#include <assert.h>
#include <string.h>
#include <stdlib.h>

#include "qbuf.h"

void qbuf_init(struct qbuf *q, size_t length) {
    assert(q && length);
    memset(q, 0, sizeof(struct qbuf));

    q->data = malloc(q->length = length*2);
    assert(q->data);
}

void qbuf_done(struct qbuf *q) {
    assert(q);
    free(q->data);
}

static void move_to_front(struct qbuf *q) {
    assert(q);

    if (q->index+q->fill <= q->length/2)
        return;

    memmove(q->data, q->data+q->index, q->fill);
    q->index = 0;
}

void* qbuf_push(struct qbuf *q, size_t *l) {
    size_t m;
    assert(q);

    move_to_front(q);
    m = q->length - q->fill - q->index;
    *l = m;
    return q->data + q->index + q->fill;
}

void qbuf_push_validate(struct qbuf *q, size_t l) {
    assert(q);
    q->fill += l;
    assert(q->index+q->fill <= q->length);
}

void* qbuf_pull(struct qbuf *q, size_t *l) {
    assert(q);
    *l = q->fill;
    return q->data + q->index;
}

void qbuf_pull_invalidate(struct qbuf *q, size_t l) {
    assert(q);

    assert(l <= q->fill);
    q->fill -= l;
    q->index += l;

    assert(q->index+q->fill <= q->length);
    if (!q->fill)
        q->index = 0;
}