#include <stdio.h>
#include <stdlib.h>
#include <sys/shm.h>
#include <time.h>
#include <unistd.h>

#define NUM_PROCS 4
#define SHM_SIZE 1024
#define PATHNAME "."
#define PROJ_ID 65

void write_pipes(int pipefds[][2], pid_t pids[]) {
  for (int i = 0; i < NUM_PROCS; i++) {
    // Creation of a pipe (child -> parent)
    if (pipe(pipefds[i]) == -1) {
      perror("[!] Pipe failed");
      exit(EXIT_FAILURE);
    }

    // Creation of a fork
    pids[i] = fork();

    if (pids[i] == -1) {
      perror("[!] Fork failed");
      exit(EXIT_FAILURE);
    }

    // If the fork is successfully created
    if (pids[i] == 0) {
      // Read end of the pipe is closed before writing (sync)
      close(pipefds[i][0]);

      // Random priority in the range 0-19
      srand(time(NULL) ^ getpid());
      int priority = rand() % 20;

      // Writing to the pipe and closing it afterwards (sync)
      write(pipefds[i][1], &priority, sizeof(priority));
      close(pipefds[i][1]);

      printf("[P%d] Wrote %d into pipe\n", i + 1, priority);

      exit(0);
    }
  }
}

void read_pipes(int pipefds[][2], int priorities[]) {
  for (int i = 0; i < NUM_PROCS; i++) {
    // Write end of the pipe is closed before reading (sync)
    close(pipefds[i][1]);

    // Reading from the pipe and closing it afterwards (sync)
    read(pipefds[i][0], &priorities[i], sizeof(priorities[i]));
    close(pipefds[i][0]);

    printf("[INIT] Read %d from P%d\n", priorities[i], i + 1);
  }
}

void write_mem_segment(int priorities[]) {
  int *shm_array;
  int shmid;

  key_t key = ftok(PATHNAME, PROJ_ID);

  // Get the segment identifier
  if ((shmid = shmget(key, SHM_SIZE, 0666)) < 0) {
    perror("[!] Shmget failed");
    exit(EXIT_FAILURE);
  }

  // Attach (system chooses a suitable address)
  if ((shm_array = (int *)shmat(shmid, NULL, 0)) == (int *)-1) {
    perror("[!] Shmat failed");
    exit(EXIT_FAILURE);
  }

  printf("[INIT] Connected to shared segment %d (%p)\n", shmid,
         (void *)&shm_array);

  // Write
  for (int i = 0; i < NUM_PROCS; i++) {
    shm_array[i] = priorities[i];
  }

  // Detach
  shmdt(shm_array);

  printf("[INIT] Wrote priorities to shared memory\n");
}

int main() {
  int pipefds[NUM_PROCS][2];
  pid_t pids[NUM_PROCS];

  // Creation of forks, their respective pipes, and random priorities
  write_pipes(pipefds, pids);

  int priorities[NUM_PROCS];

  // Reading priorities from the pipes
  read_pipes(pipefds, priorities);

  // Attaching and writing priorities to a shared memory segment
  write_mem_segment(priorities);

  return 0;
}