/*
 * File: main.c, author: John Sauter, date: April 7, 2024.
 * Display a digital clock. 
*/

/*
 * Copyright © 2024 by John Sauter <John_Sauter@systemeyescomputerstore.com>

 * This program is free software: you can redistribute it and/or modify
 *  it under the terms of the GNU General Public License as published by
 *  the Free Software Foundation, either version 3 of the License, or
 *  (at your option) any later version.

 *  This program is distributed in the hope that it will be useful,
 *  but WITHOUT ANY WARRANTY; without even the implied warranty of
 *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 *  GNU General Public License for more details.

 *  You should have received a copy of the GNU General Public License
 *  along with this program.  If not, see <https://www.gnu.org/licenses/>.

 *  The author's contact information is as follows:
 *    John Sauter
 *    System Eyes Computer Store
 *    20A Northwest Blvd.  Ste 345
 *    Nashua, NH  03063-4066
 *    telephone: (603) 424-1188
 *    e-mail: John_Sauter@systemeyescomputerstore.com
 */

/*
 * This program is based on the GTK Display Time in Glade Application
 * at https://prognotes.net/2017/05/gtk-display-time-glade-application/.
 */

/* GTK definitions */
#include <gtk/gtk.h>

/* libtime definitions */
#include <time_subroutines.h>

/* Structure passed to the timer handler.  It holds a pointer
 * to the label which is modified to contain the current time,
 * and a flag to tell the timer handler that we are quitting.
 */
typedef struct {
  GtkWidget *w_lbl_time;
  gint quitting;
} app_widgets;

/* Forward reference */
gboolean
timer_handler(app_widgets *widgets);

/* Make sure the operating system isn't concealing leap seconds.  */
static int
test_for_disabled_adjtimex ()
{
  int adjtimex_is_disabled;
  adjtimex_is_disabled = time_test_for_disabled_adjtimex();
  if (adjtimex_is_disabled != 0)
    {
      /* Some high security environments disable the adjtimex function,
       * even when, as here, it is just fetching information.
       * The adjtimex function is the only way to determine that
       * there is a leap second in progress, so complain if it
       * doesn't work. */
      printf ("The current time will not be correct during a leap second\n"
	      "because the Linux adjtimex function is not working.\n");
      exit (EXIT_FAILURE);
    }
  return (0);
}

/* Main program */
int
main(int argc, char *argv[])
{
  GtkBuilder *builder; 
  GtkWidget *window;
  app_widgets *widgets = g_slice_new (app_widgets);
  
  gtk_init (&argc, &argv);
  widgets->quitting = 0;

  test_for_disabled_adjtimex();
  
  /* Load the Glade window description.  */
  builder = gtk_builder_new();
  gtk_builder_add_from_file (builder, "glade/window_main.glade", NULL);

  window = GTK_WIDGET(gtk_builder_get_object(builder, "window_main"));
  widgets->w_lbl_time  = GTK_WIDGET(gtk_builder_get_object(builder,
							     "lbl_time"));
  gtk_builder_connect_signals(builder, widgets);
  g_object_unref(builder);
  
  /* start the 0.1-second timer */
  g_timeout_add (100, (GSourceFunc)timer_handler, widgets);

  /* Show the window.  */
  gtk_widget_show(window);

  /* Run the event loop.  */
  gtk_main();

  /* We have quit.  Free storage and exit.
   * To avoid a race condition with the timer handler, tell it to
   * cancel its timer if it gets called while we are quitting.
   */
  widgets->quitting = 1;
  g_slice_free(app_widgets, widgets);

  return 0;
}

/* handler for the 0.1 second timer tick */
gboolean
timer_handler(app_widgets *widgets)
{
  /* We use libtime instead of GDateTime because GDdateTime is
   * oblivious to leap seconds.  */
  struct tm time1_tm;
  struct tm time2_tm;
  int nanoseconds;
  gchar *fraction_display;
  gchar *final_display;
  gchar buffer1 [128];

  /* If we are quitting, stop the timer.  */
  if (widgets->quitting != 0)
    return FALSE;
  
  /* Get the current time.  */
  time_current_tm_nano (&time1_tm, &nanoseconds);
			  
  /* Convert to local time and use strftime to make a readable display.
   * The Kameron font is a readable font with tabular digits.
   * It can be installed from the Google family of free fonts.
   * Note the '.%.1s' in the output from strftime.  */
  time_UTC_to_local (&time1_tm, &time2_tm, INT_MIN);
  strftime (&buffer1 [0], sizeof (buffer1),
	    "<span font='Kameron' size='36pt'>"
	    "%A, %B %d, %Y, %I:%M:%S.%%.1s %p %Z"
	    "</span>", &time2_tm);
  
  /* Strftime has no provision for outputting fractions of a second,
   * so we put a literal '.%.1s' after the seconds. We will now use
   * the output of strftime as a format string to insert the
   * fraction of a second.  */
  fraction_display = g_strdup_printf ((gchar*) "%09d", nanoseconds);
  final_display = g_strdup_printf ((gchar *) &buffer1 [0],
				   fraction_display);
  
  /* Update the display with the current time.  */
  gtk_label_set_markup (GTK_LABEL(widgets->w_lbl_time), final_display);

  /* Free allocated strings.  */
  g_free (fraction_display);
  fraction_display = NULL;
  g_free (final_display);
  final_display = NULL;
  
  /* Return TRUE so the timer will fire after another tenth of a second.  */
  return TRUE;
}

/* When the window is closed, the application exits.  */
void
on_window_main_destroy()
{
  gtk_main_quit();
}

/* End of file main.c  */