Function splitLanguageTag

deps/v8/test/intl/assert.js:215–277

* Split a BCP 47 language tag into locale and extension.

(tag)

 * Split a BCP 47 language tag into locale and extension.
 */
function splitLanguageTag(tag) {
  // Search for the beginning of one or more extension tags, each of which
  // contains a singleton tag followed by one or more subtags. The equivalent
  // regexp is: /(-[0-9A-Za-z](-[0-9A-Za-z]{2,8})+)+$/. For example, in
  // 'de-DE-u-co-phonebk' the matched extension tags are '-u-co-phonebk'.
  //
  // The below is a mini-parser that reads backwards from the end of the string.

  function charCode(char) { return char.charCodeAt(0); }
  function isAlphaNumeric(code) {
    return (charCode("0") <= code && code <= charCode("9")) ||
           (charCode("A") <= code && code <= charCode("Z")) ||
           (charCode("a") <= code && code <= charCode("z"));
  }

  const MATCH_SUBTAG = 0;
  const MATCH_SINGLETON_OR_SUBTAG = 1;
  let state = MATCH_SUBTAG;

  const MINIMUM_TAG_LENGTH = 2;
  const MAXIMUM_TAG_LENGTH = 8;
  let currentTagLength = 0;

  // -1 signifies failure, a non-negative integer is the start index of the
  // extension tag.
  let extensionTagStartIndex = -1;

  for (let i = tag.length - 1; i >= 0; i--) {
    const currentCharCode = tag.charCodeAt(i);
    if (currentCharCode == charCode("-")) {
      if (state == MATCH_SINGLETON_OR_SUBTAG && currentTagLength == 1) {
        // Found the singleton tag, the match succeeded.
        // Save the matched index, and reset the state. After this point, we
        // definitely have a match, but we may still find another extension tag
        // sequence.
        extensionTagStartIndex = i;
        state = MATCH_SUBTAG;
        currentTagLength = 0;
      } else if (MINIMUM_TAG_LENGTH <= currentTagLength &&
                currentTagLength <= MAXIMUM_TAG_LENGTH) {
        // Found a valid subtag.
        state = MATCH_SINGLETON_OR_SUBTAG;
        currentTagLength = 0;
      } else {
        // Invalid subtag (too short or too long).
        break;
      }
    } else if (isAlphaNumeric(currentCharCode)) {
      // An alphanumeric character is potentially part of a tag.
      currentTagLength++;
    } else {
      // Any other character is invalid.
      break;
    }
  }

  if (extensionTagStartIndex != -1) {
    return { locale: tag.substring(0, extensionTagStartIndex),