#include <stdlib.h>
#include "queue.h"
#include <pthread.h>

/* Remember to initilize the queue before using it */
void initialize_queue(struct pqueue_t *q)
{
	q->head = q->tail = NULL;
	pthread_mutex_init(&q->lock, NULL);
}

/* Return non-zero if the queue is empty */
int empty(struct pqueue_t *q)
{
	return (q->head == NULL);
}

/* Get PCB of a process from the queue (q).
 * Return NULL if the queue is empty */
struct pcb_t *de_queue(struct pqueue_t *q)
{
	struct pcb_t *proc = NULL;
	// TODO: return q->head->data and remember to update the queue's head
	// and tail if necessary. Remember to use 'lock' to avoid race
	// condition

	// YOUR CODE HERE
	if (empty(q))
		return NULL;
	pthread_mutex_lock(&q->lock);
	proc = q->head->data;
	struct qitem_t *pdel = q->head;
	if (q->head == q->tail)
		q->head = q->tail = NULL;
	else
		q->head = q->head->next;
	free(pdel);
	pthread_mutex_unlock(&q->lock);

	return proc;
}

/* Put PCB of a process to the queue. */
void en_queue(struct pqueue_t *q, struct pcb_t *proc)
{
	// TODO: Update q->tail.
	// Remember to use 'lock' to avoid race condition

	// YOUR CODE HERE
	pthread_mutex_lock(&q->lock);
	struct qitem_t *new_data = malloc(sizeof(struct qitem_t));
	if (new_data == NULL)
		return;
	new_data->data = proc;
	new_data->next = NULL;
	if (empty(q))
	{
		q->head = q->tail = new_data;
	}
	else
	{
		q->tail->next = new_data;
		q->tail = q->tail->next;
	}
	pthread_mutex_unlock(&q->lock);
}