#include <sys/mman.h>
#include <fcntl.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <pthread.h>
#include <stdbool.h>

#define SHM_NAME "/shared_memory"

struct shared_data {
  pthread_mutex_t mutex;
  int counter;
};

struct shm_shared_data {
  int shm_fd;
  struct shared_data *shared_data;
};

void increment_counter(struct shared_data *data) {
  for (int i = 0; i < 100000; i++) {
    if (pthread_mutex_lock(&data->mutex) != 0) {
      perror("pthread_mutex_lock");
    }

    data->counter++;

    if (pthread_mutex_unlock(&data->mutex) != 0) {
      perror("pthread_mutex_unlock");
    }
  }
}

struct shm_shared_data shared_data_open() {
  struct shared_data *shared_data;

  // Create or open a shared memory object
  int shm_fd = shm_open(SHM_NAME, O_CREAT | O_RDWR, S_IRUSR | S_IWUSR);
  if (shm_fd == -1) {
    perror("shm_open");
    exit(EXIT_FAILURE);
  }

  int shm_size = sizeof(struct shared_data);

  if (ftruncate(shm_fd, shm_size) == -1) {
    perror("ftruncate");
    exit(EXIT_FAILURE);
  }

  // Map the shared memory object into the process's address space
  shared_data = mmap(NULL, shm_size, PROT_READ | PROT_WRITE, MAP_SHARED, shm_fd, 0);
  if (shared_data == MAP_FAILED) {
    perror("mmap");
    exit(EXIT_FAILURE);
  }

  struct shm_shared_data shm_shared_data = {
    .shm_fd = shm_fd,
    .shared_data = shared_data
  };

  return shm_shared_data;
}

void shared_data_close(struct shm_shared_data shm_data) {
  // Unmap the shared memory and close the file descriptor
  if (munmap(shm_data.shared_data, sizeof(struct shared_data)) == -1) {
    perror("munmap");
    exit(EXIT_FAILURE);
  }

  if (close(shm_data.shm_fd) == -1) {
    perror("close");
    exit(EXIT_FAILURE);
  }
}

void *thread_callback(void *p) {
  struct shm_shared_data shm_data = shared_data_open();

  increment_counter(shm_data.shared_data);

  shared_data_close(shm_data);

  return NULL;
}

int main() {
  struct shm_shared_data shm_data = shared_data_open();

  pthread_mutexattr_t mutex_attr;
  pthread_mutexattr_init(&mutex_attr);
  pthread_mutexattr_setpshared(&mutex_attr, PTHREAD_PROCESS_SHARED);

  if (pthread_mutex_init(&shm_data.shared_data->mutex, &mutex_attr) < 0) {
    printf("Failed to initialise mutex\n");
    return -1;
  }

  pthread_t thread1;
  pthread_create(&thread1, NULL, thread_callback, NULL);

  pthread_t thread2;
  pthread_create(&thread2, NULL, thread_callback, NULL);

  pthread_join(thread1, NULL);
  pthread_join(thread2, NULL);

  printf("Counter is %d\n", shm_data.shared_data->counter);

  shared_data_close(shm_data);

  // Unlink the shared memory object (aka delete shared memory)
  if (shm_unlink(SHM_NAME) == -1) {
      perror("shm_unlink");
      exit(EXIT_FAILURE);
  }

  return 0;
}