refactor: Reorganize SMTP2Shoutrrr code into separate files

server.go

@@ -0,0 +1,50 @@
+package smtp2shoutrrr
+
+import (
+	"context"
+	"fmt"
+	"log/slog"
+	"time"
+
+	"git.nakama.town/fmartingr/gotoolkit/model"
+	"github.com/emersion/go-smtp"
+)
+
+var _ model.Server = (*smtpServer)(nil)
+
+type smtpServer struct {
+	backend *smtp.Server
+	config  Config
+}
+
+func (s *smtpServer) IsEnabled() bool {
+	return true
+}
+
+func (s *smtpServer) Start(_ context.Context) error {
+	slog.Info("Started SMTP server", slog.String("addr", s.backend.Addr))
+	return s.backend.ListenAndServe()
+}
+
+func (s *smtpServer) Stop(ctx context.Context) error {
+	slog.Info("Stopping SMTP server")
+	return s.backend.Shutdown(ctx)
+}
+
+func NewSMTPServer(config *Config) model.Server {
+	be := &Backend{
+		config: config,
+	}
+
+	smtpBackend := smtp.NewServer(be)
+	smtpBackend.Addr = fmt.Sprintf(":%d", config.Port)
+	smtpBackend.WriteTimeout = 10 * time.Second
+	smtpBackend.ReadTimeout = 10 * time.Second
+	smtpBackend.MaxMessageBytes = 1024 * 1024
+	smtpBackend.MaxRecipients = 50
+	smtpBackend.AllowInsecureAuth = true
+
+	return &smtpServer{
+		backend: smtpBackend,
+	}
+}