/*
 * This code is identical to running
 * cat $1 | sort | uniq
 * in bash
 */
#include <stdio.h>
#include <unistd.h>


void run_cat(char* filename, int pfd[2]) {
    dup2(pfd[1], STDOUT_FILENO);
    close(pfd[0]);
    close(pfd[1]);

    char cmd[] = "/usr/bin/cat";
    char *args[] = {"cat", filename, NULL};
    execve(cmd, args, NULL);
}

void run_sort(int pfd1[2], int pfd2[2]) {
    dup2(pfd1[0], STDIN_FILENO);
    dup2(pfd2[1], STDOUT_FILENO);
    close(pfd1[0]);
    close(pfd1[1]);
    close(pfd2[0]);
    close(pfd2[1]);

    char cmd[] = "/usr/bin/sort";
    char *args[] = {"sort", NULL};
    execve(cmd, args, NULL);
}

void run_uniq(int pfd[2]) {
    dup2(pfd[0], STDIN_FILENO);
    close(pfd[0]);
    close(pfd[1]);

    char cmd[] = "/usr/bin/uniq";
    char *args[] = {"uniq", NULL};
    execve(cmd, args, NULL);
}

void check_args(int argc, char** argv) {
    if (argc != 2) {
        printf("Usage: %s <filename>\n", argv[0]);
        _exit(1);
    }
}

int main(int argc, char** argv) {
    int pfd1[2];
    pipe(pfd1);

    int pid = fork();

    if (pid == 0) {
        run_cat(argv[1], pfd1);
    } else {
        close(pfd1[1]);

        int pfd2[2];
        pipe(pfd2);

        int pid2 = fork();

        if (pid2 == 0) {
            run_sort(pfd1, pfd2);
        } else {
            close(pfd1[0]);
            run_uniq(pfd2);
        }
    }
}