Implement GetCostFromDuration() in terms of private_GetCostFromDuration()

using a ticket as return value.

library/src/calculator_functions.cpp

@@ -3,6 +3,7 @@
 #include "utilities.h"
 #include "tariff_log.h"
 #include "tariff_time_range.h"
+#include "ticket.h"
 
 #include <sstream>
 #include <algorithm>
@@ -404,9 +405,18 @@ double Calculator::GetCostFromDuration(Configuration* cfg,
         return GetCostFromDuration(cfg, start_datetime, end_datetime);
     }
 
-    return private_GetCostFromDuration(cfg, start_datetime,
-                                       end_datetime, durationMinutes,
-                                       nextDay, prepaid);
+    QDateTime start = start_datetime;
+
+    Ticket t = private_GetCostFromDuration(cfg, start,
+                                           end_datetime, durationMinutes,
+                                           nextDay, prepaid);
+    if (t) {
+        qCritical().noquote() << t;
+
+        return t.getPrice();
+    }
+
+    return -1;
 }
 
 int Calculator::getMinimalParkingTime(Configuration const *cfg, PaymentMethod methodId) {