Add compute_next_timestep() computing timesteps if PaymentMethod = Steps.

Add additional code for computing time steps dynamically if PaymentMethod = Linear.

library/src/calculate_price.cpp

@@ -2,6 +2,7 @@
 #include "configuration.h"
 #include "calculator_functions.h"
 #include "payment_option.h"
+#include "utilities.h"
 
 #include <QFile>
 #include <QFileInfo>
@@ -92,6 +93,77 @@ void CALCULATE_LIBRARY_API free_tariff(parking_tariff_t *tariff) {
     }
 }
 
+//
+// UpDown 1 -> up; 0 -> down
+int CALCULATE_LIBRARY_API compute_next_timestep(parking_tariff_t *tariff, int currentTimeMinutes, int UpDown)
+{
+    // use tariff with structure as for instance Schnau, Koenigsee:
+    // without given YearPeriod, SpecialDays and SpecialDaysWorktime
+    if (tariff->YearPeriod.size() == 0
+        && tariff->SpecialDays.size() == 0
+        && tariff->SpecialDaysWorktime.size() == 0)
+    {
+        static const QList<int> stepList = calculator.GetTimeSteps(tariff);
+
+        int currentStepIndex = stepList.indexOf(currentTimeMinutes);
+
+        if (currentStepIndex == -1) {
+            qCritical() << "compute_next_timestep() *NO STEP* for currentTimeMinutes (" << currentTimeMinutes << ")";
+            return  currentTimeMinutes;
+        }
+
+        if (UpDown == 1) { // UP
+            if (stepList[currentStepIndex] == stepList.last()) {
+                qCritical() << "compute_next_timestep() *NO NEXT STEP* for currentTimeMinutes (" << currentTimeMinutes << ")";
+                return  currentTimeMinutes;
+            }
+            else {
+                return stepList[currentStepIndex + 1];
+            }
+        }
+        if (UpDown == 0) { // DOWN
+            if (stepList[currentStepIndex] == stepList.first()) {
+                qCritical() << "compute_next_timestep() *NO PREVIOUS STEP* for currentTimeMinutes (" << currentTimeMinutes << ")";
+                return  currentTimeMinutes;
+            }
+            else {
+                return stepList[currentStepIndex - 1];
+            }
+        }
+    } else {
+        Configuration const *cfg = tariff;
+
+        // currentTimeMinutes is the number of minutes actually used. This
+        // value is an offset from the start time and cannot be used as a
+        // QDateTime.
+
+        qCritical() << "compute_next_timestep() currentTimeMinutes:" << currentTimeMinutes;
+
+        // compute payment method id (e.g. Linear=3, Steps=4)
+        PaymentMethod paymentMethodId = Utilities::getPaymentMethodId(cfg);
+        qCritical() << "   compute_next_timestep() paymentMethodId:" << paymentMethodId;
+
+        // get minimal and maximal parking times
+        int const minParkingTime = Utilities::getMinimalParkingTime(cfg, paymentMethodId);
+        int const maxParkingTime = Utilities::getMaximalParkingTime(cfg, paymentMethodId);
+
+        qCritical() << "    compute_next_timestep() maxParkingTime:" << paymentMethodId;
+        qCritical() << "    compute_next_timestep() minParkingTime:" << paymentMethodId;
+
+        // use the first (i.e. main duration step contained in the tariff json-file)
+        int firstDurationStep = Utilities::getFirstDurationStep(cfg, paymentMethodId);
+        qCritical() << " compute_next_timestep() firstDurationStep:" << paymentMethodId;
+
+        int nextTimeStep = currentTimeMinutes + firstDurationStep;
+        if (currentTimeMinutes >= minParkingTime && nextTimeStep <= maxParkingTime) {
+            qCritical() << "  compute_next_timestep() nextTimeStep:" << nextTimeStep;
+            return nextTimeStep;
+        }
+    }
+
+    qCritical() << "compute_next_timestep() *CAN NOT COMPUTE* for currentTimeMinutes (" << currentTimeMinutes << ")";
+    return  currentTimeMinutes;
+}
 
 // this is currently not used
 CalcState CALCULATE_LIBRARY_API compute_price_for_parking_ticket(