edown

// ==UserScript==
// @name         Ebookjapan hacker
// @namespace    http://tampermonkey.net/
// @version      0.1
// @description  try to take over the world!
// @author       You
// @match        https://ebookjapan.yahoo.co.jp/bviewer/purchased/*
// @match        https://ebookjapan.yahoo.co.jp/bviewer/trial/*
// @grant        none
// ==/UserScript==

(function() {
  const showTips = {
    info (msg) {
      console.log('%c' + msg, 'color:blue');
    },
    success (msg) {
      console.log('%c' + msg, 'color:green');
    },
    error (msg) {
      console.log('%c' + msg, 'color:red');
    }
  }

  const delayExec = function(fn, delay) {
    let timer = null
    let context

    return function(...args) {
      context = this
      if (timer) {
        clearTimeout(timer)
      }

      timer = setTimeout(() => {
        fn.apply(context, args)
        timer = null
      }, delay)
    }
  }

  const rename = num => num > 99 ? num : num > 9 ? '0' + num : '00' + num;

  const downloadPage = (resolve, index) => {
    return function(blob) {
      const a = document.createElement('a');
      a.download = rename(index);
      a.href = window.URL.createObjectURL(blob);
      a.click();
      window.URL.revokeObjectURL(a.href);
      resolve();
    }
  }

  let toBlob; // 取回canvas元素转换为二进制文件的API
  let getImageData;
  let viewerCanvas;

  {
    const iframe = document.createElement('iframe');
    iframe.style.display = "none";

    iframe.onload = e => {
      toBlob = iframe.contentWindow.HTMLCanvasElement.prototype.toBlob;
      getImageData = iframe.contentWindow.CanvasRenderingContext2D.prototype.getImageData;


      window.HTMLCanvasElement.prototype.toBlob = toBlob;
      window.CanvasRenderingContext2D.prototype.getImageData = getImageData;

      showTips.success('iframe load success')
    }

    document.body.appendChild(iframe);
  }

  const getCanvas = function(whiteBorder = false, index) {
    console.log(index)
    const newCanvas = document.createElement('canvas')
    newCanvas.width = viewerCanvas.width - (whiteBorder ? 1 : 0)
    newCanvas.height = viewerCanvas.height

    const capture = getImageData.apply(viewerCanvas.getContext('2d'), [
      whiteBorder ? (index % 2 === 0 ? 1 : 0) : 0,
      0,
      viewerCanvas.width - (whiteBorder ? 1 : 0),
      viewerCanvas.height
    ]);

    newCanvas.getContext('2d').putImageData(capture, 0, 0);

    return newCanvas;
  }

  const drawed = delayExec(async function(whiteBorder, pageIndex) {
    const mimeType = 'image/png';
    const canvas = getCanvas(whiteBorder, pageIndex)
    toBlob.apply(canvas, [downloadPage(() => {}, pageIndex), mimeType]);
  }, 1500)

  window.startDownload = function (whiteBorder, pageIndex = 0) {
    const __drawImage = window.CanvasRenderingContext2D.prototype.drawImage;

    // 获取阅读器的canvas元素
    viewerCanvas = document.querySelector('.viewer > canvas');

    window.CanvasRenderingContext2D.prototype.drawImage = function(...args) {
      if (args.length !== 5) {
        return __drawImage.apply(this, args);
      }

      __drawImage.apply(this, args);
      drawed(whiteBorder, pageIndex++);
    }

    drawed(whiteBorder, pageIndex++);
  }
})();

// ==========说明==========
// 代码放到油猴去执行。
// 在调整到单页模式后（缩小浏览器窗口就能出现），每次在阅读器页面的第一页，
// 直接运行 window.startDownload() 就行了，然后缓慢手动翻页