package main

import (
    "flag"
    "fmt"
    "io/ioutil"
    "log"
    "math"
    "os"
    "sync"

    "github.com/emersion/go-imap"
    "github.com/emersion/go-imap/client"
)

var (
    server, email, password string
    workernum               int
    imapClient              *client.Client
    mailDirs                []string
    mailSumNums             uint32
    pagesize                int = 50
    start                   int
    stop                    int
)

type Pool struct {
    workerNum int
    road      chan *Car
    wg        sync.WaitGroup
}

//初始化这个对象
func NewPool(wn int) *Pool {
    return &Pool{workerNum: wn, road: make(chan *Car)}
}

//往channel添加具体任务
func (p *Pool) AddCar(f *Car) {
    p.road <- f
}

//goroutine去工作
func (p *Pool) work(workId int) {
    for f := range p.road {
        log.Println("workId:", workId, "start")
        f.do()
        log.Println("workId:", workId, "done")
    }
    p.wg.Done()
}

//创建goroutine等着接工作
func (p *Pool) Run() {
    for i := 0; i < p.workerNum; i++ {
        go p.work(i)
        p.wg.Add(1)
    }
    p.wg.Wait()
}

func (p *Pool) colse() {
    close(p.road)
}

var pool = NewPool(5)

func main() {
    go handleMail()
    pool.Run()
}
func handleMail() {
    //获取命令行参数
    flag.StringVar(&server, "server", "", "imap服务地址(包含端口)")
    flag.StringVar(&email, "email", "", "邮箱名")
    flag.StringVar(&password, "password", "", "密码")
    flag.Parse()
    if flag.NFlag() < 3 {
        flag.PrintDefaults()
        os.Exit(1)
    }
    if server == "" || email == "" || password == "" {
        log.Fatal("服务器地址,用户名,密码,参数错误")
    }
    //连接imap服务
    imapClient, err := client.Dial(server)
    if err != nil {
        log.Fatal(err)
    }
    //登陆
    if err := imapClient.Login(email, password); err != nil {
        log.Fatal(err)
    }
    //创建邮件夹目录
    os.Mkdir(email, os.ModePerm)
    mailboxes := make(chan *imap.MailboxInfo, 20)
    go func() {
        imapClient.List("", "*", mailboxes)
    }()
    //列取邮件夹
    for m := range mailboxes {
        mailDirs = append(mailDirs, m.Name)
    }
    //循环邮件夹,创建邮件夹目录
    for _, mailDir := range mailDirs {
        //选中每个邮件夹
        mbox, err := imapClient.Select(mailDir, false)
        if err != nil {
            log.Fatal(err)
        }
        mailDirNums := mbox.Messages
        log.Printf("%s : %d", mailDir, mailDirNums)
        fileDir := fmt.Sprintf("%s/%s", email, mailDir)
        //创建邮件夹目录
        os.Mkdir(fileDir, os.ModePerm)
        mailSumNums += mailDirNums
    }
    log.Printf("总邮件数 : %d", mailSumNums)
    //循环邮件夹,读取每个邮件夹中的邮件

    for _, mailDir := range mailDirs {
        //选中每个邮件夹
        mbox, err := imapClient.Select(mailDir, false)
        if err != nil {
            log.Fatal(err)
        }
        if mbox.Messages == 0{
            continue
        }
        //循环该邮件夹中的邮件
        pagecount := int(math.Ceil(float64(mbox.Messages) / float64(pagesize)))
        for i := 1; i <= pagecount; i++ {
            if i == 1 {
                start = 1
            } else {
                start = (i-1)*pagesize + 1
            }
            stop = i * pagesize
            if stop > int(mbox.Messages) {
                stop = int(mbox.Messages)
            }
            car := Car{
                start:      start,
                stop:       stop,
                mailDir:    mailDir,
                imapClient: imapClient,
            }
            pool.AddCar(&car)
        }
    }
    pool.colse()
}

/*具体做的事通过这个来传递*/
type Car struct {
    start, stop int
    mailDir     string
    imapClient  *client.Client
}

//具体做事
func (c *Car) do() error {
    seqset := new(imap.SeqSet)
    seqset.AddRange(uint32(c.start), uint32(c.stop))
    section := &imap.BodySectionName{}
    items := []imap.FetchItem{section.FetchItem()}

    messages := make(chan *imap.Message, pagesize)
    go func() {
        c.imapClient.Fetch(seqset, items, messages)
    }()

    for msg := range messages {
        mailFile := fmt.Sprintf("%s/%s/%d.eml", email, c.mailDir, msg.SeqNum)
        r := msg.GetBody(section)
        if r != nil {
            body, _ := ioutil.ReadAll(r)
            f, _ := os.OpenFile(mailFile, os.O_RDWR|os.O_CREATE, 0766)
            f.Write(body)
            f.Close()
            log.Printf("%s :第 %d ", c.mailDir, msg.SeqNum)
        }
    }
    return nil
}