/* Copyright (c) 2000, 2021, Oracle and/or its affiliates.

   This program is free software; you can redistribute it and/or modify
   it under the terms of the GNU General Public License, version 2.0,
   as published by the Free Software Foundation.

   This program is also distributed with certain software (including
   but not limited to OpenSSL) that is licensed under separate terms,
   as designated in a particular file or component or in included license
   documentation.  The authors of MySQL hereby grant you an additional
   permission to link the program and your derivative works with the
   separately licensed software that they have included with MySQL.

   This program is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   GNU General Public License, version 2.0, for more details.

   You should have received a copy of the GNU General Public License
   along with this program; if not, write to the Free Software Foundation,
   51 Franklin Street, Suite 500, Boston, MA 02110-1335 USA */


/*
** A class for static sized hash tables where old entries are deleted in
** first-in-last-out to usage.
*/

#ifndef  HASH_FILO_H
#define  HASH_FILO_H

#include "hash.h"        /* my_hash_get_key, my_hash_free_key, HASH */
#include "mysqld.h"      /* key_hash_filo_lock */

struct hash_filo_element
{
private:
  hash_filo_element *next_used,*prev_used;
public:
  hash_filo_element() {}
  hash_filo_element *next()
  { return next_used; }
  hash_filo_element *prev()
  { return prev_used; }
  
  friend class hash_filo;
};


class hash_filo
{
private:
  PSI_memory_key m_psi_key;
  const uint key_offset, key_length;
  const my_hash_get_key get_key;
  /** Size of this hash table. */
  uint m_size;
  my_hash_free_key free_element;
  CHARSET_INFO *hash_charset;

  hash_filo_element *first_link,*last_link;
public:
  mysql_mutex_t lock;
  HASH cache;

  hash_filo(PSI_memory_key psi_key,
            uint size, uint key_offset_arg , uint key_length_arg,
	    my_hash_get_key get_key_arg, my_hash_free_key free_element_arg,
	    CHARSET_INFO *hash_charset_arg)
    : m_psi_key(psi_key),
    key_offset(key_offset_arg), key_length(key_length_arg),
    get_key(get_key_arg), m_size(size),
    free_element(free_element_arg),
    hash_charset(hash_charset_arg),
    first_link(NULL),
    last_link(NULL)
  {
    memset(&cache, 0, sizeof(cache));
    mysql_mutex_init(key_hash_filo_lock, &lock, MY_MUTEX_INIT_FAST);
  }

  ~hash_filo()
  {
    if (cache.array.buffer)	/* Avoid problems with thread library */
      my_hash_free(&cache);
    mysql_mutex_destroy(&lock);
  }
  void clear(bool locked=0)
  {
    if (!locked)
      mysql_mutex_lock(&lock);
    first_link= NULL;
    last_link= NULL;
    my_hash_free(&cache);
    (void) my_hash_init(&cache, hash_charset, m_size, key_offset,
                        key_length, get_key, free_element, 0, m_psi_key);
    if (!locked)
      mysql_mutex_unlock(&lock);
  }

  hash_filo_element *first()
  {
    mysql_mutex_assert_owner(&lock);
    return first_link;
  }

  hash_filo_element *last()
  {
    mysql_mutex_assert_owner(&lock);
    return last_link;
  }

  hash_filo_element *search(uchar* key, size_t length)
  {
    mysql_mutex_assert_owner(&lock);

    hash_filo_element *entry=(hash_filo_element*)
      my_hash_search(&cache, key, length);
    if (entry)
    {						// Found; link it first
      assert(first_link != NULL);
      assert(last_link != NULL);
      if (entry != first_link)
      {						// Relink used-chain
	if (entry == last_link)
        {
	  last_link= last_link->prev_used;
          /*
            The list must have at least 2 elements,
            otherwise entry would be equal to first_link.
          */
          assert(last_link != NULL);
          last_link->next_used= NULL;
        }
	else
	{
          assert(entry->next_used != NULL);
          assert(entry->prev_used != NULL);
	  entry->next_used->prev_used = entry->prev_used;
	  entry->prev_used->next_used = entry->next_used;
	}
        entry->prev_used= NULL;
        entry->next_used= first_link;

        first_link->prev_used= entry;
        first_link=entry;
      }
    }
    return entry;
  }

  my_bool add(hash_filo_element *entry)
  {
    if (!m_size) return 1;
    if (cache.records == m_size)
    {
      hash_filo_element *tmp=last_link;
      last_link= last_link->prev_used;
      if (last_link != NULL)
      {
        last_link->next_used= NULL;
      }
      else
      {
        /* Pathological case, m_size == 1 */
        first_link= NULL;
      }
      my_hash_delete(&cache,(uchar*) tmp);
    }
    if (my_hash_insert(&cache,(uchar*) entry))
    {
      if (free_element)
	(*free_element)(entry);		// This should never happen
      return 1;
    }
    entry->prev_used= NULL;
    entry->next_used= first_link;
    if (first_link != NULL)
      first_link->prev_used= entry;
    else
      last_link= entry;
    first_link= entry;

    return 0;
  }

  uint size()
  { return m_size; }

  void resize(uint new_size)
  {
    mysql_mutex_lock(&lock);
    m_size= new_size;
    clear(true);
    mysql_mutex_unlock(&lock);
  }
};

#endif
