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

#define CHILD_NUMBER 1

/* Creates a vector of CHILD_NUMBER pipes. */
void create_pipe(int fd[2]) {
    /* In case of an error exits with code -1 */
    if (pipe(fd) == -1) {
        printf("Error while attempting to create pipe.\n");
        exit(-1);
    }
}

/* Creates CHILD_NUMBER child processes, stores each pid in the pids array and returns each child process id. */
int babymaker() {
    int i;
    pid_t p;

    for (i = 0; i < CHILD_NUMBER; i++) {
        p = fork();
        /* In case of an error exits with code -1 */
        if (p < 0) {
            printf("Error while attempting to create child process nº %d pipe.\n", i + 1);
            exit(-1);
        }
        /* Child process returns it's id */
        if (p == 0) {
            return i + 1;
        }
    }
    /* Parent process returns 0 */
    return 0;
}

void write_value(int fd[2], int value) {
    if (write(fd[1], &value, sizeof(value)) == -1) {
        printf("Error while attempting to write on pipe.\n");
        exit(-1);
    }
}

int read_value(int fd[2], int *value) {
    int status = (int) read(fd[0], value, sizeof(value));
    if (status == -1) {
        printf("Error while attempting to read from pipe.\n");
        exit(-1);
    }
    return status;
}

void close_file_descriptor(int fd[2], int i) {
    if (close(fd[i]) == -1) {
        /* In case of an error exits with value -1 */
        printf("Error while attempting to close file descriptor.\n");
        exit(-1);
    }

}
int main() {
    int id, number, res, parent_to_child[2], child_to_parent[2];

    create_pipe(parent_to_child);
    create_pipe(child_to_parent);

    id = babymaker();

    if (id != 0) {
        close_file_descriptor(parent_to_child,1);
        close_file_descriptor(child_to_parent,0);
        dup2(child_to_parent[1], fileno(stdin));
        execlp("./ex15_simples", "./ex15_simples", (char *) NULL);
        dup2(child_to_parent[0], fileno(stdout));
        close_file_descriptor(parent_to_child,0);
        close_file_descriptor(child_to_parent,1);
    } else {
        close_file_descriptor(parent_to_child,0);
        close_file_descriptor(child_to_parent,1);
        scanf("%d\n", &number);
        write_value(parent_to_child, number);
        close_file_descriptor(parent_to_child,1);
        read_value(child_to_parent,&res);
        close_file_descriptor(child_to_parent,0);
        printf("%d",res);
    }
    return 0;
}