mira/backend/internal/mail/smtp.go

package mail

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

type SMTPConfig struct {
	Host     string
	Port     string
	User     string
	Password string
	From     string
	FromName string
}

type Sender struct {
	cfg SMTPConfig
}

func NewSender(cfg SMTPConfig) Sender {
	if strings.TrimSpace(cfg.Port) == "" {
		cfg.Port = "587"
	}
	return Sender{cfg: cfg}
}

func (s Sender) IsConfigured() bool {
	return strings.TrimSpace(s.cfg.Host) != "" &&
		strings.TrimSpace(s.cfg.Port) != "" &&
		strings.TrimSpace(s.cfg.From) != ""
}

func (s Sender) SendInvitation(to string, invitationURL string) error {
	subject := "Convite para acessar o Mira"
	textBody := "Voce foi convidado para acessar o Mira.\n\nCrie sua senha pelo link abaixo:\n" + invitationURL + "\n\nEste convite expira em 7 dias."
	htmlBody := `<p>Voce foi convidado para acessar o Mira.</p><p><a href="` + invitationURL + `">Criar minha senha</a></p><p>Este convite expira em 7 dias.</p>`

	return s.send(to, subject, textBody, htmlBody)
}

func (s Sender) send(to string, subject string, textBody string, htmlBody string) error {
	if !s.IsConfigured() {
		return nil
	}

	from := mail.Address{Name: strings.TrimSpace(s.cfg.FromName), Address: strings.TrimSpace(s.cfg.From)}
	recipient := mail.Address{Address: strings.TrimSpace(to)}
	boundary := "mira-mail-boundary"
	message := strings.Join([]string{
		"From: " + from.String(),
		"To: " + recipient.String(),
		"Subject: " + subject,
		"MIME-Version: 1.0",
		"Content-Type: multipart/alternative; boundary=\"" + boundary + "\"",
		"",
		"--" + boundary,
		"Content-Type: text/plain; charset=UTF-8",
		"",
		textBody,
		"--" + boundary,
		"Content-Type: text/html; charset=UTF-8",
		"",
		htmlBody,
		"--" + boundary + "--",
		"",
	}, "\r\n")

	host := strings.TrimSpace(s.cfg.Host)
	port := strings.TrimSpace(s.cfg.Port)
	addr := net.JoinHostPort(host, port)
	var auth smtp.Auth
	if strings.TrimSpace(s.cfg.User) != "" || strings.TrimSpace(s.cfg.Password) != "" {
		auth = smtp.PlainAuth("", strings.TrimSpace(s.cfg.User), strings.TrimSpace(s.cfg.Password), host)
	}

	if port == "465" {
		if err := sendMailTLS(addr, host, auth, from.Address, []string{recipient.Address}, []byte(message)); err != nil {
			return fmt.Errorf("send smtp email: %w", err)
		}
		return nil
	}

	if err := sendMailStartTLS(addr, host, auth, from.Address, []string{recipient.Address}, []byte(message)); err != nil {
		return fmt.Errorf("send smtp email: %w", err)
	}
	return nil
}

func sendMailStartTLS(addr string, host string, auth smtp.Auth, from string, to []string, message []byte) error {
	client, err := smtp.Dial(addr)
	if err != nil {
		return err
	}
	defer client.Quit()

	if ok, _ := client.Extension("STARTTLS"); ok {
		if err := client.StartTLS(&tls.Config{ServerName: host, MinVersion: tls.VersionTLS12}); err != nil {
			return err
		}
	}

	return sendMailWithClient(client, auth, from, to, message)
}

func sendMailTLS(addr string, host string, auth smtp.Auth, from string, to []string, message []byte) error {
	conn, err := tls.Dial("tcp", addr, &tls.Config{ServerName: host, MinVersion: tls.VersionTLS12})
	if err != nil {
		return err
	}

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

	return sendMailWithClient(client, auth, from, to, message)
}

func sendMailWithClient(client *smtp.Client, auth smtp.Auth, from string, to []string, message []byte) error {
	if auth != nil {
		if err := client.Auth(auth); err != nil {
			return err
		}
	}
	if err := client.Mail(from); err != nil {
		return err
	}
	for _, recipient := range to {
		if err := client.Rcpt(recipient); err != nil {
			return err
		}
	}

	writer, err := client.Data()
	if err != nil {
		return err
	}
	if _, err := writer.Write(message); err != nil {
		_ = writer.Close()
		return err
	}
	return writer.Close()
}