'use strict';
  var stripAnsi = require('strip-ansi');
  var codePointAt = require('code-point-at');
  var isFullwidthCodePoint = require('is-fullwidth-code-point');
  
  // https://github.com/nodejs/io.js/blob/cff7300a578be1b10001f2d967aaedc88aee6402/lib/readline.js#L1345
  module.exports = function (str) {
  	if (typeof str !== 'string' || str.length === 0) {
  		return 0;
  	}
  
  	var width = 0;
  
  	str = stripAnsi(str);
  
  	for (var i = 0; i < str.length; i++) {
  		var code = codePointAt(str, i);
  
  		// ignore control characters
  		if (code <= 0x1f || (code >= 0x7f && code <= 0x9f)) {
  			continue;
  		}
  
  		// surrogates
  		if (code >= 0x10000) {
  			i++;
  		}
  
  		if (isFullwidthCodePoint(code)) {
  			width += 2;
  		} else {
  			width++;
  		}
  	}
  
  	return width;
  };