'use strict';
var numberIsNan = require('number-is-nan');

module.exports = function (num) {
	if (typeof num !== 'number' || numberIsNan(num)) {
		throw new TypeError('Expected a number, got ' + typeof num);
	}

	var exponent;
	var unit;
	var neg = num < 0;
	var units = ['B', 'kB', 'MB', 'GB', 'TB', 'PB', 'EB', 'ZB', 'YB'];

	if (neg) {
		num = -num;
	}

	if (num < 1) {
		return (neg ? '-' : '') + num + ' B';
	}

	exponent = Math.min(Math.floor(Math.log(num) / Math.log(1000)), units.length - 1);
	num = Number((num / Math.pow(1000, exponent)).toFixed(2));
	unit = units[exponent];

	return (neg ? '-' : '') + num + ' ' + unit;
};