/*
 * CDDL HEADER START
 *
 * This file and its contents are supplied under the terms of the
 * Common Development and Distribution License ("CDDL"), version 1.0.
 * You may only use this file in accordance with the terms of version
 * 1.0 of the CDDL.
 *
 * A full copy of the text of the CDDL should have accompanied this
 * source.  A copy of the CDDL is also available via the Internet at
 * http://www.illumos.org/license/CDDL.
 *
 * CDDL HEADER END
 */

/*
 * Copyright (c) 2012 by Delphix. All rights reserved.
 */

#include <dtrace.h>
#include <dt_impl.h>
#include <dt_pq.h>
#include <assert.h>

/*
 * Create a new priority queue.
 *
 * size is the maximum number of items that will be stored in the priority
 * queue at one time.
 */
dt_pq_t *
dt_pq_init(dtrace_hdl_t *dtp, uint_t size, dt_pq_value_f value_cb, void *cb_arg)
{
        dt_pq_t *p;
        assert(size > 1);

        if ((p = dt_zalloc(dtp, sizeof (dt_pq_t))) == NULL)
                return (NULL);

        p->dtpq_items = dt_zalloc(dtp, size * sizeof (p->dtpq_items[0]));
        if (p->dtpq_items == NULL) {
                dt_free(dtp, p);
                return (NULL);
        }

        p->dtpq_hdl = dtp;
        p->dtpq_size = size;
        p->dtpq_last = 1;
        p->dtpq_value = value_cb;
        p->dtpq_arg = cb_arg;

        return (p);
}

void
dt_pq_fini(dt_pq_t *p)
{
        dtrace_hdl_t *dtp = p->dtpq_hdl;

        dt_free(dtp, p->dtpq_items);
        dt_free(dtp, p);
}

static uint64_t
dt_pq_getvalue(dt_pq_t *p, uint_t index)
{
        void *item = p->dtpq_items[index];
        return (p->dtpq_value(item, p->dtpq_arg));
}

void
dt_pq_insert(dt_pq_t *p, void *item)
{
        uint_t i;

        assert(p->dtpq_last < p->dtpq_size);

        i = p->dtpq_last++;
        p->dtpq_items[i] = item;

        while (i > 1 && dt_pq_getvalue(p, i) < dt_pq_getvalue(p, i / 2)) {
                void *tmp = p->dtpq_items[i];
                p->dtpq_items[i] = p->dtpq_items[i / 2];
                p->dtpq_items[i / 2] = tmp;
                i /= 2;
        }
}

/*
 * Return elements from the priority queue.  *cookie should be zero when first
 * called.  Returns NULL when there are no more elements.
 */
void *
dt_pq_walk(dt_pq_t *p, uint_t *cookie)
{
        (*cookie)++;
        if (*cookie >= p->dtpq_last)
                return (NULL);

        return (p->dtpq_items[*cookie]);
}

void *
dt_pq_pop(dt_pq_t *p)
{
        uint_t i = 1;
        void *ret;

        assert(p->dtpq_last > 0);

        if (p->dtpq_last == 1)
                return (NULL);

        ret = p->dtpq_items[1];

        p->dtpq_last--;
        p->dtpq_items[1] = p->dtpq_items[p->dtpq_last];
        p->dtpq_items[p->dtpq_last] = NULL;

        for (;;) {
                uint_t lc = i * 2;
                uint_t rc = i * 2 + 1;
                uint_t c;
                uint64_t v;
                void *tmp;

                if (lc >= p->dtpq_last)
                        break;

                if (rc >= p->dtpq_last) {
                        c = lc;
                        v = dt_pq_getvalue(p, lc);
                } else {
                        uint64_t lv = dt_pq_getvalue(p, lc);
                        uint64_t rv = dt_pq_getvalue(p, rc);

                        if (lv < rv) {
                                c = lc;
                                v = lv;
                        } else {
                                c = rc;
                                v = rv;
                        }
                }

                if (v >= dt_pq_getvalue(p, i))
                        break;

                tmp = p->dtpq_items[i];
                p->dtpq_items[i] = p->dtpq_items[c];
                p->dtpq_items[c] = tmp;

                i = c;
        }

        return (ret);
}