#include <iostream>
#include <cstdlib>

using std::cout;
using std::cerr;
using std::endl;
int MAXLINE = 9000;

//ps -A | grep argv[1] | wc -l
int main(int argc, const char* argv[]) {
  int pid, char_count, ps_pipes[2], wc_pipes[2];
  char line[MAXLINE];

  if (argc != 2) {
    cerr << "Error: invalid number of arguments (" << argc << "). Expecting 2" << endl;
    return 1;
  }

  //The commands are forked in reverse order wc -> grep -> ps

  //create the pipe
  if (pipe(ps_pipes) < 0 && pipe(wc_pipes) < 0) {
    cerr << "Pipe error" << endl;
    return -1;
  }

  pid = fork();//child forked for grep

  if (pid < 0) {
    cerr << "First Fork error" << endl;
    return -1;
  }

  //Parent (wc -l)
  if (pid > 0) {
    wait();//Have to wait for grep to finish

    close(wc_pipes[1]);//close the write pipe, this should write to stdout

    dup2(wc_pipes[0], 0);//set the stdin of the process to the read pipe

    execlp("wc", "wc", "-l", (char*)0);//Replace the process

  } else { //Child (grep argv[1])

    pid = fork();//child forked for ps

    if (pid < 0) {
      cerr << "Second Fork error" << endl;
      return -1;
    }

    //In main child (grep argv[1])
    if (pid > 0) { //in parent (grep argv[1])
      wait();

      close(ps_pipes[1]);//close the write pipe from ps. grep will write to wc_pipes
      close(wc_pipes[0]);

      dup2(ps_pipes[0], 0);//set the stdin of the process to the read pipe
      dup2(wc_pipes[1], 1);//set the stdout of the process to go to wc

      execlp("grep", "grep", argv[1], (char*)0);//Replace the process


    } else {//Grand-Child (ps -A)
      close(ps_pipes[0]);//close the read pipe. ps won't be reading

      dup2(ps_pipes[1], 1);//set the stdout of the process to go to grep

      execlp("ps", "ps", "-A", (char*)0);//Replace the process
    }
  }
  exit(0);
}