// true  -> String#at
// false -> String#codePointAt
var $ = require('./$');
module.exports = function(TO_STRING){
  return function(that, pos){
    var s = String($.assertDefined(that))
      , i = $.toInteger(pos)
      , l = s.length
      , a, b;
    if(i < 0 || i >= l)return TO_STRING ? '' : undefined;
    a = s.charCodeAt(i);
    return a < 0xd800 || a > 0xdbff || i + 1 === l
      || (b = s.charCodeAt(i + 1)) < 0xdc00 || b > 0xdfff
        ? TO_STRING ? s.charAt(i) : a
        : TO_STRING ? s.slice(i, i + 2) : (a - 0xd800 << 10) + (b - 0xdc00) + 0x10000;
  };
};