package main

import (
	"fmt"
	"log"
	"os"
	"path/filepath"

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

const Version = "0.0.1"

func main() {
	var args struct {
		Address  string `arg:"positional,required"`
		Username string `arg:"positional,required"`
		Password string `arg:"positional,required"`
		Output   string `arg:"-o" help:"Output directory" default:"mail"`
	}

	if err := arg.Parse(&args); err != nil {
		switch err {
		case arg.ErrHelp:
			fmt.Print(help)
			os.Exit(0)
		case arg.ErrVersion:
			fmt.Print(version)
			os.Exit(0)
		}

		fmt.Println(err.Error())
		os.Exit(-1)
	}

	c, err := client.DialTLS(args.Address, nil)
	if err != nil {
		log.Fatalln(err.Error())
	}
	defer c.Logout()

	if err := c.Login(args.Username, args.Password); err != nil {
		log.Fatalln(err.Error())
	}

	mailboxes, err := Mailboxes(c)
	if err != nil {
		log.Fatalln(err.Error())
	}

	for _, m := range mailboxes {
		if m.Name == "Trash" {
			log.Println("Skipping Trash")
			continue
		}

		log.Println(m.Name)
		if err := FetchMailbox(c, m, args.Output); err != nil {
			log.Fatalln(err.Error())
		}
	}
}

/* Get list of Mailboxes. */
func Mailboxes(c *client.Client) ([]*imap.MailboxInfo, error) {
	ch := make(chan *imap.MailboxInfo, 6)
	done := make(chan error, 1)

	go func() { done <- c.List("", "*", ch) }()

	var mailboxes []*imap.MailboxInfo
	for m := range ch {
		mailboxes = append(mailboxes, m)
	}

	if err := <-done; err != nil {
		return nil, err
	}

	return mailboxes, nil
}

func FetchMailbox(c *client.Client, mailbox *imap.MailboxInfo, dir string) error {
	mbox, err := c.Select(mailbox.Name, true)
	if err != nil {
		return err
	}

	if err := os.MkdirAll(filepath.Join(dir, mailbox.Name), 0o777); err != nil {
		return err
	}

	if mbox.Messages == 0 {
		return nil
	}

	seqset := new(imap.SeqSet)
	seqset.AddRange(1, mbox.Messages)

	section := &imap.BodySectionName{Peek: false}
	items := []imap.FetchItem{imap.FetchAll, section.FetchItem()}

	messages := make(chan *imap.Message, 10)
	done := make(chan error, 1)

	go func() {
		done <- c.Fetch(seqset, items, messages)
	}()

	for msg := range messages {
		body := msg.GetBody(section)
		if body == nil {
			return fmt.Errorf("message body is nil")
		}

		data := make([]byte, body.Len())
		if _, err := body.Read(data); err != nil {
			return err
		}

		file, err := os.Create(
			filepath.Join(dir, mailbox.Name, fmt.Sprintf(
				"%s_%d.eml", msg.InternalDate.UTC().Format("20060102T150405Z"), msg.SeqNum,
			)),
		)
		if err != nil {
			return err
		}

		if _, err := file.Write(data); err != nil {
			file.Close()
			return err
		}

		log.Println(mailbox.Name, "->", msg.Envelope.Subject)
		file.Close()
	}

	if err := <-done; err != nil {
		return err
	}

	return nil
}

const help = ``
const version = "backup-imap, version " + Version + "\n"