/* ************************************************************************** */
/*                                                                            */
/*                                                        :::      ::::::::   */
/*   limited_resources.c                                :+:      :+:    :+:   */
/*                                                    +:+ +:+         +:+     */
/*   By: ruiferna <ruiferna@student.42porto.com>    +#+  +:+       +#+        */
/*                                                +#+#+#+#+#+   +#+           */
/*   Created: 2025/10/08 19:31:58 by ruiferna          #+#    #+#             */
/*   Updated: 2025/10/09 10:25:31 by ruiferna         ###   ########.fr       */
/*                                                                            */
/* ************************************************************************** */

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

#define STUDENTS 10

/*
- 3 computers (limited access)
- Only 3 students can use the PC at same time
- Implement a "semaphore" (using mutex, counter and condictions)
*/

typedef struct s_shared
{
	int pcs_available;
	int students;
	pthread_mutex_t pcs_available_mutex;
	pthread_mutex_t students_mutex;
}	t_shared;

void *student_routine(void *arg)
{
	/*
	Print when students:
	- Arrive at the library
	- Get a computer  
	- Finish using the computer
	- Leave the library
	*/
	t_shared *shared;
	int student_id;
	 shared = (t_shared *) arg;
	 /* Use a reentrant RNG (rand_r) with a per-thread seed to avoid
		 data races when using rand()/srand() from multiple threads. */
	unsigned int seed = (unsigned int)time(NULL) ^ (unsigned int)(unsigned long)pthread_self();
	 pthread_mutex_lock(&shared->students_mutex);
	shared->students += 1;
	student_id = shared->students;
	printf("[%i] Student %i arrived at the library.\n", student_id, student_id);
	pthread_mutex_unlock(&shared->students_mutex);
	while (1)
	{
		pthread_mutex_lock(&shared->pcs_available_mutex);
		if (shared->pcs_available > 0)
		{
			shared->pcs_available -= 1;
			printf("[%i] Student %i got a computer.\n", student_id, student_id);
			pthread_mutex_unlock(&shared->pcs_available_mutex);
			break;
		}
		else
		{
			pthread_mutex_unlock(&shared->pcs_available_mutex);
			usleep(100);
		}
	}
	int use_time = 2 + (rand_r(&seed) % 4);
	usleep(use_time * 1000000);
	pthread_mutex_lock(&shared->pcs_available_mutex);
	shared->pcs_available += 1;
	printf("[%i] Student %i finished using a computer.\n", student_id, student_id);
	pthread_mutex_unlock(&shared->pcs_available_mutex);
	printf("[%i] Student %i left the library.\n", student_id, student_id);
	return (NULL);
}

int	main()
{
	pthread_t *students;
	t_shared shared;

	shared.pcs_available = 3;
	shared.students = 0;
	pthread_mutex_init(&shared.pcs_available_mutex, NULL);
	pthread_mutex_init(&shared.students_mutex, NULL);
	students = (pthread_t *) malloc (sizeof(pthread_t) * STUDENTS);

	int i = 0;
	while (i < STUDENTS)
	{
		pthread_create(&students[i], NULL, student_routine, &shared);
		i++;
	}
	i = 0;
	while (i < STUDENTS)
	{
		pthread_join(students[i], NULL);
		i++;
	}
	pthread_mutex_destroy(&shared.pcs_available_mutex);
	pthread_mutex_destroy(&shared.students_mutex);
	free(students);
	return (0);
}