refactor: Reorganize SMTP2Shoutrrr code into separate files

backend.go

@@ -0,0 +1,116 @@
+package smtp2shoutrrr
+
+import (
+	"fmt"
+	"io"
+	"log/slog"
+	"net/mail"
+	"net/url"
+	"slices"
+	"strings"
+
+	"github.com/containrrr/shoutrrr"
+	"github.com/emersion/go-sasl"
+	"github.com/emersion/go-smtp"
+)
+
+type Backend struct {
+	config *Config
+}
+
+func (bkd *Backend) NewSession(c *smtp.Conn) (smtp.Session, error) {
+	return &Session{
+		forwarderFunc: bkd.forwardEmail,
+		config:        bkd.config,
+	}, nil
+}
+
+func (bkd *Backend) forwardEmail(email ReceivedEmail) error {
+	slog.Info("forwading message", slog.String("to", strings.Join(email.Recipients, ",")))
+
+	for _, r := range bkd.config.Recipients {
+		for _, a := range email.Recipients {
+			if slices.Contains(r.Addresses, a) {
+				urlParams := url.Values{
+					"title": {email.Msg.Header.Get("Subject")},
+				}
+
+				destinationURL := r.GetTargetURL()
+				destinationURL.RawQuery = urlParams.Encode()
+
+				body, err := email.Body()
+				if err != nil {
+					slog.Error("Error getting email body", slog.String("err", err.Error()))
+					continue
+				}
+
+				if err := shoutrrr.Send(destinationURL.String(), body); err != nil {
+					slog.Error("Error sending message", slog.String("err", err.Error()))
+					continue
+				}
+
+				break
+			}
+		}
+	}
+
+	return nil
+}
+
+type Session struct {
+	addresses []string
+	body      string
+
+	config *Config
+
+	forwarderFunc func(ReceivedEmail) error
+}
+
+func (s *Session) AuthMechanisms() []string {
+	return []string{sasl.Plain}
+}
+
+func (s *Session) Auth(mech string) (sasl.Server, error) {
+	return sasl.NewPlainServer(func(identity, username, password string) error {
+		if username != s.config.Username && password != s.config.Password {
+			return fmt.Errorf("invalid credentials")
+		}
+		return nil
+	}), nil
+}
+
+func (s *Session) Mail(from string, opts *smtp.MailOptions) error {
+	slog.Debug("Mail from", slog.String("from", from))
+	return nil
+}
+
+func (s *Session) Rcpt(to string, opts *smtp.RcptOptions) error {
+	slog.Debug("Rcpt to", slog.String("to", to))
+	s.addresses = append(s.addresses, to)
+	return nil
+}
+
+func (s *Session) Data(r io.Reader) error {
+	msg, err := mail.ReadMessage(r)
+	if err != nil {
+		slog.Error("Error reading data", slog.String("err", err.Error()))
+		return fmt.Errorf("Error reading data: %w", err)
+	}
+
+	slog.Info("Received email", slog.String("destination", strings.Join(s.addresses, ",")))
+
+	if err := s.forwarderFunc(ReceivedEmail{
+		Recipients: s.addresses,
+		Msg:        msg,
+	}); err != nil {
+		slog.Error("Error forwarding email", slog.String("err", err.Error()))
+	}
+
+	return nil
+}
+
+func (s *Session) Reset() {}
+
+func (s *Session) Logout() error {
+	return nil
+}