// ==UserScript==
// @name           Amazon short URL
// @namespace      graphen
// @description    Replace article URL with short Amazon permalink
// @include        /^https?:\/\/www\.amazon\.(cn|in|co\.jp|sg|fr|de|it|nl|es|co\.uk|ca|com(\.(mx|au|br))?)\/.*(dp|gp\/product|exec\/obidos\/ASIN|o\/ASIN)\/.*$/
// @icon           https://www.amazon.com/favicon.ico
// @noframes
// @grant          none
// @version        2.5
// @downloadURL none
// ==/UserScript==

/* jshint esversion: 6 */
(function (doc) {
  'use strict';
  var asinId = doc.getElementById('ASIN');
  
  if (asinId) {

    asinId = asinId.value;
    history.replaceState(null, 'Amazon URL Cleaner', '/dp/' + asinId + '/');
    console.log("URL replaced by Amazon URL Cleaner. ASIN: " + asinId);
  }
  
  else {
  // Get ASIN from canonical link
    var links = doc.getElementsByTagName('link');
    
    var i;
    for (i=0; i < links.length; i++) {
      
      if (links[i].rel === 'canonical') {
      
        var canonical = links[i].href;
        var asin = canonical.replace(/https?:\/\/www\.amazon\..*\/dp\/([\w]+)$/, '$1');
        
        if (asin.length === 10) {
          history.replaceState(null, 'Amazon URL Cleaner', '/dp/' + asin + '/');
          console.log("URL replaced by Amazon URL Cleaner. ASIN: " + asin);
        }
      }
    }
  }
}) (document);