smtp2shoutrrr/backend.go

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) sendNotifications(recipient ConfigRecipient, email ReceivedEmail) error {
	// Get all target URLs (handles merging and caching)
	targetURLs := recipient.GetTargetURLs()

	if len(targetURLs) == 0 {
		slog.Warn("no valid targets provided for recipient",
			slog.String("recipient", strings.Join(recipient.Addresses, ",")))
		return nil
	}

	// Prepare email body once (reuse for all targets)
	body, err := email.Body()
	if err != nil {
		slog.Error("Error getting email body", slog.String("err", err.Error()))
		return fmt.Errorf("failed to get email body: %w", err)
	}

	slog.Debug("Prepared email body",
		slog.Int("body_length", len(body)),
		slog.String("subject", email.Msg.Header.Get("Subject")),
		slog.String("content_type", email.Msg.Header.Get("Content-Type")))

	urlParams := url.Values{
		"title": {email.Msg.Header.Get("Subject")},
	}

	// Send to all targets, collect errors
	var errs []error
	for i, targetURL := range targetURLs {
		// Clone URL to avoid mutation
		destinationURL := *targetURL

		// Merge new params with existing query params
		existingParams := destinationURL.Query()
		for key, values := range urlParams {
			for _, value := range values {
				existingParams.Add(key, value)
			}
		}
		destinationURL.RawQuery = existingParams.Encode()

		if err := shoutrrr.Send(destinationURL.String(), body); err != nil {
			slog.Error("Error sending message to target",
				slog.Int("target_index", i),
				slog.String("target", targetURL.Host),
				slog.String("err", err.Error()))
			errs = append(errs, fmt.Errorf("target %d: %w", i, err))
			// Continue to next target even if this one fails
		} else {
			slog.Info("Successfully sent notification",
				slog.String("target", targetURL.Host),
				slog.String("recipient", strings.Join(recipient.Addresses, ",")))
		}
	}

	// Return aggregated error if any failed
	if len(errs) > 0 {
		return fmt.Errorf("failed to send to %d/%d targets: %v",
			len(errs), len(targetURLs), errs)
	}

	return nil
}

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, ",")))

	// Try to match configured recipients first
	matched := false
	for _, r := range bkd.config.Recipients {
		for _, a := range email.Recipients {
			if slices.Contains(r.Addresses, a) {
				if err := bkd.sendNotifications(r, email); err != nil {
					return err
				}
				matched = true
				break
			}
		}
		if matched {
			break
		}
	}

	// If no recipient matched and catch-all is configured, use it
	if !matched && bkd.config.CatchAll != nil {
		slog.Info("using catch-all recipient for unmatched email")
		if err := bkd.sendNotifications(*bkd.config.CatchAll, email); err != nil {
			return err
		}
	}

	return nil
}

type Session struct {
	addresses []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
}