/**
 * Parse "Range" header `str` relative to the given file `size`.
 *
 * @param {Number} size
 * @param {String} str
 * @return {Array}
 * @api public
 */

module.exports = function(size, str){
  var valid = true;
  var i = str.indexOf('=');

  if (-1 == i) return -2;

  var arr = str.slice(i + 1).split(',').map(function(range){
    var range = range.split('-')
      , start = parseInt(range[0], 10)
      , end = parseInt(range[1], 10);

    // -nnn
    if (isNaN(start)) {
      start = size - end;
      end = size - 1;
    // nnn-
    } else if (isNaN(end)) {
      end = size - 1;
    }

    // limit last-byte-pos to current length
    if (end > size - 1) end = size - 1;

    // invalid
    if (isNaN(start)
      || isNaN(end)
      || start > end
      || start < 0) valid = false;

    return {
      start: start,
      end: end
    };
  });

  arr.type = str.slice(0, i);

  return valid ? arr : -1;
};