/*
 * Copyright (C) 2010 spy
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are
 * met:
 *
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. The name of the author may not be used to endorse or promote products
 *    derived from this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR "AS IS" AND ANY EXPRESS OR
 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
 * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
 * DISCLAIMED. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT,
 * INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
 * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
 * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
 * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING
 * IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
 * POSSIBILITY OF SUCH DAMAGE.
 */
/*
 * Dynamic hash tables.
 *
 * As usual, nodes with colliding hashes are doubly-linked in a list.
 * However, these hash tables will automatically grow as they become
 * full (they don't shrink back), so to simplify rehashing those lists
 * of nodes are maintained as parts of a super-list containing all
 * nodes in a table. The end of a particular sub-list is not marked in
 * any way, but the very hashes serve to that purpose. Except for the
 * sub-lists, there's no order in the super-list. Refer to the scheme:
 *
 *                 ...+-------+...+-------+...+-------+...+-------+...
 *      .t_table:     |  811  |   | 14023 |   | 19588 |   | 28706 |
 *                 ...+-------+...+-------+...+-------+...+-------+...
 *                        :           :           :           :
 *                        v           v           v           v
 *                      +---+       +---+       +---+       +---+
 *      .t_nodes:  ---->| A |------>| B |     ->| D |     ->| F |....>
 *                      +---+       +---+    /  +---+    /  +---+
 *                                    |     /     |     /
 *                                    v    /      v    /
 *                                  +---+ /     +---+ /
 *                                  | C |-      | E |-
 *                                  +---+       +---+
 */
#include "hash.h"
#include "var.h"
#include <assert.h>
#include <ctype.h>
#include <errno.h>
#include <stdlib.h>
#include <string.h>
#include <strings.h>
#include <sys/types.h>
#include <syslog.h>

/*
 * Internal functions.
 */

/*
 * Bitwise hash function.  Author J. Zobel, April 2001.
 * Permission to use this code is freely granted,
 * provided that this statement is retained.
 */
static int
zobel_hash(hash_table_t *tp, const char *key)
{
    int digest = tp->t_salt;

    while (*key)
        digest ^= (digest << 5) + (digest >> 2) +
            (tp->t_nocase ? tolower(*key++) : *key++);
    return (digest % tp->t_size);
}

static int
realloc_hash_table(hash_table_t *tp, size_t nelem)
{
    hash_node_t *ntp;

    assert(nelem);
    if (!(ntp = calloc(nelem, sizeof (*tp->t_table)))) {
        syslog(LOG_ERR,
    "realloc_hash_table(): calloc() of %i bytes failed (error %i: %s)",
               nelem * sizeof (*tp->t_table), errno, strerror(errno));
        return (-1);
    }
    if (tp->t_table)
        free(tp->t_table);
    tp->t_table = ntp;
    tp->t_size = nelem;
    tp->t_nelem = 0;
    return (0);
}

static void
grow_hash_table(hash_table_t *tp)
{
    size_t oldsize;

    oldsize = tp->t_size;
    /**
     * todo: configurable per-table growth factors
     */
    (void)realloc_hash_table(tp, (size_t)((float)tp->t_size * 1.30f));
    hash_table_rehash(tp, rand());
    syslog(LOG_INFO, "resized hash table %s from %i to %i", tp->t_name,
           oldsize, tp->t_size);
}

static void
insert_node(hash_table_t *tp, hash_node_t *np, hash_node_t **nnpp)
{
    if (*nnpp) {
        np->n_prev = (*nnpp)->n_prev;
        (*nnpp)->n_prev = np;
        if (np->n_prev)
            np->n_prev->n_next = np;
        else {
            assert(tp->t_nodes == *nnpp);
            tp->t_nodes = np;
        }
        np->n_next = *nnpp;
    } else {
        np->n_prev = NULL;
        np->n_next = tp->t_nodes;
        tp->t_nodes = np;
    }
    *nnpp = np;
}

/*
 * Exported functions.
 */

/**
 * todo: salt param
 */
void
hash_init(hash_table_t *tp, const char *name, size_t off, size_t size,
      boolean_t nocase)
{
    assert(name);
    assert(size);
    tp->t_name = name;
    tp->t_off = off;
    tp->t_nocase = nocase;
    tp->t_salt = rand();
    tp->t_nodes = NULL;
    if (realloc_hash_table(tp, size)) {
        syslog(LOG_EMERG,
    "hash_init(): panic: failed to allocate memory for hash table %s",
               name);
        abort();
    }
}

void
hash_fini(hash_table_t *tp)
{
    assert(tp);
    assert(tp->t_table);
    free(tp->t_table);
}

void
hash_node_init(hash_node_t *np, const char *key)
{
    assert(np);
    assert(key);
    np->n_key = key;
    np->n_next = np->n_pprev = NULL;
}

void
hash_table_rehash(hash_table_t *tp, int salt)
{
    hash_node_t *np, *walker;

    assert(tp);
    tp->t_salt = salt;
    walker = tp->t_nodes;
    while (walker) {
        np = walker;
        walker = walker->n_next;
        hash_insert(tp, np);
    }
}

void
hash_insert(hash_table_t *tp, hash_node_t *np)
{
    assert(tp);
    assert(np);
    assert(tp->t_nelem < tp->t_size);
    if (++tp->t_nelem == tp->t_size)
        grow_hash_table(tp);
    insert_node(tp, np, &tp->t_table[zobel_hash(tp, np->n_key)]);
}

void
hash_remove(hash_table_t *tp, hash_node_t *np)
{
    int digest;

    assert(tp);
    assert(np);
    digest = zobel_hash(tp, np->n_key);
    if (tp->t_table[digest] == np)
        tp->t_table[digest] = np->n_next;
    if (np->n_next)
        np->n_next->n_prev = np->n_prev;
    if (tp->t_nodes == np) {
        assert(!np->n_prev);
        tp->t_nodes = np->n_next;
    } else {
        assert(np->n_prev);
        np->n_prev->n_next = np->n_next;
    }
    --tp->t_nelem;
}

void *
hash_find(hash_table_t *tp, const char *key)
{
    hash_node_t *np;
    int digest;

    assert(tp);
    assert(key);
    digest = zobel_hash(tp, key);
    for (np = table->t_table[digest];
         np && zobel_hash(np->n_key, tp->t_size) == digest;
         np = np->n_next)
        if (tp->t_nocase ? !strcasecmp(key, np->n_key) :
            !strcmp(key, np->n_key)) {
            if (*np->n_prev != &tp->t_table[digest]) {
                hash_remove(tp, np);
                insert_node(tp, np, &tp->t_table[digest]);
            }
            return (np - tp->t_off);
        }
    return (NULL);
}