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

int main(void) {
    // fork creates 2 identical copies of the program
    // only return value is different
    printf("This is the start of the program.\n");
    int p[2];
    if (pipe(p) == -1) { // reader reads from p[0]
        perror("pipe");  // writer writes to p[1]
        return 1;
    }

    pid_t pid = fork();
    if (pid == -1) {
        perror("fork");  // print why the fork failed
        return 1;
    } else if (pid == 0) {
        close(p[0]); // Close unused read end in child
        FILE *f = fdopen(p[1], "w");
        if (f == NULL) {
            perror("fdopen");
            return 1;
        }
        printf("I am the child because fork() returned %d.\n", pid);
        fprintf(f, "hello parent\n");
        fclose(f);
        close(p[1]); // Close write end after use
    } else {
        close(p[1]); // Close unused write end in parent
        FILE *f = fdopen(p[0], "r");
        if (f == NULL) {
            perror("fdopen");
            return 1;
        }
        printf("I am the parent because fork() returned %d.\n", pid);
        char buf[256];
        if (fgets(buf, sizeof(buf), f) != NULL) {
            printf("I got this message from the child: %s", buf);
        } else {
            perror("fgets");
        }
        fclose(f);
        close(p[0]); // Close read end after use
        wait(NULL); // Wait for child process to terminate
    }

    return 0;
}