#include <stdlib.h>

#include <time.h>

#include <gtk/gtk.h>

#define ROWS 20

#define COLS 30

const double pi = 3.141592653589793;

const int size = 20;

int field1[COLS][ROWS];

int field2[COLS][ROWS];

GtkWidget *drawing_area;

GtkWidget *toggle_button;

int get_cell(int x, int y) {

  x = (x + COLS)%COLS;

  y = (y + ROWS)%ROWS;

  return field1[x][y];

}

gboolean timeout(gpointer data) {

  if (gtk_toggle_button_get_active(GTK_TOGGLE_BUTTON(toggle_button))) {

    for(int i = 0; i < COLS; ++i) {

      for(int j = 0; j < ROWS; ++j) {

        int count = 0;

        count += get_cell(i-1, j-1);

        count += get_cell(i-1, j);

        count += get_cell(i-1, j+1);

        count += get_cell(i, j-1);

        count += get_cell(i, j+1);

        count += get_cell(i+1, j-1);

        count += get_cell(i+1, j);

        count += get_cell(i+1, j+1);

        if (field1[i][j]) {

          field2[i][j] = (count == 2 || count == 3);

        } else {

          field2[i][j] = (count == 3);

        }

      }

    }

    for(int i = 0; i < COLS; ++i)

      for(int j = 0; j < ROWS; ++j)

        field1[i][j] = field2[i][j];

    gtk_widget_queue_draw(drawing_area);

  }  

  return TRUE;

}

gboolean draw(GtkWidget *widget, cairo_t *cr, gpointer data) {

  cairo_set_source_rgba(cr, 0.9, 0.9, 0.9, 1);

  cairo_paint(cr);

  cairo_set_source_rgba(cr, 0.0, 0.0, 0.0, 1);

  for(int i = 0; i <= COLS; ++i) {

    cairo_move_to(cr, i*size, 0.0);

    cairo_line_to(cr, i*size, ROWS*size);

  }

  for(int j = 0; j < ROWS; ++j) {

    cairo_move_to(cr, 0.0, j*size);

    cairo_line_to(cr, COLS*size, j*size);

  }

  cairo_stroke(cr);

  for(int i = 0; i < COLS; ++i) {

    for(int j = 0; j < ROWS; ++j) {

      if (field1[i][j]) {

        cairo_arc(cr, (i + 0.5)*size, (j + 0.5)*size, 0.5*size, 0.0, 2.0*pi);

        cairo_fill(cr);

      }

    }

  }

  return TRUE;

}

gboolean button_press(GtkWidget *widget, GdkEventButton *event, gpointer data) {

  int x = (int)(event->x)/size;

  int y = (int)(event->y)/size;

  if (x >= 0 && y >= 0 && x < COLS && y < ROWS) {

    field1[x][y] = !field1[x][y];

    gtk_widget_queue_draw(drawing_area);

  }

  return TRUE;

}

void activate(GtkApplication* app, gpointer data) {

  srand(time(NULL));

  GtkWidget *window = gtk_application_window_new (app);

  GtkWidget *hbox = gtk_box_new(GTK_ORIENTATION_HORIZONTAL, 10);

  gtk_container_add(GTK_CONTAINER(window), hbox);

  drawing_area = gtk_drawing_area_new();

  gtk_widget_set_size_request(GTK_WIDGET(drawing_area), COLS*size, ROWS*size);

  gtk_widget_set_hexpand(drawing_area, TRUE);

  gtk_widget_add_events(drawing_area, GDK_BUTTON_PRESS_MASK);

  g_signal_connect(drawing_area, "draw", G_CALLBACK(draw), NULL);

  g_signal_connect(drawing_area, "button-press-event", G_CALLBACK(button_press), NULL);

  gtk_container_add(GTK_CONTAINER(hbox), drawing_area);

  toggle_button = gtk_toggle_button_new_with_label("Start/Stop");

  gtk_widget_set_valign(toggle_button, GTK_ALIGN_START);

  gtk_container_add(GTK_CONTAINER(hbox), toggle_button);

  gtk_widget_show_all(window);

  g_timeout_add(100, timeout, NULL);

}

int main(int argc, char **argv) {

  GtkApplication *application = gtk_application_new(NULL, 0);

  g_signal_connect(application, "activate", G_CALLBACK(activate), NULL);

  int status = g_application_run(G_APPLICATION(application), argc, argv);

  g_object_unref(application);

  return status;

}