diff --git a/Calculator/main.cpp b/Calculator/main.cpp
new file mode 100644
index 0000000..afa649b
--- /dev/null
+++ b/Calculator/main.cpp
@@ -0,0 +1,10 @@
+#include <QDebug>
+
+#include "calculator_c_interface_lib.h"
+
+int main() {
+
+    qCritical() << "initTariffEditor" << initTariffEditor();
+
+    return 0;
+}
diff --git a/CalculatorCInterface/CalculatorCInterface.pro b/CalculatorCInterface/CalculatorCInterface.pro
new file mode 100644
index 0000000..c7943c0
--- /dev/null
+++ b/CalculatorCInterface/CalculatorCInterface.pro
@@ -0,0 +1,29 @@
+QT -= gui
+
+TEMPLATE = lib
+DEFINES += CACULATOR_C_INTERFACE_LIBRARY
+
+# INCLUDEPATH+=$$_PRO_FILE_PWD_/../Utilities/
+
+
+CONFIG += c++17
+QMAKE_CXX=x86_64-w64-mingw32-g++
+
+# You can make your code fail to compile if it uses deprecated APIs.
+# In order to do so, uncomment the following line.
+#DEFINES += QT_DISABLE_DEPRECATED_BEFORE=0x060000    # disables all the APIs deprecated before Qt 6.0.0
+
+SOURCES += \
+    calculator_c_interface_lib.cpp \
+    tariff_editor.cpp
+
+HEADERS += \
+    calculator_c_interface_lib.h \
+    calculator_c_interface_lib_global.h
+    tariff_editor.h
+
+# Default rules for deployment.
+unix {
+    target.path = /usr/lib
+}
+!isEmpty(target.path): INSTALLS += target
diff --git a/CalculatorCInterface/calculator_c_interface_lib.cpp b/CalculatorCInterface/calculator_c_interface_lib.cpp
new file mode 100644
index 0000000..ad4ca3e
--- /dev/null
+++ b/CalculatorCInterface/calculator_c_interface_lib.cpp
@@ -0,0 +1,18 @@
+#include "calculator_c_interface_lib.h"
+#include "tariff_editor.h"
+
+
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+
+bool CACULATOR_C_INTERFACE_LIB_EXPORT initTariffEditor() {
+    TariffEditor editor;
+    return true;
+}
+
+#ifdef __cplusplus
+}
+#endif
diff --git a/CalculatorCInterface/calculator_c_interface_lib.h b/CalculatorCInterface/calculator_c_interface_lib.h
new file mode 100644
index 0000000..85fd4e7
--- /dev/null
+++ b/CalculatorCInterface/calculator_c_interface_lib.h
@@ -0,0 +1,20 @@
+#ifndef CALCULATOR_C_INTERFACE_LIB_H_INCLUDED
+#define CALCULATOR_C_INTERFACE_LIB_H_INCLUDED
+
+#include "calculator_c_interface_lib_global.h"
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+bool CACULATOR_C_INTERFACE_LIB_EXPORT initTariffEditor();
+
+#ifdef __cplusplus
+}
+#endif
+//{
+//public:
+//    Testlib();
+//};
+
+#endif // CALCULATOR_C_INTERFACE_LIB_H_INCLUDED
diff --git a/CalculatorCInterface/calculator_c_interface_lib_global.h b/CalculatorCInterface/calculator_c_interface_lib_global.h
new file mode 100644
index 0000000..c5150b7
--- /dev/null
+++ b/CalculatorCInterface/calculator_c_interface_lib_global.h
@@ -0,0 +1,12 @@
+#ifndef CALCULATOR_C_INTERFACE_GLOBAL_H
+#define CALCULATOR_C_INTERFACE_GLOBAL_H
+
+#include <QtCore/qglobal.h>
+
+#if defined(CACULATOR_C_INTERFACE_LIBRARY)
+    #define CACULATOR_C_INTERFACE_LIB_EXPORT Q_DECL_EXPORT
+#else
+    #define CACULATOR_C_INTERFACE_LIB_EXPORT Q_DECL_IMPORT
+#endif
+
+#endif // CALCULATOR_C_INTERFACE_GLOBAL_H
diff --git a/CalculatorCInterface/tariff_editor.cpp b/CalculatorCInterface/tariff_editor.cpp
new file mode 100644
index 0000000..c996eeb
--- /dev/null
+++ b/CalculatorCInterface/tariff_editor.cpp
@@ -0,0 +1,423 @@
+#include "tariff_editor.h"
+
+#include <QDebug>
+#include <QFile>
+#include <QTextStream>
+#include <QDateTime>
+#include <QJsonDocument>
+#include <QJsonParseError>
+#include <QJsonArray>
+#include <QJsonObject>
+#include <QJsonValue>
+
+QByteArray TariffEditor::readJson(QString const &filename) {
+    QFile f(filename);
+    if (f.exists()) {
+        if (f.open(QFile::ReadOnly | QFile::Text)) {
+            QTextStream in(&f);
+            return in.readAll().toUtf8();
+        } else {
+            qCritical() << filename << "not readable";
+        }
+    } else {
+        qCritical() << filename << "does not exist";
+    }
+
+    return QByteArray();
+}
+
+
+TariffEditor::TariffEditor() {
+
+    // QByteArray ba = readJson("/opt/ptu5/opt/ATBTariffCalculator/Utilities/tariff.template.json");
+
+    //QJsonParseError pe;
+    //m_jsonDoc = QJsonDocument::fromJson(ba, &pe);
+    //if (pe.error == QJsonParseError::NoError) {
+    //    qCritical().noquote() << m_jsonDoc.toJson(QJsonDocument::JsonFormat::Indented);
+    //} else {
+    //    qCritical() << __func__ << pe.errorString();
+    //
+    //}
+
+    m_a = QJsonArray();
+    createJsonValue("Project", "Szeged");
+    createJsonValue("Version", "1.0.0");
+    createJsonValue("Date", "01.01.1970");
+    createJsonValue("Committer", "");
+    createJsonValue("Info", "");
+    createJsonValue("Products");
+    createJsonValue("Accuracy");
+    createJsonValue("Type");
+    createJsonValue("Price");
+    createJsonValue("Config");
+    createJsonValue("TimeRanges");
+    createJsonValue("Periods");
+    createJsonValue("DayConfigs");
+    createJsonValue("Days");
+
+    m_jsonDoc.setArray(m_a);
+    qCritical().noquote() << m_jsonDoc.toJson(QJsonDocument::JsonFormat::Indented);
+}
+
+void TariffEditor::createJsonValue(QString const &key, QString const &value) {
+
+    if ((key.compare("Project", Qt::CaseInsensitive) == 0)
+     || (key.compare("Version", Qt::CaseInsensitive) == 0)
+     || (key.compare("Date", Qt::CaseInsensitive) == 0)
+     || (key.compare("Committer", Qt::CaseInsensitive) == 0)
+     || (key.compare("Info", Qt::CaseInsensitive) == 0)) {
+        m_a.push_back(QJsonValue({QPair(key, QJsonValue(value))}));
+    } else
+    if (key.compare("Accuracy", Qt::CaseInsensitive) == 0) {
+        QJsonObject o({
+            QPair(QString("accuracy_id"), QJsonValue(1)),
+            QPair(QString("accuracy_label"), QJsonValue(QString("computation-to-the-minute"))),
+            QPair(QString("accuracy_value"), QJsonValue(1)),
+            QPair(QString("comment"), QJsonValue(QString("accuracy of tariff computation is individual minutes")))});
+
+       m_a.push_back(QJsonObject({QPair(key, QJsonValue(o))}));
+    } else
+    if (key.compare("Type", Qt::CaseInsensitive) == 0) {
+        QJsonObject o({
+            QPair(QString("type_id"), QJsonValue(1)),
+            QPair(QString("type_label"), QJsonValue(QString("uniform-minutes"))),
+            QPair(QString("comment"), QJsonValue(QString("same price for all minutes")))});
+
+        m_a.push_back(QJsonObject({QPair(key, QJsonValue(o))}));
+    } else
+    if (key.compare("Price", Qt::CaseInsensitive) == 0) {
+        QJsonObject o1({
+            QPair(QString("price_id"), QJsonValue(1)),
+            QPair(QString("price"), QJsonValue(165)),
+            QPair(QString("editable"), QJsonValue(true)),
+            QPair(QString("comment"), QJsonValue(QString("price per hour as provided by customer")))});
+
+        QJsonObject o2({
+            QPair(QString("price_id"), QJsonValue(2)),
+            QPair(QString("price"), QJsonValue(990)),
+            QPair(QString("editable"), QJsonValue(true)),
+            QPair(QString("comment"), QJsonValue(QString("price for dayticket as provided by customer")))});
+
+        QJsonArray a;
+        a.push_back(o1);
+        a.push_back(o2);
+
+        m_a.push_back(QJsonObject({QPair(key, QJsonValue(a))}));
+    } else
+    if (key.compare("Config", Qt::CaseInsensitive) == 0) {
+        QJsonObject o1({
+            QPair(QString("value"), QJsonValue(15)),
+            QPair(QString("editable"), QJsonValue(true)),
+            QPair(QString("comment"), QJsonValue(QString("minimal parking time in minutes (net)")))});
+
+        QJsonObject o2({
+            QPair(QString("value"), QJsonValue(360)),
+            QPair(QString("editable"), QJsonValue(true)),
+            QPair(QString("comment"), QJsonValue(QString("maximal parking time in minutes (net)")))});
+
+        QJsonObject o3({
+            QPair(QString("value"), QJsonValue(1)),
+            QPair(QString("comment"), QJsonValue(QString("price-id of customer entered price (for hour) expressed in minimal time: 15*(165/60) = 41.25")))});
+
+        QJsonObject o4({
+            QPair(QString("value"), QJsonValue(1)),
+            QPair(QString("comment"), QJsonValue(QString("price-id of customer entered price (for hour) expressed in maximal time: 360*(165/60) = 990")))});
+
+        QJsonObject o5({
+            QPair(QString("comment"), QJsonValue(QString("general tariff config"))),
+            QPair(QString("config_id"), QJsonValue(1)),
+            QPair(QString("config_label"), QJsonValue("Tariff Config 1")),
+            QPair(QString("config_tariff_accuracy"), QJsonValue(1)),
+            QPair(QString("config_tariff_type"), QJsonValue(1)),
+            QPair(QString("config_carry_over"), QJsonValue(true)),
+            QPair(QString("config_prepaid"), QJsonValue(true)),
+            QPair(QString("MinimalTime"), QJsonValue(o1)),
+            QPair(QString("MaximalTime"), QJsonValue(o2)),
+            QPair(QString("MinimalPrice"), QJsonValue(o3)),
+            QPair(QString("MinimalPrice"), QJsonValue(o4))});
+
+        m_a.push_back(QJsonObject({QPair(key, QJsonValue(o5))}));
+    } else
+    if (key.compare("Products", Qt::CaseInsensitive) == 0) {
+        QJsonObject o1({
+            QPair(QString("product_id"), QJsonValue(1)),
+            QPair(QString("product_price_id"), QJsonValue(1)),
+            QPair(QString("product_label"), QJsonValue(QString("SHORT_TIME_PARKING")))});
+
+        QJsonObject o2({
+            QPair(QString("product_id"), QJsonValue(2)),
+            QPair(QString("product_price_id"), QJsonValue(2)),
+            QPair(QString("product_time_ranges"), QJsonArray({QJsonValue(100001)})),
+            QPair(QString("product_label"), QJsonValue(QString("DAY_TICKET")))});
+
+        QJsonArray a;
+        a.push_back(o1);
+        a.push_back(o2);
+
+        m_a.push_back(QJsonObject({QPair(key, QJsonValue(a))}));
+    } else
+    if (key.compare("TimeRanges", Qt::CaseInsensitive) == 0) {
+        QJsonObject o1({
+            QPair(QString("range_id"), QJsonValue(1)),
+            QPair(QString("range_price_id"), QJsonValue(0)),
+            QPair(QString("range_start"), QJsonValue(QString("00:00:00"))),
+            QPair(QString("range_end"), QJsonValue(QString("00:00:00"))),
+            QPair(QString("comment"), QJsonValue(QString("[ 00:00-00:00 [ = [ 00:00-24:00 [")))});
+
+        QJsonObject o2({
+            QPair(QString("range_id"), QJsonValue(1)),
+            QPair(QString("range_price_id"), QJsonValue(1)),
+            QPair(QString("range_start"), QJsonValue(QString("00:00:00"))),
+            QPair(QString("range_end"), QJsonValue(QString("08:00:00"))),
+            QPair(QString("comment"), QJsonValue(QString("[ 00:00-08:00 [")))});
+
+        QJsonObject o3({
+            QPair(QString("range_id"), QJsonValue(1)),
+            QPair(QString("range_price_id"), QJsonValue(2)),
+            QPair(QString("range_start"), QJsonValue(QString("18:00:00"))),
+            QPair(QString("range_end"), QJsonValue(QString("00:00:00"))),
+            QPair(QString("comment"), QJsonValue(QString("[ 18:00-00:00 [")))});
+
+        QJsonObject o4({
+            QPair(QString("range_id"), QJsonValue(1)),
+            QPair(QString("range_price_id"), QJsonValue(3)),
+            QPair(QString("range_start"), QJsonValue(QString("12:00:00"))),
+            QPair(QString("range_end"), QJsonValue(QString("00:00:00"))),
+            QPair(QString("comment"), QJsonValue(QString("[ 12:00-00:00 [")))});
+
+        QJsonArray a;
+        a.push_back(o1);
+        a.push_back(o2);
+        a.push_back(o3);
+        a.push_back(o4);
+
+        QTime const t(8,0,0);
+        QJsonArray b;
+        for (int i=0; i<600; ++i) {
+
+            QTime const &start = t.addSecs(i*60);
+            QTime const &end = t.addSecs((i+1)*60);
+
+            QJsonObject o({
+                QPair(QString("range_id"), QJsonValue(i)),
+                QPair(QString("range_price_id"), QJsonValue(0)),
+                QPair(QString("range_start"), QJsonValue(start.toString(Qt::ISODate))),
+                QPair(QString("range_end"), QJsonValue(end.toString(Qt::ISODate)))});
+
+            b.push_back(o);
+        }
+
+        a.push_back(b);
+        m_a.push_back(QJsonObject({QPair(key, QJsonValue(a))}));
+    } else
+    if (key.compare("Periods", Qt::CaseInsensitive) == 0) {
+        QJsonObject o1({
+            QPair(QString("period_id"), QJsonValue(1)),
+            QPair(QString("period_label"), QJsonValue("1st quarter")),
+            QPair(QString("period_from"), QJsonValue(QString("1970-01-01"))),
+            QPair(QString("period_until"), QJsonValue(QString("1970-03-31")))});
+
+        QJsonObject o2({
+            QPair(QString("period_id"), QJsonValue(2)),
+            QPair(QString("period_label"), QJsonValue("2nd quarter")),
+            QPair(QString("period_from"), QJsonValue(QString("1970-04-01"))),
+            QPair(QString("period_until"), QJsonValue(QString("1970-06-30")))});
+
+        QJsonObject o3({
+            QPair(QString("period_id"), QJsonValue(3)),
+            QPair(QString("period_label"), QJsonValue("3rd quarter")),
+            QPair(QString("period_from"), QJsonValue(QString("1970-07-01"))),
+            QPair(QString("period_until"), QJsonValue(QString("1970-09-30")))});
+
+        QJsonObject o4({
+            QPair(QString("period_id"), QJsonValue(4)),
+            QPair(QString("period_label"), QJsonValue("4th quarter")),
+            QPair(QString("period_from"), QJsonValue(QString("1970-10-01"))),
+            QPair(QString("period_until"), QJsonValue(QString("1970-12-31")))});
+
+        QJsonObject o5({
+            QPair(QString("period_id"), QJsonValue(5)),
+            QPair(QString("period_label"), QJsonValue("1st half-year")),
+            QPair(QString("period_from"), QJsonValue(QString("1970-01-01"))),
+            QPair(QString("period_until"), QJsonValue(QString("1970-06-30")))});
+
+        QJsonObject o6({
+            QPair(QString("period_id"), QJsonValue(6)),
+            QPair(QString("period_label"), QJsonValue("2nd half-year")),
+            QPair(QString("period_from"), QJsonValue(QString("1970-07-01"))),
+            QPair(QString("period_until"), QJsonValue(QString("1970-12-31")))});
+
+        QJsonArray a;
+        a.push_back(o1);
+        a.push_back(o2);
+        a.push_back(o3);
+        a.push_back(o4);
+        a.push_back(o5);
+        a.push_back(o6);
+
+        m_a.push_back(QJsonObject({QPair(key, QJsonValue(a))}));
+    } else
+    if (key.compare("DayConfigs", Qt::CaseInsensitive) == 0) {
+
+        QJsonArray b;
+        b.push_back(QJsonValue(100002));
+        for (int i=0; i<600; ++i) {
+            b.push_back(QJsonValue(i));
+        }
+        b.push_back(QJsonValue(100003));
+
+        QJsonArray c;
+        c.push_back(QJsonValue(100001));
+
+        QJsonObject o1({
+            QPair(QString("day_config_id"), QJsonValue(1)),
+            QPair(QString("day_config_range"), QJsonValue(6)),
+            QPair(QString("day_config_product_ids"), QJsonArray({QJsonValue(0), QJsonValue(1)})),
+            QPair(QString("day_config_short_time_parking"), b),
+            QPair(QString("day_config_day_ticket"), c)});
+
+        QJsonObject o2({QPair(QString("DayConfig_1"), QJsonValue(o1))});
+
+        QJsonObject o3({
+            QPair(QString("day_config_id"), QJsonValue(2)),
+            QPair(QString("day_config_range"), QJsonValue(6)),
+            QPair(QString("day_config_product_ids"), QJsonArray({QJsonValue(1)})),
+            QPair(QString("day_config_day_ticket"), c)});
+
+        QJsonObject o4({QPair(QString("DayConfig_2"), QJsonValue(o3))});
+
+        QJsonArray a;
+        a.push_back(o2);
+        a.push_back(o4);
+
+        m_a.push_back(QJsonObject({QPair(key, QJsonValue(a))}));
+    } else
+    if (key.compare("Days", Qt::CaseInsensitive) == 0) {
+        QJsonArray b;
+        for (int i=1; i < 8; ++i) {
+            QJsonObject o1({
+                QPair(QString("day_id"), QJsonValue(1)),
+                QPair(QString("day_config_id"), QJsonValue(0))});
+
+            switch(i) {
+            case Qt::Monday: {
+                QJsonObject o2({QPair(QString("Mon"), QJsonValue(o1))});
+                b.push_back(o2);
+            } break;
+            case Qt::Tuesday: {
+                QJsonObject o2({QPair(QString("Tue"), QJsonValue(o1))});
+                b.push_back(o2);
+            } break;
+            case Qt::Wednesday: {
+                QJsonObject o2({QPair(QString("Wed"), QJsonValue(o1))});
+                b.push_back(o2);
+            } break;
+            case Qt::Thursday: {
+                QJsonObject o2({QPair(QString("Thu"), QJsonValue(o1))});
+                b.push_back(o2);
+            } break;
+            case Qt::Friday: {
+                QJsonObject o2({QPair(QString("Fri"), QJsonValue(o1))});
+                b.push_back(o2);
+            } break;
+            case Qt::Saturday: {
+                QJsonObject o2({QPair(QString("Sat"), QJsonValue(o1))});
+                b.push_back(o2);
+            } break;
+            case Qt::Sunday: {
+                QJsonObject o2({QPair(QString("Sun"), QJsonValue(o1))});
+                b.push_back(o2);
+            } break;
+            }
+        }
+
+
+        QJsonArray c;
+        QJsonObject o1({
+            QPair(QString("day_id"), QJsonValue(1)),
+            QPair(QString("day_config_id"), QJsonValue(1)),
+            QPair(QString("day_date"), QJsonValue(QString("2024-12-25"))),
+            QPair(QString("day_movable"), QJsonValue(false))});
+        QJsonObject o2({
+            QPair(QString("day_id"), QJsonValue(2)),
+            QPair(QString("day_config_id"), QJsonValue(1)),
+            QPair(QString("day_date"), QJsonValue(QString("2024-12-26"))),
+            QPair(QString("day_movable"), QJsonValue(false))});
+        c.push_back(o1);
+        c.push_back(o2);
+
+        QJsonObject o3({QPair(QString("Weekdays"), b),
+                        QPair(QString("Holidays"), c)});
+
+        //"Christmas_1st_day": {
+        //    "day_id": 8,
+        //    "day_config_id": 1,
+        //    "day_date": "2024-12-25",
+        //    "day_moveable": false
+        //},
+        //"Christmas_2nd_day": {
+        //    "day_id": 9,
+        //    "day_config_id": 1,
+        //    "day_date": "2024-12-26",
+        //    "day_moveable": false
+        //}
+
+        m_a.push_back(QJsonObject({QPair(key, QJsonValue(o3))}));
+    }
+
+#if 0
+
+    "TariffDays": [
+        "Mon": {
+            "day_id": 1,
+            "day_config_id": 0
+        },
+        "Tue": {
+            "day_id": 2,
+            "day_config_id": 0
+        },
+        "Wed": {
+            "day_id": 3,
+            "day_config_id": 0
+        },
+        "Thu": {
+            "day_id": 4,
+            "day_config_id": 0
+        },
+        "Fri": {
+            "day_id": 5,
+            "day_config_id": 0
+        },
+        "Sat": {
+            "day_id": 6,
+            "day_config_id": 0
+        },
+        "Sun": {
+            "day_id": 7,
+            "day_config_id": 0
+        },
+        "Christmas_1st_day": {
+            "day_id": 8,
+            "day_config_id": 1,
+            "day_date": "2024-12-25",
+            "day_moveable": false
+        },
+        "Christmas_2nd_day": {
+            "day_id": 9,
+            "day_config_id": 1,
+            "day_date": "2024-12-26",
+            "day_moveable": false
+        }
+    // usw. die anderen Feiertage un
+
+    "DayConfig_1": {
+        "day_config_id": 0,
+        "day_config_date_range": 6,
+    "comment_1": "day config is valid for the whole year",
+        "day_config_product_ids": [0, 1],
+    "comment_2": "short-time-parking or day-ticket on this day",
+
+#endif
+
+}
diff --git a/CalculatorCInterface/tariff_editor.h b/CalculatorCInterface/tariff_editor.h
new file mode 100644
index 0000000..02c909f
--- /dev/null
+++ b/CalculatorCInterface/tariff_editor.h
@@ -0,0 +1,20 @@
+#ifndef TARIFF_EDITOR_H_INCLUDED
+#define TARIFF_EDITOR_H_INCLUDED
+
+#include <QByteArray>
+#include <QString>
+
+#include <QJsonDocument>
+#include <QJsonArray>
+
+class TariffEditor {
+    QJsonArray m_a;
+    QJsonDocument m_jsonDoc;
+    void createJsonValue(QString const &key, QString const &value = "");
+public:
+    explicit TariffEditor();
+
+    static QByteArray readJson(QString const &filename);
+};
+
+#endif // TARIFF_EDITOR_H_INCLUDED