#include <gtk/gtk.h>

GtkWidget *txtResult = 0;

void button_clicked(GtkWidget *widget, gpointer data) {

  gchar *result;
  result = "Ergebnis";
  gtk_entry_set_text (txtResult,result);
}

static void activate (GtkApplication* app, gpointer user_data)
{
    // Mainwindow
    GtkWidget *window;
    window = gtk_application_window_new(app);

    // Top level container
    GtkWidget *vbox;
    vbox = gtk_box_new(GTK_ORIENTATION_VERTICAL, 10);
    gtk_container_add(GTK_CONTAINER(window), vbox);

    // Add a caption (first "row")
    GtkWidget *lblCaption;
    lblCaption = gtk_label_new("Berechnung des Kraftstoffverbrauchs");
    gtk_box_pack_start(GTK_BOX(vbox), lblCaption, FALSE, FALSE, 5);


    // Distance entry
    // ----------------------------------------------------
    // Container for the distance
    GtkWidget *hboxDistance;

    // Label distance
    GtkWidget *lblDistance;

    // Textfield distance
    GtkWidget *txtDistance;

    // Create a vertical container box
    hboxDistance = gtk_box_new(GTK_ORIENTATION_HORIZONTAL, 10);
    gtk_container_add(GTK_CONTAINER(window), hboxDistance);

    // Add first the label and then the textfield to the horizontal box
    lblDistance = gtk_label_new("Gefahrene Gesamtstrecke:");
    gtk_box_set_spacing(hboxDistance,16); // Adjust label width
    gtk_box_pack_start(GTK_BOX(hboxDistance), lblDistance, FALSE, FALSE, 5);

    txtDistance = gtk_entry_new(); // Empty textfield
    gtk_box_pack_start(GTK_BOX(hboxDistance), txtDistance, TRUE, TRUE, 5);
    // ----------------------------------------------------

    //Now add this hboxDistance Container as an entry (second row)
    gtk_box_pack_start(GTK_BOX(vbox), hboxDistance, FALSE, FALSE, 5);


    // ----------------------------------------------------
    // Fuel entry -----------------------------------------
    // ----------------------------------------------------
    // Container for the distance
    GtkWidget *hboxFuel;

    // Label distance
    GtkWidget *lblFuel;

    // Textfield distance
    GtkWidget *txtFuel;

    // Create a vertical container box
    hboxFuel = gtk_box_new(GTK_ORIENTATION_HORIZONTAL, 10);
    gtk_container_add(GTK_CONTAINER(window), hboxFuel);

    // Add first the label and then the textfield to the horizontal box
    lblFuel = gtk_label_new("Gesamtverbrauch in Litern:");
    gtk_box_pack_start(GTK_BOX(hboxFuel), lblFuel, FALSE, FALSE, 5);

    txtFuel = gtk_entry_new(); // Empty textfield
    gtk_box_pack_start(GTK_BOX(hboxFuel), txtFuel, TRUE, TRUE, 5);
    // ----------------------------------------------------

    //Now add this hboxFuel Container as an entry (third row)
    gtk_box_pack_start(GTK_BOX(vbox), hboxFuel, FALSE, FALSE, 5);

    // Create and add button to the container(fourth row)
    GtkWidget *btnCalc = gtk_button_new_with_label("Berechnen");
    gtk_box_pack_start(GTK_BOX(vbox), btnCalc, FALSE, FALSE, 5);

    txtResult = gtk_entry_new();
    gtk_box_pack_start(GTK_BOX(vbox), txtResult, TRUE, TRUE, 5);

    // Create signal on button click event
    g_signal_connect(G_OBJECT(btnCalc), "clicked", G_CALLBACK(button_clicked), NULL);

    g_signal_connect(G_OBJECT(window), "destroy",
    G_CALLBACK(gtk_main_quit), NULL);

    gtk_widget_show_all(window);
}

int main (int argc, char *argv[])
{
    GtkApplication *app;
    int status;

    app     = gtk_application_new("", G_APPLICATION_FLAGS_NONE);
    g_signal_connect(app, "activate", G_CALLBACK (activate), NULL);
    status  = g_application_run(G_APPLICATION (app), argc, argv);
    g_object_unref(app);

    return status;
}