'use strict';
var $ = require('../internals/export');
var uncurryThis = require('../internals/function-uncurry-this');
var toIntegerOrInfinity = require('../internals/to-integer-or-infinity');
var thisNumberValue = require('../internals/this-number-value');
var $repeat = require('../internals/string-repeat');
var fails = require('../internals/fails');

var $RangeError = RangeError;
var $String = String;
var floor = Math.floor;
var repeat = uncurryThis($repeat);
var stringSlice = uncurryThis(''.slice);
var nativeToFixed = uncurryThis(1.0.toFixed);

var pow = function (x, n, acc) {
  return n === 0 ? acc : n % 2 === 1 ? pow(x, n - 1, acc * x) : pow(x * x, n / 2, acc);
};

var log = function (x) {
  var n = 0;
  var x2 = x;
  while (x2 >= 4096) {
    n += 12;
    x2 /= 4096;
  }
  while (x2 >= 2) {
    n += 1;
    x2 /= 2;
  } return n;
};

var multiply = function (data, n, c) {
  var index = -1;
  var c2 = c;
  while (++index < 6) {
    c2 += n * data[index];
    data[index] = c2 % 1e7;
    c2 = floor(c2 / 1e7);
  }
};

var divide = function (data, n) {
  var index = 6;
  var c = 0;
  while (--index >= 0) {
    c += data[index];
    data[index] = floor(c / n);
    c = (c % n) * 1e7;
  }
};

var dataToString = function (data) {
  var index = 6;
  var s = '';
  while (--index >= 0) {
    if (s !== '' || index === 0 || data[index] !== 0) {
      var t = $String(data[index]);
      s = s === '' ? t : s + repeat('0', 7 - t.length) + t;
    }
  } return s;
};

var FORCED = fails(function () {
  return nativeToFixed(0.00008, 3) !== '0.000' ||
    nativeToFixed(0.9, 0) !== '1' ||
    nativeToFixed(1.255, 2) !== '1.25' ||
    nativeToFixed(1000000000000000128.0, 0) !== '1000000000000000128';
}) || !fails(function () {
  // V8 ~ Android 4.3-
  nativeToFixed({});
});

// `Number.prototype.toFixed` method
// https://tc39.es/ecma262/#sec-number.prototype.tofixed
$({ target: 'Number', proto: true, forced: FORCED }, {
  toFixed: function toFixed(fractionDigits) {
    var number = thisNumberValue(this);
    var fractDigits = toIntegerOrInfinity(fractionDigits);
    var data = [0, 0, 0, 0, 0, 0];
    var sign = '';
    var result = '0';
    var e, z, j, k;

    // TODO: ES2018 increased the maximum number of fraction digits to 100, need to improve the implementation
    if (fractDigits < 0 || fractDigits > 20) throw new $RangeError('Incorrect fraction digits');
    // eslint-disable-next-line no-self-compare -- NaN check
    if (number !== number) return 'NaN';
    if (number <= -1e21 || number >= 1e21) return $String(number);
    if (number < 0) {
      sign = '-';
      number = -number;
    }
    if (number > 1e-21) {
      e = log(number * pow(2, 69, 1)) - 69;
      z = e < 0 ? number * pow(2, -e, 1) : number / pow(2, e, 1);
      z *= 0x10000000000000;
      e = 52 - e;
      if (e > 0) {
        multiply(data, 0, z);
        j = fractDigits;
        while (j >= 7) {
          multiply(data, 1e7, 0);
          j -= 7;
        }
        multiply(data, pow(10, j, 1), 0);
        j = e - 1;
        while (j >= 23) {
          divide(data, 1 << 23);
          j -= 23;
        }
        divide(data, 1 << j);
        multiply(data, 1, 1);
        divide(data, 2);
        result = dataToString(data);
      } else {
        multiply(data, 0, z);
        multiply(data, 1 << -e, 0);
        result = dataToString(data) + repeat('0', fractDigits);
      }
    }
    if (fractDigits > 0) {
      k = result.length;
      result = sign + (k <= fractDigits
        ? '0.' + repeat('0', fractDigits - k) + result
        : stringSlice(result, 0, k - fractDigits) + '.' + stringSlice(result, k - fractDigits));
    } else {
      result = sign + result;
    } return result;
  }
});