aiaa-notification-server/internal/adapter/email.go

package adapter

import (
	"crypto/tls"
	"encoding/json"
	"fmt"
	"net"
	"net/smtp"
	"strings"

	"aiaa-notification-service/internal/config"
)

type emailConfig struct {
	To []string `json:"to"`
}

type EmailSender struct {
	cfg config.SMTPConfig
}

func NewEmailSender(cfg config.SMTPConfig) *EmailSender {
	return &EmailSender{cfg: cfg}
}

func (s *EmailSender) Type() string { return "email" }

func (s *EmailSender) Send(title, content string, config json.RawMessage) error {
	var ecfg emailConfig
	if err := json.Unmarshal(config, &ecfg); err != nil {
		return fmt.Errorf("parse email config: %w", err)
	}
	if len(ecfg.To) == 0 {
		return fmt.Errorf("email: 'to' list is empty")
	}

	msg := buildEmail(s.cfg.From, ecfg.To, title, content)
	addr := fmt.Sprintf("%s:%d", s.cfg.Host, s.cfg.Port)

	if s.cfg.Port == 465 {
		return s.sendTLS(addr, ecfg.To, msg)
	}
	return s.sendSTARTTLS(addr, ecfg.To, msg)
}

func (s *EmailSender) sendTLS(addr string, to []string, msg []byte) error {
	tlsCfg := &tls.Config{ServerName: s.cfg.Host}
	conn, err := tls.Dial("tcp", addr, tlsCfg)
	if err != nil {
		return fmt.Errorf("tls dial: %w", err)
	}
	defer conn.Close()

	client, err := smtp.NewClient(conn, s.cfg.Host)
	if err != nil {
		return fmt.Errorf("smtp client: %w", err)
	}
	defer client.Quit()

	return s.authAndSend(client, to, msg)
}

func (s *EmailSender) sendSTARTTLS(addr string, to []string, msg []byte) error {
	conn, err := net.Dial("tcp", addr)
	if err != nil {
		return fmt.Errorf("dial: %w", err)
	}
	defer conn.Close()

	client, err := smtp.NewClient(conn, s.cfg.Host)
	if err != nil {
		return fmt.Errorf("smtp client: %w", err)
	}
	defer client.Quit()

	if ok, _ := client.Extension("STARTTLS"); ok {
		tlsCfg := &tls.Config{ServerName: s.cfg.Host}
		if err := client.StartTLS(tlsCfg); err != nil {
			return fmt.Errorf("starttls: %w", err)
		}
	}

	return s.authAndSend(client, to, msg)
}

func (s *EmailSender) authAndSend(client *smtp.Client, to []string, msg []byte) error {
	if s.cfg.User != "" {
		auth := smtp.PlainAuth("", s.cfg.User, s.cfg.Password, s.cfg.Host)
		if err := client.Auth(auth); err != nil {
			return fmt.Errorf("auth: %w", err)
		}
	}

	// MAIL FROM must be a bare address; display names like "Name <a@b.c>" are invalid here.
	fromAddr := extractEmailAddr(s.cfg.From)
	if err := client.Mail(fromAddr); err != nil {
		return fmt.Errorf("mail: %w", err)
	}
	for _, recipient := range to {
		if err := client.Rcpt(recipient); err != nil {
			return fmt.Errorf("rcpt %s: %w", recipient, err)
		}
	}
	w, err := client.Data()
	if err != nil {
		return fmt.Errorf("data: %w", err)
	}
	_, err = w.Write(msg)
	if err != nil {
		return fmt.Errorf("write: %w", err)
	}
	return w.Close()
}

func buildEmail(from string, to []string, subject, body string) []byte {
	var sb strings.Builder
	sb.WriteString(fmt.Sprintf("From: %s\r\n", from))
	sb.WriteString(fmt.Sprintf("To: %s\r\n", strings.Join(to, ", ")))
	sb.WriteString(fmt.Sprintf("Subject: %s\r\n", subject))
	sb.WriteString("MIME-Version: 1.0\r\n")
	sb.WriteString("Content-Type: text/plain; charset=utf-8\r\n")
	sb.WriteString("\r\n")
	sb.WriteString(body)
	return []byte(sb.String())
}

// extractEmailAddr returns the bare address from "Name <addr@host>" or the original string.
func extractEmailAddr(from string) string {
	start := strings.LastIndex(from, "<")
	end := strings.LastIndex(from, ">")
	if start >= 0 && end > start {
		return strings.TrimSpace(from[start+1 : end])
	}
	return strings.TrimSpace(from)
}