `aliases` parameter to something falsey.
 *
 * :param preferred: the list of locale strings preferred by the user
 * :param available: the list of locale strings available
 * :param sep: character that separates the different parts of the locale
 *             strings
 * :param aliases: a mapping of aliases for locale identifiers
 */
function negotiate_locale(preferred, available, sep, aliases) {
  sep = sep || '_';
  aliases = aliases || LOCALE_ALIASES;
  var avail = [];
  for (var i=0, n=available.length; i<n; i++) {
    if (available[i]) {
      avail.push(angular.lowercase(available[i]));
    }
  }
  for (var i=0, n=preferred.length; i<n; i++) {
    var locale = preferred[i],
        ll = angular.lowercase(locale);
    if (avail.indexOf(ll) > -1) {
      return locale;
    }
    if (aliases) {
      if (ll in aliases) {
        var alias = aliases[ll].replace('_', sep);
        if (avail.indexOf(angular.lowercase(alias)) > -1) {
          return alias;
        }
      }
    }
    var parts = locale.split(sep);
    if (parts.length > 1 && avail.indexOf(angular.lowercase(parts[0])) > -1) {
      return parts[0];
    }
  }
}

Just noticed that 'ar' -> 'ar_AR' mapping looked funny to me and left a comment about it.