/*
 * Copyright (C) 2008-2010 Tobias Brunner
 * Hochschule fuer Technik Rapperswil
 *
 * This program is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License as published by the
 * Free Software Foundation; either version 2 of the License, or (at your
 * option) any later version.  See <http://www.fsf.org/copyleft/gpl.txt>.
 *
 * 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
 * for more details.
 */

#include <utils/linked_list.h>

#include "hashtable.h"

/** The maximum capacity of the hash table (MUST be a power of 2) */
#define MAX_CAPACITY (1 << 30)

typedef struct pair_t pair_t;

/**
 * This pair holds a pointer to the key and value it represents.
 */
struct pair_t {
	/**
	 * Key of a hash table item.
	 */
	void *key;

	/**
	 * Value of a hash table item.
	 */
	void *value;

	/**
	 * Cached hash (used in case of a resize).
	 */
	u_int hash;
};

/**
 * Creates an empty pair object.
 */
pair_t *pair_create(void *key, void *value, u_int hash)
{
	pair_t *this;

	INIT(this,
		.key = key,
		.value = value,
		.hash = hash,
	);

	return this;
}

typedef struct private_hashtable_t private_hashtable_t;

/**
 * Private data of a hashtable_t object.
 *
 */
struct private_hashtable_t {
	/**
	 * Public part of hash table.
	 */
	hashtable_t public;

	/**
	 * The number of items in the hash table.
	 */
	u_int count;

	/**
	 * The current capacity of the hash table (always a power of 2).
	 */
	u_int capacity;

	/**
	 * The current mask to calculate the row index (capacity - 1).
	 */
	u_int mask;

	/**
	 * The load factor.
	 */
	float load_factor;

	/**
	 * The actual table.
	 */
	linked_list_t **table;

	/**
	 * The hashing function.
	 */
	hashtable_hash_t hash;

	/**
	 * The equality function.
	 */
	hashtable_equals_t equals;
};

typedef struct private_enumerator_t private_enumerator_t;

/**
 * hash table enumerator implementation
 */
struct private_enumerator_t {

	/**
	 * implements enumerator interface
	 */
	enumerator_t enumerator;

	/**
	 * associated hash table
	 */
	private_hashtable_t *table;

	/**
	 * current row index
	 */
	u_int row;

	/**
	 * enumerator for the current row
	 */
	enumerator_t *current;
};

/**
 * Compare a pair in a list with the given key.
 */
static inline bool pair_equals(pair_t *pair, private_hashtable_t *this, void *key)
{
	return this->equals(key, pair->key);
}

/**
 * This function returns the next-highest power of two for the given number.
 * The algorithm works by setting all bits on the right-hand side of the most
 * significant 1 to 1 and then increments the whole number so it rolls over
 * to the nearest power of two. Note: returns 0 for n == 0
 */
static u_int get_nearest_powerof2(u_int n)
{
	u_int i;

	--n;
	for (i = 1; i < sizeof(u_int) * 8; i <<= 1)
	{
		n |= n >> i;
	}
	return ++n;
}

/**
 * Init hash table parameters
 */
static void init_hashtable(private_hashtable_t *this, u_int capacity)
{
	capacity = max(1, min(capacity, MAX_CAPACITY));
	this->capacity = get_nearest_powerof2(capacity);
	this->mask = this->capacity - 1;
	this->load_factor = 0.75;

	this->table = calloc(this->capacity, sizeof(linked_list_t*));
}

/**
 * Double the size of the hash table and rehash all the elements.
 */
static void rehash(private_hashtable_t *this)
{
	linked_list_t **old_table;
	u_int row, old_capacity;

	if (this->capacity < MAX_CAPACITY)
	{
		return;
	}

	old_capacity = this->capacity;
	old_table = this->table;

	init_hashtable(this, old_capacity << 1);

	for (row = 0; row < old_capacity; row++)
	{
		enumerator_t *enumerator;
		linked_list_t *list, *new_list;
		pair_t *pair;
		u_int new_row;

		list = old_table[row];
		if (list)
		{
			enumerator = list->create_enumerator(list);
			while (enumerator->enumerate(enumerator, &pair))
			{
				new_row = pair->hash & this->mask;

				list->remove_at(list, enumerator);
				new_list = this->table[new_row];
				if (!new_list)
				{
					new_list = this->table[new_row] = linked_list_create();
				}
				new_list->insert_last(new_list, pair);
			}
			enumerator->destroy(enumerator);
			list->destroy(list);
		}
	}
	free(old_table);
}

METHOD(hashtable_t, put, void*,
	   private_hashtable_t *this, void *key, void *value)
{
	void *old_value = NULL;
	linked_list_t *list;
	u_int hash;
	u_int row;

	hash = this->hash(key);
	row = hash & this->mask;
	list = this->table[row];
	if (list)
	{
		enumerator_t *enumerator;
		pair_t *pair;

		enumerator = list->create_enumerator(list);
		while (enumerator->enumerate(enumerator, &pair))
		{
			if (pair_equals(pair, this, key))
			{
				old_value = pair->value;
				pair->value = value;
				break;
			}
		}
		enumerator->destroy(enumerator);
	}
	else
	{
		list = this->table[row] = linked_list_create();
	}
	if (!old_value)
	{
		list->insert_last(list, pair_create(key, value, hash));
		this->count++;
	}
	if (this->count >= this->capacity * this->load_factor)
	{
		rehash(this);
	}
	return old_value;
}

METHOD(hashtable_t, get, void*,
	   private_hashtable_t *this, void *key)
{
	void *value = NULL;
	linked_list_t *list;
	pair_t *pair;

	list = this->table[this->hash(key) & this->mask];
	if (list)
	{
		if (list->find_first(list, (linked_list_match_t)pair_equals,
							 (void**)&pair, this, key) == SUCCESS)
		{
			value = pair->value;
		}
	}
	return value;
}

METHOD(hashtable_t, remove_, void*,
	   private_hashtable_t *this, void *key)
{
	void *value = NULL;
	linked_list_t *list;

	list = this->table[this->hash(key) & this->mask];
	if (list)
	{
		enumerator_t *enumerator;
		pair_t *pair;

		enumerator = list->create_enumerator(list);
		while (enumerator->enumerate(enumerator, &pair))
		{
			if (pair_equals(pair, this, key))
			{
				list->remove_at(list, enumerator);
				value = pair->value;
				this->count--;
				free(pair);
				break;
			}
		}
		enumerator->destroy(enumerator);
	}
	return value;
}

METHOD(hashtable_t, get_count, u_int,
	   private_hashtable_t *this)
{
	return this->count;
}

METHOD(enumerator_t, enumerate, bool,
	   private_enumerator_t *this, void **key, void **value)
{
	while (this->row < this->table->capacity)
	{
		if (this->current)
		{
			pair_t *pair;

			if (this->current->enumerate(this->current, &pair))
			{
				if (key)
				{
					*key = pair->key;
				}
				if (value)
				{
					*value = pair->value;
				}
				return TRUE;
			}
			this->current->destroy(this->current);
			this->current = NULL;
		}
		else
		{
			linked_list_t *list;

			list = this->table->table[this->row];
			if (list)
			{
				this->current = list->create_enumerator(list);
				continue;
			}
		}
		this->row++;
	}
	return FALSE;
}

METHOD(enumerator_t, enumerator_destroy, void,
	   private_enumerator_t *this)
{
	if (this->current)
	{
		this->current->destroy(this->current);
	}
	free(this);
}

METHOD(hashtable_t, create_enumerator, enumerator_t*,
	   private_hashtable_t *this)
{
	private_enumerator_t *enumerator;

	INIT(enumerator,
		.enumerator = {
			.enumerate = (void*)_enumerate,
			.destroy = (void*)_enumerator_destroy,
		},
		.table = this,
	);

	return &enumerator->enumerator;
}

METHOD(hashtable_t, destroy, void,
	   private_hashtable_t *this)
{
	linked_list_t *list;
	u_int row;

	for (row = 0; row < this->capacity; row++)
	{
		list = this->table[row];
		if (list)
		{
			list->destroy_function(list, free);
		}
	}
	free(this->table);
	free(this);
}

/*
 * Described in header.
 */
hashtable_t *hashtable_create(hashtable_hash_t hash, hashtable_equals_t equals,
							  u_int capacity)
{
	private_hashtable_t *this;

	INIT(this,
		.public = {
			.put = _put,
			.get = _get,
			.remove = _remove_,
			.get_count = _get_count,
			.create_enumerator = _create_enumerator,
			.destroy = _destroy,
		},
		.hash = hash,
		.equals = equals,
	);

	init_hashtable(this, capacity);

	return &this->public;
}