#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <fcntl.h>
#include <sys/wait.h>
#include <sys/stat.h>

int main (int argc, char** argv) {
	
	int status, n_read, fd;
	char buf[11];
	pid_t child_pid;
	
	// Open a file
	fd = open ("un.fisier", O_RDONLY);
	if (fd < 0) {
		perror ("open un.fisier");
		exit (EXIT_FAILURE);
	}
	
	// The fork syscall. From here on, two processes will run the code.
	child_pid = fork();
	
	switch (child_pid) {
		
		// fork error
		case -1: 
			perror("fork");
			return EXIT_FAILURE;
		
		// child code
		case 0: {
			printf("Child here. My pid is %d. Parent's pid is %d\n", getpid(), getppid());
			
			sleep(3); // sleep for a while
			
			// read and print some characters from file
			n_read = read(fd, buf, 3);
			if (n_read < 0) {
				perror ("Child:reading file");
				exit (EXIT_FAILURE);
			}
			buf[n_read] = '\0';
			printf("Child here. I've read '%s' from the file. I'm going to finish now\n", buf);
			
			break;
		}
		
		// parent code
		default: {
			
			printf("Parent here. My pid is %d. Child's pid is %d\n", getpid(), child_pid);
			
			// wait for child to end execution
			pid_t waited_pid = waitpid(child_pid, &status, 0);
			if (waited_pid < 0) {
				perror("waitpid");
				return EXIT_FAILURE;
			}
			printf("Parent here. Succesfully waited for child %d\n", waited_pid);
			
			// read and print some characters from file
			n_read = read(fd, buf, 3);
			if (n_read < 0) {
				perror ("Parent:reading file");
				exit (EXIT_FAILURE);
			}
			buf[n_read] = '\0';
			printf("Parent here. I've read '%s' from the file. I'm going to finish now\n", buf);
		}
	}
	
	close(fd);

	return 0;
}