package email

import (
	"context"
	"fmt"
	"net"
	"net/smtp"
	"strings"
)

var smtpSendMail = smtp.SendMail

type smtpTransport struct {
	host     string
	port     string
	user     string
	password string
}

func newSMTPTransport(host, port, user, password string) *smtpTransport {
	if strings.TrimSpace(port) == "" {
		port = "587"
	}
	return &smtpTransport{host: host, port: port, user: user, password: password}
}

func (s *smtpTransport) Name() string { return ProviderSMTP }

func (s *smtpTransport) Send(ctx context.Context, from FromIdentity, msg Outbound) error {
	_ = ctx
	to := strings.TrimSpace(msg.To)
	if to == "" {
		return ErrInvalidRecipient
	}
	if hasHeaderBreak(to) {
		return ErrInvalidRecipient
	}
	fromAddr := strings.TrimSpace(from.Email)
	if fromAddr == "" {
		return ErrInvalidFrom
	}
	if hasHeaderBreak(fromAddr) || hasHeaderBreak(from.Name) {
		return ErrInvalidFrom
	}
	if hasHeaderBreak(msg.Subject) {
		return fmt.Errorf("invalid subject")
	}
	replyTo := strings.TrimSpace(from.ReplyTo)
	if replyTo != "" && hasHeaderBreak(replyTo) {
		return fmt.Errorf("invalid reply-to")
	}
	addr := net.JoinHostPort(s.host, s.port)
	boundary := "descrybe_mkt_7f3a"
	var body strings.Builder
	body.WriteString(fmt.Sprintf("From: %s\r\n", from.Formatted()))
	body.WriteString(fmt.Sprintf("To: %s\r\n", to))
	body.WriteString(fmt.Sprintf("Subject: %s\r\n", msg.Subject))
	if replyTo != "" {
		body.WriteString(fmt.Sprintf("Reply-To: %s\r\n", replyTo))
	}
	for k, v := range msg.Headers {
		k = strings.TrimSpace(k)
		v = strings.TrimSpace(v)
		if k == "" || v == "" {
			continue
		}
		if hasHeaderBreak(k) || strings.Contains(k, ":") {
			return fmt.Errorf("invalid header name")
		}
		if hasHeaderBreak(v) {
			return fmt.Errorf("invalid header value")
		}
		body.WriteString(fmt.Sprintf("%s: %s\r\n", k, v))
	}
	body.WriteString("MIME-Version: 1.0\r\n")
	if strings.TrimSpace(msg.HTML) != "" {
		body.WriteString(fmt.Sprintf("Content-Type: multipart/alternative; boundary=%s\r\n\r\n", boundary))
		body.WriteString(fmt.Sprintf("--%s\r\nContent-Type: text/plain; charset=UTF-8\r\n\r\n%s\r\n", boundary, msg.Text))
		body.WriteString(fmt.Sprintf("--%s\r\nContent-Type: text/html; charset=UTF-8\r\n\r\n%s\r\n", boundary, msg.HTML))
		body.WriteString(fmt.Sprintf("--%s--\r\n", boundary))
	} else {
		body.WriteString("Content-Type: text/plain; charset=UTF-8\r\n\r\n")
		body.WriteString(msg.Text)
	}

	var auth smtp.Auth
	if s.user != "" {
		auth = smtp.PlainAuth("", s.user, s.password, s.host)
	}
	if err := smtpSendMail(addr, auth, fromAddr, []string{to}, []byte(body.String())); err != nil {
		return fmt.Errorf("smtp send failed")
	}
	return nil
}

func hasHeaderBreak(v string) bool {
	return strings.ContainsAny(v, "\r\n")
}