Queue _extractParts()

in lib/message_format.dart [464:512]
41 lines of code
7 McCabe index (conditional complexity)

  Queue<_ElementTypeAndVal> _extractParts(String pattern) {
    var prevPos = 0;
    var braceStack = Queue<String>();
    var results = Queue<_ElementTypeAndVal>();

    var braces = RegExp('[{}]');

    Match match;
    for (match in braces.allMatches(pattern)) {
      var pos = match.start;
      if (match[0] == '}') {
        String? brace;
        try {
          brace = braceStack.removeLast();
        } on StateError {
          _checkAndThrow(brace != '}', 'No matching } for {.');
        }
        _checkAndThrow(brace == '{', 'No matching { for }.');

        if (braceStack.isEmpty) {
          // End of the block.
          var part = _ElementTypeAndVal(
              _ElementType.block, pattern.substring(prevPos, pos));
          results.add(part);
          prevPos = pos + 1;
        }
      } else {
        if (braceStack.isEmpty) {
          var substring = pattern.substring(prevPos, pos);
          if (substring != '') {
            results.add(_ElementTypeAndVal(_ElementType.string, substring));
          }
          prevPos = pos + 1;
        }
        braceStack.add('{');
      }
    }

    // Take care of the final string, and check if the braceStack is empty.
    _checkAndThrow(
        braceStack.isEmpty, 'There are mismatched { or } in the pattern.');

    var substring = pattern.substring(prevPos);
    if (substring != '') {
      results.add(_ElementTypeAndVal(_ElementType.string, substring));
    }

    return results;
  }