app.js

var async = require('async');
var cheerio = require('cheerio');
var mkdirp = require("mkdirp");
var fs = require("fs");
var http = require("http");
var config = require("./config")
var imoocUrl = 'http://www.imooc.com/learn/'+config.lessonId;
var courseData = [];
var mainPath = config.rootPath;
//获取视频id
var getIds = (imoocUrl)=>{
	return new Promise((resolve,reject) => {
		var req = http.get(imoocUrl,(res)=>{
			var datas = "";
			res.on("data",(data)=>{
			    datas+=data
			})
			res.on("end",()=>{
				//视频id
				var videoIds = [];
		        var $ = cheerio.load(datas);
		        mainPath = mainPath + $(".course-infos h2").text().trim();
		        $('.mod-chapters .chapter').each(function (idx, element) {

					var $element = $(element);

					$element.find(".chapter-content").remove();
					//章节标题
					var courseTitle = $element.find("h3 strong").text().trim();
					//创建文件路径
					mkdirp(mainPath+"/"+courseTitle,function(err){
						if (err) {
						  return console.error(err);
						}
					});
					//课程id,名称
					var courseIds = [],fileNames = [];

					$element.find("li a").each(function(idx,element){
						var $element = $(element);
						$element.children().remove();
						var id = $element.attr('href').trim().split('video/')[1];
						var name = $element.text().replace(/\(.*\)/,'').replace(/\(.*\)/,'').replace(/\（.*\）/,"").trim();
						console.log(name)
						videoIds.push(id);courseIds.push(id);fileNames.push(name)
					})

					courseData.push({
						courseTitle:courseTitle,
						courseIds:courseIds,
						fileNames:fileNames
					})
	        	});
	        	resolve(videoIds)
			})
		});
		req.on('error', ()=>{
			reject("getIds request error")
		});
		req.end();
	})
	
}
//获取视频地址
var getUrl = (videoId)=> {
	return new Promise((resolve,reject) => {
		var videoUrl = 'http://www.imooc.com/course/ajaxmediainfo/?mid=' + videoId + '&mode=flash';
		var req = http.get(videoUrl,(res)=>{
			var datas = ""

			res.on("data",(data)=>{
			    datas+=data
			})

			res.on("end",()=>{
			   var url = JSON.parse(datas).data.result.mpath[0];
			    var video = {
			    	'url':url,
			    	'id':videoId
			    }
			    resolve(video)
			})
		})
		req.on('error', ()=>{
			console.log("getUrl request error");
		});
		req.end();
	})
}
//建立下载任务
var startDownload = (videoUrl,videoId)=>{
	return new Promise((resolve,reject) =>{
		var path;
		var fileName;
		for(var i in courseData){
	    	var courseIds = courseData[i].courseIds;
	    	for (var j in courseIds) {
	    		if(courseIds[j]==videoId){
	    			path =  mainPath + "/" + courseData[i].courseTitle + "/";
	    			fileName = courseData[i].fileNames[j] + ".mp4";
	    			console.log("开始下载:",fileName,"\r\n");
	    			break
	    		}
	    	};
		}
		var req = http.request(videoUrl,(res)=>{
			var fileBuff = [];
			res.on("data",(data)=>{
			    var buffer = new Buffer(data);
			    fileBuff.push(buffer)
			})
			var contentLength = res.headers['Content-Length']-0;
	      	res.on('end', function() {
		        var totalBuff = Buffer.concat(fileBuff);
		        if (totalBuff.length < contentLength) {
		        	startDownload(videoUrl,videoId);
		          	return console.log(videoUrl + " download error, try again");
		        }
		        fs.appendFile(path + fileName, totalBuff, function(){
					console.log("下载完毕: ",fileName,"\r\n")
				});
				resolve(null)
	      });
		})

		req.on('error', ()=>{
		 	console.log("startDownload request error,try again");
		 	startDownload(videoUrl,videoId)
		});

		req.end();
	})
}
//建立任务队列
var taskList = (videoIds)=>{
	//并发下载控制
	async.mapLimit(videoIds,config.taskNumber,function(videoId,callback){
          getUrl(videoId).then((video) =>{
    		startDownload(video.url,video.id).then(callback)
          })
    }, function (err, result) {})
}
//开始下载
getIds(imoocUrl).then((videoIds) => {
	taskList(videoIds)
}).catch((error) => {
	console.log(error)
})