wip: invoice reference generation

internal/lib/utils.go

@@ -5,6 +5,7 @@ import (
 	"net/http"
 	"os"
 	"path/filepath"
+	"time"
 
 	"github.com/google/uuid"
 	"github.com/gorilla/sessions"
@@ -267,3 +268,9 @@ func GenerateInvoice(invoice types.Invoice, user types.User, client types.Client
 
 	return invoicePath, nil
 }
+
+func GenerateInvoiceReference(invoiceNumber uint32) string {
+	year, _, _ := time.Now().Date()
+
+	return fmt.Sprintf("INV/%d/%05d", year, invoiceNumber)
+}