package email

import (
	"context"
	"crypto/tls"
	"errors"
	"log"
	"net"
	"net/smtp"
	"strings"
	"time"
)

type Conn struct {
	*smtp.Client
	conn *tls.Conn
}

func Dial(ctx context.Context, addr string, auth smtp.Auth) (*Conn, error) {
	deadline, hasDeadline := ctx.Deadline()
	conn, err := tls.DialWithDialer(&net.Dialer{Deadline: deadline}, "tcp", addr, nil)
	if err != nil {
		return nil, err
	}
	if hasDeadline {
		if err := conn.SetDeadline(deadline); err != nil {
			conn.Close()
			return nil, err
		}
	}
	host, _, _ := net.SplitHostPort(addr)
	client, err := smtp.NewClient(conn, host)
	if err != nil {
		conn.Close()
		return nil, err
	}
	if auth != nil {
		if ok, _ := client.Extension("AUTH"); ok {
			if err = client.Auth(auth); err != nil {
				conn.Close()
				return nil, err
			}
		}
	}
	if hasDeadline {
		if err := conn.SetDeadline(time.Time{}); err != nil {
			conn.Close()
			return nil, err
		}
	}
	return &Conn{Client: client, conn: conn}, nil
}

func (c *Conn) Send(ctx context.Context, from string, to []string, msg []byte) (err error) {
	if err = validateLine(from); err != nil {
		return
	}
	for _, recp := range to {
		if err = validateLine(recp); err != nil {
			return
		}
	}
	if deadline, ok := ctx.Deadline(); ok {
		if err = c.conn.SetDeadline(deadline); err != nil {
			return
		}
		defer func() {
			if err2 := c.conn.SetDeadline(time.Time{}); err2 != nil {
				if err == nil {
					err = err2
				} else {
					log.Println("email: conn.SetDeadline:", err2)
				}
			}
		}()
	}
	if err = c.Mail(from); err != nil {
		return
	}
	for _, addr := range to {
		if err = c.Rcpt(addr); err != nil {
			return
		}
	}
	w, err := c.Data()
	if err != nil {
		return
	}
	defer w.Close()
	// "net/textproto".Writer will convert "\n" to "\r\n"
	_, err = w.Write(msg)
	return
}

// validateLine checks to see if a line has CR or LF as per RFC 5321
func validateLine(line string) error {
	if strings.ContainsAny(line, "\n\r") {
		return errors.New("mail: A line must not contain CR or LF")
	}
	return nil
}