func opt pattern

internal/server/server.go

@@ -29,16 +29,41 @@ type Server struct {
 	addr   string
 }
 
-func New(fs *embed.FS, bs *booking.Service, ps *pdf.PdfService, hc *config.Host) *Server {
+type options struct {
+	port *int
+}
+
+type Option func(*options) error
+
+func WithPort(port int) Option {
+	return func(o *options) error {
+		if port <= 0 {
+			return errors.New("port should be positive")
+		}
+		o.port = &port
+		return nil
+	}
+}
+
+func New(fs *embed.FS, bs *booking.Service, ps *pdf.PdfService, hc *config.Host, opts ...Option) (*Server, error) {
+	option := new(options)
+	for _, opt := range opts {
+		err := opt(option)
+		if err != nil {
+			return nil, err
+		}
+	}
+
 	s := &Server{
 		Router: NewRouter(*fs),
 		bs:     bs,
 		ps:     ps,
 		hc:     hc,
-		addr:   fmt.Sprintf("0.0.0.0:%s", os.Getenv("PORT")),
+		addr:   fmt.Sprintf("0.0.0.0:%d", *option.port),
 	}
+
 	s.MountHandlers()
-	return s
+	return s, nil
 }
 
 func (s Server) Start() {

main.go

@@ -4,6 +4,7 @@ import (
 	"embed"
 	"log"
 	"os"
+	"strconv"
 
 	"github.com/joho/godotenv"
 	"gorm.io/driver/postgres"
@@ -43,5 +44,14 @@ func main() {
 		log.Fatal(err)
 	}
 
-	server.New(&static, booking.NewService(db), ps, config.NewHost()).Start()
+	p := os.Getenv("PORT")
+	port, err := strconv.Atoi(p)
+	if err != nil {
+		log.Fatal(err)
+	}
+	srv, err := server.New(&static, booking.NewService(db), ps, config.NewHost(), server.WithPort(port))
+	if err != nil {
+		log.Fatal(err)
+	}
+	srv.Start()
 }