package main

import (
	"crypto/tls"
	"encoding/base64"
	"fmt"
	"io/ioutil"
	"log"
	"mime"
	"net"
	"net/mail"
	"net/smtp"
	"path/filepath"
)

const (
	MIME = "MIME-version: 1.0;\nContent-Type: text/html; charset=\"UTF-8\";\n\n"
)

// Attachment represents an email attachment.
type Attachment struct {
	Filename string
	Data     []byte
}

type Message struct {
	Attachments map[string]*Attachment
}

func (m *Message) attach(file string) error {
	data, err := ioutil.ReadFile(file)
	if err != nil {
		return err
	}

	_, filename := filepath.Split(file)

	m.Attachments[filename] = &Attachment{
		Filename: filename,
		Data:     data,
	}

	return nil
}

// SSL/TLS Email Example
func main() {

	m := &Message{}

	m.Attachments = make(map[string]*Attachment)

	// 이거 smtp 서버랑 주소 안 맞으면 거부됩니다. 네이버면 아이디@naver.com 그리고 mail.Address 첫번째 공백은 이름인데 없어도 됨
	from := mail.Address{"", "보내는 메일 주소"}
	to := mail.Address{"", "받는 메일 주소"}
	subj := "This is the email subject 나여나"
	body := "This is an example body.<br> With two lines. <br>내용이여.."

	// Setup headers
	headers := make(map[string]string)
	headers["From"] = from.String()
	headers["To"] = to.String()
	headers["Subject"] = subj

	// Setup message
	message := ""
	for k, v := range headers {
		message += fmt.Sprintf("%s: %s\r\n", k, v)
	}

	fileman := []string{"1.png", "2.png", "3.pdf"}

	// add attachments
	for k := 0; k < len(fileman); k++ {
		if err := m.attach(fileman[k]); err != nil {
			log.Fatal(err)
		}
	}

	boundary := "f46d043c813270fc6b04c2d223da"

	if len(m.Attachments) > 0 {
		message += "Content-Type: multipart/mixed; boundary=" + boundary + "\r\n"
		message += "\r\n--" + boundary + "\r\n"
	}

	message += MIME + "\r\n" + body

	if len(m.Attachments) > 0 {

		for _, attachment := range m.Attachments {
			message += "\r\n\r\n--" + boundary + "\r\n"

			ext := filepath.Ext(attachment.Filename)
			mimetype := mime.TypeByExtension(ext)
			if mimetype != "" {
				mime := fmt.Sprintf("Content-Type: %s\r\n", mimetype)
				message += mime
			} else {
				message += "Content-Type: application/octet-stream\r\n"
			}
			message += "Content-Transfer-Encoding: base64\r\n"

			message += "Content-Disposition: attachment; filename=\"=?UTF-8?B?"
			message += base64.StdEncoding.EncodeToString([]byte(attachment.Filename))
			message += "?=\"\r\n\r\n"

			b := make([]byte, base64.StdEncoding.EncodedLen(len(attachment.Data)))
			base64.StdEncoding.Encode(b, attachment.Data)

			message += string(b)

			message += "\r\n--" + boundary
		}

		message += "--"
	}

	// Connect to the SMTP Server
	servername := "smtp 주소:465"

	host, _, _ := net.SplitHostPort(servername)

	auth := smtp.PlainAuth("", "아이디", "패스워드", host)

	// TLS config
	tlsconfig := &tls.Config{
		InsecureSkipVerify: true,
		ServerName:         host,
	}

	// Here is the key, you need to call tls.Dial instead of smtp.Dial
	// for smtp servers running on 465 that require an ssl connection
	// from the very beginning (no starttls)
	conn, err := tls.Dial("tcp", servername, tlsconfig)
	if err != nil {
		log.Panic(err)
	}

	c, err := smtp.NewClient(conn, host)
	if err != nil {
		log.Panic(err)
	}

	// Auth
	if err = c.Auth(auth); err != nil {
		log.Panic(err)
	}

	// To && From
	if err = c.Mail(from.Address); err != nil {
		log.Panic(err)
	}

	if err = c.Rcpt(to.Address); err != nil {
		log.Panic(err)
	}

	// Data
	w, err := c.Data()
	if err != nil {
		log.Panic(err)
	}

	_, err = w.Write([]byte(message))
	if err != nil {
		log.Panic(err)
	}

	err = w.Close()
	if err != nil {
		log.Panic(err)
	}

	c.Quit()

}