/*!
   * encodeurl
   * Copyright(c) 2016 Douglas Christopher Wilson
   * MIT Licensed
   */
  
  'use strict'
  
  /**
   * Module exports.
   * @public
   */
  
  module.exports = encodeUrl
  
  /**
   * RegExp to match non-URL code points, *after* encoding (i.e. not including "%")
   * and including invalid escape sequences.
   * @private
   */
  
  var ENCODE_CHARS_REGEXP = /(?:[^\x21\x25\x26-\x3B\x3D\x3F-\x5B\x5D\x5F\x61-\x7A\x7E]|%(?:[^0-9A-Fa-f]|[0-9A-Fa-f][^0-9A-Fa-f]))+/g
  
  /**
   * RegExp to match unmatched surrogate pair.
   * @private
   */
  
  var UNMATCHED_SURROGATE_PAIR_REGEXP = /(^|[^\uD800-\uDBFF])[\uDC00-\uDFFF]|[\uD800-\uDBFF]([^\uDC00-\uDFFF]|$)/g
  
  /**
   * String to replace unmatched surrogate pair with.
   * @private
   */
  
  var UNMATCHED_SURROGATE_PAIR_REPLACE = '$1\uFFFD$2'
  
  /**
   * Encode a URL to a percent-encoded form, excluding already-encoded sequences.
   *
   * This function will take an already-encoded URL and encode all the non-URL
   * code points. This function will not encode the "%" character unless it is
   * not part of a valid sequence (`%20` will be left as-is, but `%foo` will
   * be encoded as `%25foo`).
   *
   * This encode is meant to be "safe" and does not throw errors. It will try as
   * hard as it can to properly encode the given URL, including replacing any raw,
   * unpaired surrogate pairs with the Unicode replacement character prior to
   * encoding.
   *
   * @param {string} url
   * @return {string}
   * @public
   */
  
  function encodeUrl (url) {
    return String(url)
      .replace(UNMATCHED_SURROGATE_PAIR_REGEXP, UNMATCHED_SURROGATE_PAIR_REPLACE)
      .replace(ENCODE_CHARS_REGEXP, encodeURI)
  }