/*
 * Copyright 2007, Hugo Santos. All Rights Reserved.
 * Distributed under the terms of the MIT License.
 */
#ifndef _KERNEL_UTIL_OPEN_HASH_TABLE_H
#define _KERNEL_UTIL_OPEN_HASH_TABLE_H


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

#ifdef _KERNEL_MODE
#	include <KernelExport.h>
#	include <util/kernel_cpp.h>
#	include <util/TypeOperation.h>
#else
#	include <new>
#	include <TypeOperation.h>
#endif


/*!
	The Definition template must have four methods: `HashKey', `Hash',
	`Compare' and `GetLink;. It must also define several types as shown in the
	following example:

	struct Foo {
		int bar;

		Foo* fNext;
	};

	struct HashTableDefinition {
		typedef int		KeyType;
		typedef	Foo		ValueType;

		size_t HashKey(KeyType key) const
		{
			return key >> 1;
		}

		size_t Hash(ValueType* value) const
		{
			return HashKey(value->bar);
		}

		bool Compare(KeyType key, ValueType* value) const
		{
			return value->bar == key;
		}

		ValueType*& GetLink(ValueType* value) const
		{
			return value->fNext;
		}
	};
*/


struct MallocAllocator {
	void* Allocate(size_t size) const
	{
		return malloc(size);
	}

	void Free(void* memory) const
	{
		free(memory);
	}
};


/** Implements an hash table with open hashing, that is, colliding entries are
 * stored in a linked list. The table may be made to adjust its number of slots
 * depending on the load factor (this should be enabled unless the object is to
 * be used at times where memory allocations aren't possible, such as code
 * called by the memory allocator).
 *
 * The link between entries is part of the ValueType stored items, which makes
 * sure the table can always accept new items and will never fail because it is
 * out of memory (except at Init time).
 */
template<typename Definition, bool AutoExpand = true,
	bool CheckDuplicates = false, typename Allocator = MallocAllocator>
class BOpenHashTable {
public:
	typedef BOpenHashTable<Definition, AutoExpand, CheckDuplicates> HashTable;
	typedef typename Definition::KeyType	KeyType;
	typedef typename Definition::ValueType	ValueType;

	static const size_t kMinimumSize = 8;

	// All allocations are of power of 2 lengths.

	// regrowth factor: 200 / 256 = 78.125%
	//                   50 / 256 = 19.53125%

	BOpenHashTable()
		:
		fTableSize(0),
		fItemCount(0),
		fTable(NULL)
	{
	}

	BOpenHashTable(const Definition& definition)
		:
		fDefinition(definition),
		fTableSize(0),
		fItemCount(0),
		fTable(NULL)
	{
	}

	BOpenHashTable(const Definition& definition, const Allocator& allocator)
		:
		fDefinition(definition),
		fAllocator(allocator),
		fTableSize(0),
		fItemCount(0),
		fTable(NULL)
	{
	}

	~BOpenHashTable()
	{
		fAllocator.Free(fTable);
	}

	status_t Init(size_t initialSize = kMinimumSize)
	{
		if (initialSize > 0 && !_Resize(initialSize))
			return B_NO_MEMORY;
		return B_OK;
	}

	size_t TableSize() const
	{
		return fTableSize;
	}

	bool IsEmpty() const
	{
		return fItemCount == 0;
	}

	size_t CountElements() const
	{
		return fItemCount;
	}

	ValueType* Lookup(typename TypeOperation<KeyType>::ConstRefT key) const
	{
		if (fTableSize == 0)
			return NULL;

		size_t index = fDefinition.HashKey(key) & (fTableSize - 1);
		ValueType* slot = fTable[index];

		while (slot) {
			if (fDefinition.Compare(key, slot))
				break;
			slot = _Link(slot);
		}

		return slot;
	}

	status_t Insert(ValueType* value)
	{
		if (fTableSize == 0) {
			if (!_Resize(kMinimumSize))
				return B_NO_MEMORY;
		} else if (AutoExpand && fItemCount >= (fTableSize * 200 / 256))
			_Resize(fTableSize * 2);

		InsertUnchecked(value);
		return B_OK;
	}

	/*! \brief Inserts a value without resizing the table.

		Use this method if you need to insert a value into the table while
		iterating it, as regular insertion can invalidate iterators.
	*/
	void InsertUnchecked(ValueType* value)
	{
		if (CheckDuplicates && _ExhaustiveSearch(value)) {
#ifdef _KERNEL_MODE
			panic("Hash Table: value already in table.");
#else
			debugger("Hash Table: value already in table.");
#endif
		}

		_Insert(fTable, fTableSize, value);
		fItemCount++;
	}

	// TODO: a ValueType* Remove(const KeyType& key) method is missing

	bool Remove(ValueType* value)
	{
		if (!RemoveUnchecked(value))
			return false;

		if (AutoExpand && fTableSize > kMinimumSize
			&& fItemCount < (fTableSize * 50 / 256))
			_Resize(fTableSize / 2);

		return true;
	}

	/*! \brief Removes a value without resizing the table.

		Use this method if you need to remove a value from the table while
		iterating it, as Remove can invalidate iterators.

		Also use this method if you know you are going to reinsert the item soon
		(possibly with a different hash) to avoid shrinking then growing the
		table again.
	*/
	bool RemoveUnchecked(ValueType* value)
	{
		size_t index = fDefinition.Hash(value) & (fTableSize - 1);
		ValueType* previous = NULL;
		ValueType* slot = fTable[index];

		while (slot) {
			ValueType* next = _Link(slot);

			if (value == slot) {
				if (previous)
					_Link(previous) = next;
				else
					fTable[index] = next;
				break;
			}

			previous = slot;
			slot = next;
		}

		if (slot == NULL)
			return false;

		if (CheckDuplicates && _ExhaustiveSearch(value)) {
#ifdef _KERNEL_MODE
			panic("Hash Table: duplicate detected.");
#else
			debugger("Hash Table: duplicate detected.");
#endif
		}

		fItemCount--;
		return true;
	}

	/*!	\brief Removes all elements from the hash table.

		No resizing happens. The elements are not deleted. If \a returnElements
		is \c true, the method returns all elements chained via their hash table
		link.
	*/
	ValueType* Clear(bool returnElements = false)
	{
		if (fItemCount == 0)
			return NULL;

		ValueType* result = NULL;

		if (returnElements) {
			ValueType** nextPointer = &result;

			// iterate through all buckets
			for (size_t i = 0; i < fTableSize; i++) {
				ValueType* element = fTable[i];
				if (element != NULL) {
					// add the bucket to the list
					*nextPointer = element;

					// update nextPointer to point to the fNext of the last
					// element in the bucket
					while (element != NULL) {
						nextPointer = &_Link(element);
						element = *nextPointer;
					}
				}
			}
		}

		memset(this->fTable, 0, sizeof(ValueType*) * this->fTableSize);
		fItemCount = 0;

		return result;
	}

	/*!	If the table needs resizing, the number of bytes for the required
		allocation is returned. If no resizing is needed, 0 is returned.
	*/
	size_t ResizeNeeded() const
	{
		size_t size = fTableSize;
		if (size == 0 || fItemCount >= (size * 200 / 256)) {
			// grow table
			if (size == 0)
				size = kMinimumSize;
			while (fItemCount >= size * 200 / 256)
				size <<= 1;
		} else if (size > kMinimumSize && fItemCount < size * 50 / 256) {
			// shrink table
			while (fItemCount < size * 50 / 256)
				size >>= 1;
			if (size < kMinimumSize)
				size = kMinimumSize;
		}

		if (size == fTableSize)
			return 0;

		return size * sizeof(ValueType*);
	}

	/*!	Resizes the table using the given allocation. The allocation must not
		be \c NULL. It must be of size \a size, which must be a value returned
		earlier by ResizeNeeded(). If the size requirements have changed in the
		meantime, the method free()s the given allocation and returns \c false,
		unless \a force is \c true, in which case the supplied allocation is
		used in any event.
		Otherwise \c true is returned.
		If \a oldTable is non-null and resizing is successful, the old table
		will not be freed, but will be returned via this parameter instead.
	*/
	bool Resize(void* allocation, size_t size, bool force = false,
		void** oldTable = NULL)
	{
		if (!force && size != ResizeNeeded()) {
			fAllocator.Free(allocation);
			return false;
		}

		_Resize((ValueType**)allocation, size / sizeof(ValueType*), oldTable);
		return true;
	}

	/*! \brief Iterator for BOpenHashTable

		The iterator is not invalidated when removing the current element from
		the table, unless the removal triggers a resize.
	*/
	class Iterator {
	public:
		Iterator(const HashTable* table)
			: fTable(table)
		{
			Rewind();
		}

		Iterator(const HashTable* table, size_t index, ValueType* value)
			: fTable(table), fIndex(index), fNext(value) {}

		bool HasNext() const { return fNext != NULL; }

		ValueType* Next()
		{
			ValueType* current = fNext;
			_GetNext();
			return current;
		}

		void Rewind()
		{
			// get the first one
			fIndex = 0;
			fNext = NULL;
			_GetNext();
		}

	protected:
		Iterator() {}

		void _GetNext()
		{
			if (fNext)
				fNext = fTable->_Link(fNext);

			while (fNext == NULL && fIndex < fTable->fTableSize)
				fNext = fTable->fTable[fIndex++];
		}

		const HashTable* fTable;
		size_t fIndex;
		ValueType* fNext;
	};

	Iterator GetIterator() const
	{
		return Iterator(this);
	}

	Iterator GetIterator(typename TypeOperation<KeyType>::ConstRefT key) const
	{
		if (fTableSize == 0)
			return Iterator(this, fTableSize, NULL);

		size_t index = fDefinition.HashKey(key) & (fTableSize - 1);
		ValueType* slot = fTable[index];

		while (slot) {
			if (fDefinition.Compare(key, slot))
				break;
			slot = _Link(slot);
		}

		if (slot == NULL)
			return Iterator(this, fTableSize, NULL);

		return Iterator(this, index + 1, slot);
	}

protected:
	// for g++ 2.95
	friend class Iterator;

	void _Insert(ValueType** table, size_t tableSize, ValueType* value)
	{
		size_t index = fDefinition.Hash(value) & (tableSize - 1);

		_Link(value) = table[index];
		table[index] = value;
	}

	bool _Resize(size_t newSize)
	{
		ValueType** newTable
			= (ValueType**)fAllocator.Allocate(sizeof(ValueType*) * newSize);
		if (newTable == NULL)
			return false;

		_Resize(newTable, newSize);
		return true;
	}

	void _Resize(ValueType** newTable, size_t newSize, void** _oldTable = NULL)
	{
		for (size_t i = 0; i < newSize; i++)
			newTable[i] = NULL;

		if (fTable) {
			for (size_t i = 0; i < fTableSize; i++) {
				ValueType* bucket = fTable[i];
				while (bucket) {
					ValueType* next = _Link(bucket);
					_Insert(newTable, newSize, bucket);
					bucket = next;
				}
			}

			if (_oldTable != NULL)
				*_oldTable = fTable;
			else
				fAllocator.Free(fTable);
		} else if (_oldTable != NULL)
			*_oldTable = NULL;

		fTableSize = newSize;
		fTable = newTable;
	}

	ValueType*& _Link(ValueType* bucket) const
	{
		return fDefinition.GetLink(bucket);
	}

	bool _ExhaustiveSearch(ValueType* value) const
	{
		for (size_t i = 0; i < fTableSize; i++) {
			ValueType* bucket = fTable[i];
			while (bucket) {
				if (bucket == value)
					return true;
				bucket = _Link(bucket);
			}
		}

		return false;
	}

	Definition		fDefinition;
	Allocator		fAllocator;
	size_t			fTableSize;
	size_t			fItemCount;
	ValueType**		fTable;
};

#endif	// _KERNEL_UTIL_OPEN_HASH_TABLE_H