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

#define R_FILE "/proc/meminfo"
#define GREP_EXEC "/bin/grep"
#define SORT_EXEC "/bin/sort"
#define HEAD_EXEC "/usr/bin/head"
#define BSIZE 256

int main()
{
    int status;
    pid_t pid_1, pid_2, pid_3;

    int pipe1[2], pipe2[2];

    if (pipe(pipe1) || pipe(pipe2))
    {
       printf("Error with pipes.\n");
       return -1;
    }

    pid_1 = fork();
    if (pid_1 == 0)
    {
      close(pipe1[0]);
      close(pipe2[0]);
      close(pipe2[1]);
      dup2(pipe1[1], STDOUT_FILENO);

        /* grep process */
      execl(GREP_EXEC, "grep", "-cr", "Thread", "nachos/", (char *) 0);

    return 0;
    }

    pid_2 = fork();
    if (pid_2 == 0)
    {
      close(pipe1[1]);
      close(pipe2[0]);
      dup2(pipe1[0], STDIN_FILENO);
      dup2(pipe2[1], STDOUT_FILENO);

        /* sort process */
      execl(SORT_EXEC, "sort", "-t", ":", "+1.0", "-2.0", "--numeric", "--reverse", (char *) 0);
        return 0;
    }

    pid_3 = fork();
    if (pid_3 == 0)
    {
      close(pipe1[0]);
      close(pipe1[1]);
      close(pipe2[1]);
      dup2(pipe2[0], STDIN_FILENO);

        /* head process */
      execl(HEAD_EXEC, "head", "--lines=5", (char *) 0);
        return 0;
    }

    /* shell process */
    /* Remember to close unused pipes! */
    close(pipe1[0]);
    close(pipe1[1]);
    close(pipe2[0]);
    close(pipe2[1]);
    close(STDIN_FILENO);
    close(STDOUT_FILENO);

    if ((waitpid(pid_1, &status, 0)) == -1)
    {
        fprintf(stderr, "Process 1 encountered an error. ERROR%d", errno);
        return EXIT_FAILURE;
    }

    if ((waitpid(pid_2, &status, 0)) == -1)
    {
        fprintf(stderr, "Process 2 encountered an error. ERROR%d", errno);
        return EXIT_FAILURE;
    }

    if ((waitpid(pid_3, &status, 0)) == -1)
    {
        fprintf(stderr, "Process 3 encountered an error. ERROR%d", errno);
        return EXIT_FAILURE;
    }

    return 0;
}