//usr/bin/env -S tcc -lm -lX11 -lXxf86vm -run "$0" "$@"; exit $?
/* Not Tetris, but a harmless trap (both for the students and NFS)
 * $Id: ntetris.c,v 1.22 2024/04/04 12:09:01 oj14ozun Exp $
 * https://wwwcip.cs.fau.de/~oj14ozun/src+etc/ntetris.c
 * Distributed under https://creativecommons.org/public-domain/cc0/ */

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <math.h>
#include <signal.h>
#include <sys/wait.h>
#include <stdbool.h>
#include <libgen.h>
#include <sys/prctl.h>

#include <X11/Xlib.h>
#include <X11/extensions/xf86vmode.h>

#define DELTA_T		1e-3
#define SLEEP		10000
#define MIN_CT		0.5
#define P_RE		71
#define P_GR		17
#define P_BL		97
#define SELF_NAME	"tetris"

static Display *dpy;

static void cleanup(int sig)
{
     static volatile bool caught = false;
     if (!caught) {             /* see (libc) Termination in Handler */
          XF86VidModeSetGamma(dpy, DefaultScreen(dpy), &(XF86VidModeGamma){ 1, 1, 1 });
          XCloseDisplay(dpy);
          signal(sig, SIG_DFL);
     }
     raise(sig);
}

int main()
{
     int size;
     char *displayname;
     unsigned short *rr, *gr, *br;
     unsigned short *rr0, *gr0, *br0;
     sigset_t block, prev;

     /* Daemonise into the background */
     switch (fork()) {
     case -1:
          goto fail;
     case 0:		/* child */
          break;
     default:		/* parent */
          return EXIT_SUCCESS;
     }

     /* Initialise X11 connection */
     displayname = getenv("DISPLAY");
     if (!(displayname && displayname[0]))
          goto fail;
     dpy = XOpenDisplay(displayname);
     if (dpy == NULL)
          goto fail;
     XF86VidModeSetGamma(dpy, DefaultScreen(dpy), &(XF86VidModeGamma){ 1, 1, 1 });

     /* Allocate storage for the gamma info */
     XF86VidModeGetGammaRampSize(dpy, DefaultScreen(dpy), &size);
     rr = calloc(sizeof(unsigned short), size);
     if (NULL == rr)
          goto fail;
     gr = calloc(sizeof(unsigned short), size);
     if (NULL == gr)
          goto fail;
     br = calloc(sizeof(unsigned short), size);
     if (NULL == br)
          goto fail;
     XF86VidModeGetGammaRamp(dpy, DefaultScreen(dpy), size, rr, gr, br);
     rr0 = calloc(sizeof(unsigned short), size);
     if (NULL == rr0)
          goto fail;
     gr0 = calloc(sizeof(unsigned short), size);
     if (NULL == gr0)
          goto fail;
     br0 = calloc(sizeof(unsigned short), size);
     if (NULL == br0)
          goto fail;

     /* Μὴ μοῦ τοὺς κύκλους τάραττε. */
     nice(19);
     setsid();
     signal(SIGHUP, SIG_IGN);
     signal(SIGINT, cleanup);
     signal(SIGTERM, cleanup);
     sigemptyset(&block);
     sigaddset(&block, SIGINT);
     sigaddset(&block, SIGTERM);

     /* Rename process to make it easier to find */
     prctl(PR_SET_NAME, (unsigned long)SELF_NAME, 0, 0, 0);

     /* Oh boy fellas, let's rock this joint! */
     for (double t = 0;; t += DELTA_T) {
          double f = 0.5;
          for (int i = 0; i < size; i++) {
               rr0[i] = rr[i] * ((1-f) + f * (1 + cos(t * P_RE)) / 2);
               gr0[i] = gr[i] * ((1-f) + f * (1 + cos(t * P_GR)) / 2);
               br0[i] = br[i] * ((1-f) + f * (1 + cos(t * P_BL)) / 2);
          }

          sigprocmask(SIG_BLOCK, &block, &prev);
          XF86VidModeSetGammaRamp(dpy, DefaultScreen(dpy), size, rr0, gr0, br0);
          usleep(SLEEP);
          sigprocmask(SIG_SETMASK, &prev, NULL);
     }

     abort();
fail:
     /* Intentionally obfuscate the error message */
     fprintf(stderr, "Something went wrong, try again\n");
     return EXIT_FAILURE;
}

/* Local Variables: */
/* compile-command: "cc -o ntetris ntetris.c -lm -lX11 -lXxf86vm" */
/* mode: c */
/* indent-tabs-mode: nil */
/* End: */