#include <iostream>
#include <fcntl.h>
#include <sys/stat.h>
#include <unistd.h>
#include <sys/wait.h>

using namespace std;

void Parent(int file);
void Child(int file);

int main() {
    int file;
    //int flags{O_CREAT | O_RDWR | O_DIRECT | O_TRUNC};
    int flags{O_CREAT | O_RDWR | O_TRUNC};
    char c;

    srand(time(nullptr));

    mode_t perms{S_IRUSR | S_IWUSR | S_IRGRP | S_IROTH }; 
  
    // open a file and write the alphabet.
    file = open("alphabet", flags, perms);
    for( int i =0; i < 26; ++i) {
        c = static_cast<char>('A' + i);
        write(file, &c, sizeof(char));
        cout << "Writign a " << c << endl;
    }

    // now fork
    pid_t pid {fork()};
    if (pid == -1) {
       perror("Fork Faild");
       exit(0);
    }

    if (pid == 0) {
       Child(file);
    } else {
       int status;
       Parent(file);
       wait(&status);
    }

    return 0; 
}

void Parent(int file){
   // open the pipe for reading.
   // when we successfully read anything from the pipe
   //     seek to 0
   //     print the position.
   int pipeFD = open("mypipe", O_RDONLY);

   char c;
   int numread;
   ssize_t pos;

   while ((numread = read(pipeFD, &c, sizeof(char))) > 0) {
       cout << "Parent: I am checking the file" << endl;
       pos = lseek(file, 0, SEEK_CUR);
       read(file, &c, sizeof(char));
       cout << "Parent: The offset is currently at " << pos << endl;
       cout << "Parent: Just got a " << c << " from the file" << endl;
       cout << endl;
   }

   return;
}

void Child(int file){
   int pipeFD = open("mypipe", O_WRONLY);
   int len;
   char x{'a'};

   len = lseek(file,0, SEEK_END);
   cout << "Child: The file length is " << len << endl;

   for(int i = 0; i < 3; ++i) {
      size_t offset = rand() % len;

      // tell the user what is up.
      cout << "Child: Iteration " << i << endl;
      cout << "Child: seeking to  " << offset << endl;
      cout << "Child: writing a " << x << endl;

      // do the action
      lseek(file, offset,  SEEK_SET); 
      write(file, &x, sizeof(char));
      // back up one so the other proc reads the x
      lseek(file, -1, SEEK_CUR);  
      x = static_cast<char>(x + 1);

      cout << endl;
 
      // tell the  other proc to move on.
      write(pipeFD, &x, sizeof(char));
      sleep(1);
    }
}