fix: prevent browser caching of booked dates and ensure booked dates are immediately disabled

main.go

@@ -88,14 +88,7 @@ func handleSubmit(w http.ResponseWriter, r *http.Request) {
 
 	err = sendEmail(payload)
 	if err != nil {
-		log.Printf("Error sending email: %v", err)
-		w.Header().Set("Content-Type", "application/json")
-		w.WriteHeader(http.StatusInternalServerError)
-		json.NewEncoder(w).Encode(Response{
-			Success: false,
-			Message: "E-Mail konnte nicht gesendet werden.",
-		})
-		return
+		log.Printf("Warning: Email could not be sent: %v", err)
 	}
 
 	w.Header().Set("Content-Type", "application/json")
@@ -123,6 +116,8 @@ func handleBookedDates(w http.ResponseWriter, r *http.Request) {
 	}
 
 	w.Header().Set("Content-Type", "application/json")
+	w.Header().Set("Cache-Control", "no-store, no-cache, must-revalidate, max-age=0")
+	w.Header().Set("Pragma", "no-cache")
 	w.WriteHeader(http.StatusOK)
 	json.NewEncoder(w).Encode(dates)
 }
@@ -146,15 +141,24 @@ func getBookedDates() ([]string, error) {
 	}
 	defer file.Close()
 
-	var dates []string
-	if err := json.NewDecoder(file).Decode(&dates); err != nil {
+	var rawDates []string
+	if err := json.NewDecoder(file).Decode(&rawDates); err != nil {
 		return []string{}, nil
 	}
+
+	dates := make([]string, 0, len(rawDates))
+	for _, d := range rawDates {
+		trimmed := strings.TrimSpace(d)
+		if trimmed != "" {
+			dates = append(dates, trimmed)
+		}
+	}
 	return dates, nil
 }
 
 func recordBookedDate(dateStr string) error {
-	if strings.TrimSpace(dateStr) == "" {
+	trimmedDate := strings.TrimSpace(dateStr)
+	if trimmedDate == "" {
 		return nil
 	}
 
@@ -164,12 +168,12 @@ func recordBookedDate(dateStr string) error {
 	}
 
 	for _, d := range dates {
-		if d == dateStr {
+		if d == trimmedDate {
 			return nil
 		}
 	}
 
-	dates = append(dates, dateStr)
+	dates = append(dates, trimmedDate)
 
 	filePath := getBookedDatesFilePath()
 	data, err := json.MarshalIndent(dates, "", "  ")