// ==UserScript==
// @name         东立漫画下载
// @namespace    http://tampermonkey.net/
// @version      0.1
// @description  自动下载电子书城的漫画
// @author       shadows
// @license      MIT License
// @match        https://ebook.tongli.com.tw/reader/FireBase2.html?bookID=*
// @icon         https://ebook.tongli.com.tw/images/logo_small.jpg
// @grant        none
// @require      https://gcore.jsdelivr.net/npm/jszip@3.6.0/dist/jszip.min.js
// @require      https://gcore.jsdelivr.net/npm/file-saver@2.0.2/dist/FileSaver.min.js
// @run-at       document-end
// @downloadURL none
// ==/UserScript==
"use strict";
(async () => {
while (document.getElementById("page0") == null) {
    await new Promise(r => setTimeout(r, 2000));
}
while (localStorage.getItem("Pages") == null) {
    await new Promise(r => setTimeout(r, 1000));
}

let name = document.title;
let imagesData = JSON.parse(localStorage.getItem("Pages"));
let images = await downloadImages(imagesData, name);
let zip = new JSZip();
let targetLength = images.length.toString().length;
for (let image of images) {
    zip.file(`${image.id.toString().padStart(targetLength,'0')}.jpg`, image.ontent);
}
zip.generateAsync({ type: "blob", base64: true }).then(content => saveAs(content, `${name}.zip`));


function downloadImages(imagesData, name) {

    async function downloadSingleImage(item) {
        return fetch(item.ImageURL).then(res => res.blob()).then(blob => {
            console.log(`${name}-${item.PageNumber} have downloaded.`);
            //返回包含id drm_hash与图片数据的对象
            return { id: item.PageNumber, ontent: blob };
        });
    }

    let images = asyncPool(10, imagesData, downloadSingleImage);
    return images;
}
/**
 * @param poolLimit 并发控制数 (>= 1)
 * @param array 参数数组
 * @param iteratorFn 异步任务，返回 promise 或是 async 方法
 * https://www.luanzhuxian.com/post/60c2c548.html
 */
function asyncPool(poolLimit, array, iteratorFn) {
    let i = 0
    const ret = [] // Promise.all(ret) 的数组
    const executing = []
    const enqueue = function() {
        // array 遍历完，进入 Promise.all 流程
        if (i === array.length) {
            return Promise.resolve()
        }

        // 每调用一次 enqueue，就初始化一个 promise，并放入 ret 队列
        const item = array[i++]
        const p = Promise.resolve().then(() => iteratorFn(item, array))
        ret.push(p)

        // 插入 executing 队列，即正在执行的 promise 队列，并且 promise 执行完毕后，会从 executing 队列中移除
        const e = p.then(() => executing.splice(executing.indexOf(e), 1))
        executing.push(e)

        // 每当 executing 数组中 promise 数量达到 poolLimit 时，就利用 Promise.race 控制并发数，完成的 promise 会从 executing 队列中移除，并触发 Promise.race 也就是 r 的回调，继续递归调用 enqueue，继续 加入新的 promise 任务至 executing 队列
        let r = Promise.resolve()
        if (executing.length >= poolLimit) {
            r = Promise.race(executing)
        }

        // 递归，链式调用，直到遍历完 array
        return r.then(() => enqueue())
    }

    return enqueue().then(() => Promise.all(ret))
}
})();