#include <stdlib.h>

#include <skipstone/queue.h>

struct entry {
    void *value;
    struct entry *next, *prev;
};

struct _skipstone_queue {
    size_t count;
    struct entry *last;
};

skipstone_queue *skipstone_queue_new() {
    skipstone_queue *queue;

    if ((queue = malloc(sizeof(*queue))) == NULL) {
        goto error_malloc_queue;
    }

    queue->count = 0;
    queue->last  = NULL;

    return queue;

error_malloc_queue:
    return NULL;
}

size_t skipstone_queue_count(skipstone_queue *queue) {
    return queue->count;
}

int skipstone_queue_push(skipstone_queue *queue, void *value) {
    struct entry *next;

    if ((next = malloc(sizeof(*entry))) == NULL) {
        goto error_malloc_next;
    }

    next->value = value;
    next->next  = NULL;
    next->prev  = NULL;

    queue->last->next = next;
    queue->last       = next;

    return 0;

error_malloc_next:
    return -1;
}

int skipstone_queue_pop(skipstone_queue *queue, void **value) {
    struct entry *last = queue->last;

    if (last == NULL) {
        return 0;
    }

    queue->last = last->prev;

    free(last);

    return 0;
}