// ==UserScript==
// @name        Amazon CPU Tamer
// @name:ja     Amazon CPU Tamer
// @name:zh-CN  Amazon CPU Tamer
// @namespace   knoa.jp
// @contributionURL https://paypal.me/kantankikaku
// @description It reduces CPU usage on Amazon shopping pages. Enjoy your snappy shopping.
// @description:ja AmazonのショッピングページでのCPU使用率を削減します。お買いものをサクサク楽しみましょう。
// @description:zh-CN 减少Amazon购物页面上的CPU利用率。顺利地享受买东西吧。
// @include     https://www.amazon.com/*
// @include     https://www.amazon.co.jp/*
// @include     https://www.amazon.co.uk/*
// @include     https://www.amazon.*
// @include     https://*.amazon-*.com/*
// @include     https://*.*-amazon.com/*
// @exclude     */cart/*
// @exclude     */buy/*
// @version     1.3.1
// @grant       none
// @run-at      document-start
// @downloadURL none
// ==/UserScript==

/*
[update]
Minor fix.

[memo]
top:    interval さまざま多数, timeout インタラクションのみで定常なし
iframe: interval なし,         timeout 定常 100ms が iframe ごとに1つずつ
*/
(function(){
  const SCRIPTID = 'AmazonCpuTamer';
  console.log(SCRIPTID, location.href);
  const TAMEDINTERVAL = 60*1000;/* a bunch of intervals does cost so much even if the processes do nothing */
  const QUICKRESPONSE =  1*1000;/* some of the interactions need rather quick response such as video guides */
  const IFRAMETIMEOUT =  1*1000;/* amazon uses timeouts instead of intervals on iframes */
  /* tame quick intervals */
  const originalSetInterval = window.setInterval.bind(window);
  window.setInterval = function(f, interval, ...args){
    if(interval < TAMEDINTERVAL){
      console.log(SCRIPTID, 'interval:', interval, 'to', TAMEDINTERVAL, location.href);
      interval = TAMEDINTERVAL;
      window.setTimeout(f, QUICKRESPONSE, ...args);
    }
    return originalSetInterval(f, interval, ...args);
  };
  /* tame quick timeouts on iframe ads */
  if(window !== top){
    const originalSetTimeout = window.setTimeout.bind(window);
    window.setTimeout = function(f, timeout, ...args){
      if(document.hidden) return;
      if(timeout < IFRAMETIMEOUT){
        //console.log(SCRIPTID, 'timeout:', timeout, 'to', IFRAMETIMEOUT, location.href);
        timeout = IFRAMETIMEOUT;
      }
      return originalSetTimeout(f, timeout, ...args);
    };
  }
  /* add an associate tag */
  switch(location.host){
    case('www.amazon.com'):
      addTag('knoa-20');
      break;
    case('www.amazon.co.uk'):
      addTag('knoa-21');
      break;
    case('www.amazon.co.jp'):
      addTag('knoa-22');
      break;
  }
  function addTag(tag){
    const url = new URL(location.href);
    if(url.searchParams.get('tag') !== null) return;/* do not overwrite */
    console.log(SCRIPTID, 'associate tag:', tag);
    document.documentElement.addEventListener('mousedown', function(e){
      for(let target = e.target; target; target = target.parentNode){
        if(target.href && target.href.startsWith(location.origin)){
          const separator = (target.href.includes('?')) ? '&' : '?';
          target.href = target.href + separator + 'tag=' + tag;
        }
      }
    });
    const separator = (url.search === '') ? '?' : '&';
    history.replaceState(null, document.title, location.href + separator + 'tag=' + tag);
  }
})();