// ==UserScript==
// @name         下载知乎视频
// @version      0.9
// @description  为知乎的视频播放器添加下载功能
// @author       Chao
// @include      *://www.zhihu.com/*
// @match        *://www.zhihu.com/*
// @include      https://v.vzuu.com/video/*
// @match        https://v.vzuu.com/video/*
// @connect      zhihu.com
// @connect      vzuu.com
// @grant        GM_download
// @namespace    https://greasyfork.org/users/38953
// @downloadURL none
// ==/UserScript==
/* jshint esversion: 6 */

(async () => {
    if (window.location.host == 'www.zhihu.com') return;

    const playlistBaseUrl = 'https://lens.zhihu.com/api/videos/';
    const videoId = window.location.pathname.split('/').pop(); // 视频id
    const menuStyle = 'transform:none !important; left:auto !important; right:-0.5em !important;';
    const controlBarSelector = '#player > div:first-child > div:last-child > div:last-child > div:first-child';
    const svgDownload = '<path d="M9.5,4 H14.5 V10 H17.8 L12,15.8 L6.2,10 H9.5 Z M6.2,18 H17.8 V20 H6.2 Z"></path>';
    const svgCircle = '<circle cx="12" cy="12" r="8" fill="none" stroke-width="2" stroke="#555" />' +
        '<text x="50%" y="50%" dy=".4em" text-anchor="middle" fill="#fff" font-size="9">0</text>' +
        '<path fill="none" r="8" transform="translate(12,12)" stroke-width="2" stroke="#fff" />';
    const domControlBar = document.querySelector(controlBarSelector);
    const domFullScreenBtn = document.querySelector(controlBarSelector + '> div:nth-last-of-type(1)');
    const domResolutionBtn = document.querySelector(controlBarSelector + '> div:nth-last-of-type(3)');
    let domDownloadBtn = domResolutionBtn.cloneNode(true); // 克隆分辨率按钮为下载按钮
    let domMenuItem = domDownloadBtn.querySelectorAll('button')[1];
    let domMenu = domMenuItem.parentNode;
    let videos = []; // 存储各分辨率的视频信息
    let blobs = null; // 存储视频段
    let ratio;
    let errors = 0;

    function wait(time) {
        return new Promise(function (resolve, reject) {
            setTimeout(resolve, time);
        });
    }

    function fetchRetry(url, options = {}, times = 1, delay = 1000, checkStatus = true) {
        return new Promise((resolve, reject) => {
            // fetch 成功处理函数
            function success(res) {
                if (checkStatus && !res.ok) {
                    failure(res);
                } else {
                    resolve(res);
                }
            }

            // 单次失败处理函数
            function failure(error) {
                times--;

                if (times) {
                    setTimeout(fetchUrl, delay);
                }
                else {
                    reject(error);
                }
            }

            // 总体失败处理函数
            function finalHandler(error) {
                throw error;
            }

            function fetchUrl() {
                return fetch(url, options)
                    .then(success)
                    .catch(failure)
                    .catch(finalHandler);
            }

            fetchUrl();
        });
    }

    function fileSize(size) {
        let n = Math.log(size) / Math.log(1024) | 0;
        return (size / Math.pow(1024, n)).toFixed(0) + ' ' + (n ? 'KMGTPEZY'[--n] + 'B' : 'Bytes');
    }

    // 下载 m3u8 文件
    async function downloadM3u8(url) {
        const res = await fetchRetry(url, {}, 3);
        const m3u8 = await res.text();
        let i = 0;

        blobs = [];
        ratio = 0;
        errors = 0;

        // 初始化进度显示
        domDownloadBtn.querySelector('svg').innerHTML = svgCircle;

        m3u8.split('\n').forEach(function (line) {
            if (line.match(/\.ts/)) {
                blobs[i] = undefined;
                downloadTs(url.replace(/\/[^\/]+?$/, '/' + line), i++);
            }
        });
    }

    // 下载 m3u8 文件中的单个 ts 文件
    async function downloadTs(url, order) {
        let res;
        let blob;

        try {
            res = await fetchRetry(url, {}, 5);
            blob = await res.blob();
        } catch (e) {
            if (++errors == 1) {
                resetDownloadIcon();
                alert('下载视频失败，请重新下载。');
            }
            return;
        }

        ratio++;
        blobs[order] = blob;

        errors ? resetDownloadIcon() : updateProgress(Math.round(100 * ratio / blobs.length));

        store();
    }

    // 保存视频文件
    function store() {
        for (let [index, blob] of blobs.entries()) {
            if (blob === undefined) return;
        }

        let blob = new Blob(blobs, {type: 'video/h264'}),
            name = (new Date()).valueOf() + '.mp4',
            url = window.URL.createObjectURL(blob),
            userAgent = window.navigator.userAgent;

        blobs = null;

        // 结束进度显示
        resetDownloadIcon();

        // edge
        if (window.navigator && window.navigator.msSaveBlob) {
            window.navigator.msSaveBlob(blob, name);
        }
        else {
            url = window.URL.createObjectURL(blob);

            // Chrome 可以使用 Tampermonkey 的 GM_download 函数绕过 CSP(Content Security Policy) 的限制
            if (userAgent.indexOf('Chrome') > 0 && window.GM_download) {
                GM_download({url, name});
            }
            else {
                // firefox 需要禁用 CSP, about:config -> security.csp.enable => false
                // violentmonkey(暴力猴)没有 GM_download 函数
                var a = document.createElement('a');
                document.body.appendChild(a);
                a.href = url;
                a.download = name;
                //a.target = '_blank';
                a.click();
                document.body.removeChild(a);

                setTimeout(function () {
                    window.URL.revokeObjectURL(url);
                }, 100);
            }
        }
    }

    // 重置下载图标
    function resetDownloadIcon() {
        domDownloadBtn.querySelector('svg').innerHTML = svgDownload;
    }

    // 更新下载进度界面
    function updateProgress(percent) {
        let r = 8;
        let degrees = percent / 100 * 360; // 进度对应的角度值
        let rad = degrees * (Math.PI / 180); // 角度对应的弧度值
        let x = (Math.sin(rad) * r).toFixed(2); // 极坐标转换成直角坐标
        let y = -(Math.cos(rad) * r).toFixed(2);
        let lenghty = Number(degrees > 180); // 大于180°时画大角度弧，小于180°时画小角度弧，(deg > 180) ? 1 : 0
        let paths = ['M', 0, -r, 'A', r, r, 0, lenghty, 1, x, y]; // path 属性

        domDownloadBtn.querySelector('svg > path').setAttribute('d', paths.join(' '));
        domDownloadBtn.querySelector('svg > text').textContent = percent;
    }

    //await wait(500);

    // 读取 playlist
    const res = await fetchRetry(playlistBaseUrl + videoId, {
        headers: {
            'referer': 'refererBaseUrl + videoId',
            'authorization': 'oauth c3cef7c66a1843f8b3a9e6a1e3160e20' // in zplayer.min.js of zhihu
        }
    }, 3);
    const videoInfo = await res.json();

    // 获取不同分辨率视频的信息
    for (let [key, video] of Object.entries(videoInfo.playlist)) {
        video.name = key;
        videos.push(video);
    }

    // 按分辨率大小排序
    videos = videos.sort(function (v1, v2) {
        return v1.width == v2.width ? 0 : (v1.width > v2.width ? 1 : -1);
    }).reverse();

    // 生成下载按钮图标
    domDownloadBtn.querySelector('button:first-child').outerHTML = domFullScreenBtn.cloneNode(true).querySelector('button').outerHTML;
    domDownloadBtn.querySelector('svg').innerHTML = svgDownload;

    // 生成各分辨率菜单
    domMenuItem.className = domMenuItem.className.split('-').shift();
    domMenuItem.parentNode.innerHTML = '';
    for (let [index, video] of videos.entries()) {
        let node = domMenuItem.cloneNode();
        node.innerHTML = video.width + ' (' + fileSize(video.size) + ')';
        node.style.width = '100%';
        node.style.textAlign = 'right';
        node.dataset.videoIndex = index;
        domMenu.appendChild(node);
    }

    // 鼠标事件 - 显示菜单
    domDownloadBtn.addEventListener('pointerenter', () => {
        if (blobs === null) {
            domMenu.parentNode.style.cssText = menuStyle + 'opacity:1 !important; visibility:visible !important';
        }
    });

    // 鼠标事件 - 隐藏菜单
    domDownloadBtn.addEventListener('pointerleave', () => {
        if (blobs === null) {
            domMenu.parentNode.style.cssText = menuStyle;
        }
    });

    // 鼠标事件 - 暂停下载
    // domDownloadBtn.addEventListener('pointerdown', () => {});

    // 鼠标事件 - 选择菜单项
    domDownloadBtn.addEventListener('pointerup', event => {
        let e = event.srcElement || event.target;
        let video;

        if (e.tagName == 'BUTTON' && !e.children.length) {
            video = videos[e.dataset.videoIndex];

            // 隐藏菜单
            domMenu.dispatchEvent(new MouseEvent('pointerleave', {
                'bubbles': true,
                'cancelable': true
            }));

            downloadM3u8(video.play_url);
        }
    });

    // 显示下载按钮
    domControlBar.appendChild(domDownloadBtn);
})();