// Copyright 2014 The Gogs Authors. All rights reserved.
// Use of this source code is governed by a MIT-style
// license that can be found in the LICENSE file.

package mailer

import (
	"crypto/tls"
	"fmt"
	"net"
	"net/mail"
	"net/smtp"
	"os"
	"strings"

	"github.com/gogits/gogs/modules/log"
	"github.com/gogits/gogs/modules/setting"
)

type loginAuth struct {
	username, password string
}

// SMTP AUTH LOGIN Auth Handler
func LoginAuth(username, password string) smtp.Auth {
	return &loginAuth{username, password}
}

func (a *loginAuth) Start(server *smtp.ServerInfo) (string, []byte, error) {
	return "LOGIN", []byte{}, nil
}

func (a *loginAuth) Next(fromServer []byte, more bool) ([]byte, error) {
	if more {
		switch string(fromServer) {
		case "Username:":
			return []byte(a.username), nil
		case "Password:":
			return []byte(a.password), nil
		default:
			return nil, fmt.Errorf("unknwon fromServer: %s", string(fromServer))
		}
	}
	return nil, nil
}

type Message struct {
	To      []string
	From    string
	Subject string
	ReplyTo string
	Body    string
	Type    string
	Massive bool
	Info    string
}

// create mail content
func (m Message) Content() string {
	// set mail type
	contentType := "text/plain; charset=UTF-8"
	if m.Type == "html" {
		contentType = "text/html; charset=UTF-8"
	}

	// create mail content
	content := "From: " + m.From + "\r\nReply-To: " + m.ReplyTo + "\r\nSubject: " + m.Subject + "\r\nContent-Type: " + contentType + "\r\n\r\n" + m.Body
	return content
}

var mailQueue chan *Message

func NewContext() {
	if setting.MailService == nil {
		return
	}

	mailQueue = make(chan *Message, setting.MailService.QueueLength)
	go processMailQueue()
}

func processMailQueue() {
	for {
		select {
		case msg := <-mailQueue:
			num, err := Send(msg)
			tos := strings.Join(msg.To, ", ")
			info := ""
			if err != nil {
				if len(msg.Info) > 0 {
					info = ", info: " + msg.Info
				}
				log.Error(4, fmt.Sprintf("Async sent email %d succeed, not send emails: %s%s err: %s", num, tos, info, err))
			} else {
				log.Trace(fmt.Sprintf("Async sent email %d succeed, sent emails: %s%s", num, tos, info))
			}
		}
	}
}

// sendMail allows mail with self-signed certificates.
func sendMail(settings *setting.Mailer, recipients []string, msgContent []byte) error {
	host, port, err := net.SplitHostPort(settings.Host)
	if err != nil {
		return err
	}

	tlsconfig := &tls.Config{
		InsecureSkipVerify: settings.SkipVerify,
		ServerName:         host,
	}

	if settings.UseCertificate {
		cert, err := tls.LoadX509KeyPair(settings.CertFile, settings.KeyFile)
		if err != nil {
			return err
		}
		tlsconfig.Certificates = []tls.Certificate{cert}
	}

	conn, err := net.Dial("tcp", net.JoinHostPort(host, port))
	if err != nil {
		return err
	}
	defer conn.Close()

	isSecureConn := false
	// Start TLS directly if the port ends with 465 (SMTPS protocol)
	if strings.HasSuffix(port, "465") {
		conn = tls.Client(conn, tlsconfig)
		isSecureConn = true
	}

	client, err := smtp.NewClient(conn, host)
	if err != nil {
		return err
	}

	if !setting.MailService.DisableHelo {
		hostname := setting.MailService.HeloHostname
		if len(hostname) == 0 {
			hostname, err = os.Hostname()
			if err != nil {
				return err
			}
		}

		if err = client.Hello(hostname); err != nil {
			return err
		}
	}

	// If not using SMTPS, alway use STARTTLS if available
	hasStartTLS, _ := client.Extension("STARTTLS")
	if !isSecureConn && hasStartTLS {
		if err = client.StartTLS(tlsconfig); err != nil {
			return err
		}
	}

	canAuth, options := client.Extension("AUTH")

	if canAuth && len(settings.User) > 0 {
		var auth smtp.Auth

		if strings.Contains(options, "CRAM-MD5") {
			auth = smtp.CRAMMD5Auth(settings.User, settings.Passwd)
		} else if strings.Contains(options, "PLAIN") {
			auth = smtp.PlainAuth("", settings.User, settings.Passwd, host)
		} else if strings.Contains(options, "LOGIN") {
			// Patch for AUTH LOGIN
			auth = LoginAuth(settings.User, settings.Passwd)
		}

		if auth != nil {
			if err = client.Auth(auth); err != nil {
				return err
			}
		}
	}

	if fromAddress, err := mail.ParseAddress(settings.From); err != nil {
		return err
	} else {
		if err = client.Mail(fromAddress.Address); err != nil {
			return err
		}
	}

	for _, rec := range recipients {
		if err = client.Rcpt(rec); err != nil {
			return err
		}
	}

	w, err := client.Data()
	if err != nil {
		return err
	}
	if _, err = w.Write([]byte(msgContent)); err != nil {
		return err
	}

	if err = w.Close(); err != nil {
		return err
	}

	return client.Quit()
}

// Direct Send mail message
func Send(msg *Message) (int, error) {
	log.Trace("Sending mails to: %s", strings.Join(msg.To, ", "))

	// get message body
	content := msg.Content()

	if len(msg.To) == 0 {
		return 0, fmt.Errorf("empty receive emails")
	} else if len(msg.Body) == 0 {
		return 0, fmt.Errorf("empty email body")
	}

	if msg.Massive {
		// send mail to multiple emails one by one
		num := 0
		for _, to := range msg.To {
			body := []byte("To: " + to + "\r\n" + content)
			err := sendMail(setting.MailService, []string{to}, body)
			if err != nil {
				return num, err
			}
			num++
		}
		return num, nil
	} else {
		body := []byte("To: " + strings.Join(msg.To, ",") + "\r\n" + content)

		// send to multiple emails in one message
		err := sendMail(setting.MailService, msg.To, body)
		if err != nil {
			return 0, err
		} else {
			return 1, nil
		}
	}
}

// Async Send mail message
func SendAsync(msg *Message) {
	go func() {
		mailQueue <- msg
	}()
}

// Create html mail message
func NewHtmlMessage(To []string, From, Subject, Body string) Message {
	return Message{
		To:      To,
		From:    setting.MailService.From,
		ReplyTo: From,
		Subject: Subject,
		Body:    Body,
		Type:    "html",
	}
}