HORIZON PROJECT

'use strict';

module.exports = balanced;

function balanced(a, b, str) {

  if (a instanceof RegExp) a = maybeMatch(a, str);

  if (b instanceof RegExp) b = maybeMatch(b, str);

  var r = range(a, b, str);

  return r && {

    start: r[0],

    end: r[1],

    pre: str.slice(0, r[0]),

    body: str.slice(r[0] + a.length, r[1]),

    post: str.slice(r[1] + b.length)

  };

}

function maybeMatch(reg, str) {

  var m = str.match(reg);

  return m ? m[0] : null;

}

balanced.range = range;

function range(a, b, str) {

  var begs, beg, left, right, result;

  var ai = str.indexOf(a);

  var bi = str.indexOf(b, ai + 1);

  var i = ai;

  if (ai >= 0 && bi > 0) {

    begs = [];

    left = str.length;

    while (i >= 0 && !result) {

      if (i == ai) {

        begs.push(i);

        ai = str.indexOf(a, i + 1);

      } else if (begs.length == 1) {

        result = [ begs.pop(), bi ];

      } else {

        beg = begs.pop();

        if (beg < left) {

          left = beg;

          right = bi;

        }

        bi = str.indexOf(b, i + 1);

      }

      i = ai < bi && ai >= 0 ? ai : bi;

    }

    if (begs.length) {

      result = [ left, right ];

    }

  }

  return result;

}