export const SimpleReRE = /^\^\[((?:\\\[|\\\]|[^\[\]])+)\]([+*])\$$/;

export function isInvertable(re:string|RegExp) {

  let pattern = reSource(re);

  return SimpleReRE.test(pattern);
}

export function invertedRE(re:string|RegExp):string {

  let pattern = reSource(re);

  let simpleReMatch = SimpleReRE.exec(pattern);
  if (simpleReMatch) {
    let chars = simpleReMatch[1];
    if (chars.charAt(0) == '^') {
      chars = chars.substring(1);
    } else {
      chars = '^'+chars;
    }
    return `[${chars}]`;
  }

  return null;
}

function reSource(re: string|RegExp) {
  let pattern: string;
  switch (typeof re) {
    case 'string': pattern = re as string; break;
    case 'object': pattern = (re as RegExp).source; break;
    default: pattern = (null != re) ? (re as any).toString() : null; break
  }
  return pattern;
}