#include <stdio.h>
#include <stdlib.h>
#include <signal.h>
#include <unistd.h>
#include <string.h>
#include <siginfo.h>
#include <sys/types.h>

volatile sig_atomic_t current_src;
volatile sig_atomic_t current_sig = -1;
int before = -1;
int after = -1;
int start = 0;

void handler (int sig, siginfo_t * info, void * unused)
{
	if (info && (info->si_code != SI_NOINFO) && (info->si_code <= 0)) {
		current_sig = sig;
		current_src = info->si_pid;
	} else if (start) {
		current_sig = sig;
		current_src = -1;
	}
}

int main (int argc, char ** argv)
{
	struct sigaction act;
	char c;

	act.sa_sigaction = handler;
	act.sa_flags = SA_SIGINFO;
	sigemptyset (&act.sa_mask);
	sigaddset (&act.sa_mask, SIGUSR1);
	sigaddset (&act.sa_mask, SIGTERM);
	sigaddset (&act.sa_mask, SIGINT);
	if (sigaction (SIGUSR1, &act, NULL)) {
		perror ("sigaction");
		return 1;
	}
	if (sigaction (SIGUSR2, &act, NULL)) {
		perror ("sigaction");
		return 1;
	}
	if (sigaction (SIGINT, &act, NULL)) {
		perror ("sigaction");
		return 1;
	}
	if (sigaction (SIGTERM, &act, NULL)) {
		perror ("sigaction");
		return 1;
	}
	switch (argc) {
	case 1:
		break;
	case 3:
		if (strcmp (argv[2], "start") != 0) {
			fprintf (stderr, "usage: %s [ pid [start] ]\n", argv[0]);
			return 1;
		}
		start = 1;
		/* Fall though */
	case 2:
		if (sscanf (argv[1], "%d%c", &after, &c) == 1)
			break;
		/* Fall through */
	default:
		fprintf (stderr, "usage: %s [ pid [start] ]\n", argv[0]);
		/* Fall through */
	case 0:
		/* Can't output a usage message without argv[0]! */
		return 1;
	}
	while (1) {
		int this_sig, this_src;
		while (current_sig < 0)
			pause ();
		sighold (SIGUSR1);
		sighold (SIGUSR2);
		sighold (SIGTERM);
		sighold (SIGINT);
		this_sig = current_sig;
		this_src = current_src;
		current_sig = -1;
		sigrelse (SIGUSR1);
		sigrelse (SIGUSR2);
		sigrelse (SIGTERM);
		sigrelse (SIGINT);
		if (this_sig < 0)
			continue;
		printf ("Jupp (sig = %d, me = %d)\n", this_sig, (int)getpid ());
		if ((start && (this_src < 0)) || (this_src != after)) {
			if (!start)
				before = this_src;
			if (after < 0) {
				printf ("Bounce (sig = %d, me = %d)\n", this_sig, (int)getpid ());
				this_src = after;
			} else 
				kill (after, this_sig);
		}
		if (this_src == after) {
			if (before >= 0)
				kill (before, this_sig);
			else
				printf ("Drop (sig = %d, me = %d)\n", this_sig, (int)getpid ());
			if ((this_sig == SIGTERM) || (this_sig == SIGINT))
				break;
		}
	}
	return 0;
}