/*
 * 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 3 of the License, or (at your option) any later
 * version.
 * 
 * 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.
 * 
 * You should have received a copy of the GNU General Public License along with
 * this program. If not, see <http://www.gnu.org/licenses/>.
 */
package com.l2jserver.gameserver.util;

import java.util.Iterator;
import java.util.NoSuchElementException;

import com.l2jserver.gameserver.model.L2Object;

/**
 * This class is a highly optimized hash table, where keys are integers.<br>
 * The main goal of this class is to allow concurrent read/iterate and write access to this table, plus minimal used memory.<br>
 * This class uses plain array as the table of values, and keys are used to get position in the table.<br>
 * If the position is already busy, we iterate to the next position, until we find the needed element or null.<br>
 * To iterate over the table (read access) we may simply iterate through table array.<br>
 * In case we remove an element from the table, we check - if the next position is null, we reset table's slot to null, otherwise we assign it to a dummy value.
 * @param <T> type of values stored in this hash table.
 * @author mkizub
 */
public final class L2ObjectHashMap<T extends L2Object> extends L2ObjectMap<T>
{
	private static final boolean TRACE = false;
	private static final boolean DEBUG = false;
	
	private static final int[] PRIMES = {
		5, 7, 11, 17, 23, 29, 37, 47, 59, 71, 89, 107, 131, 163, 197, 239, 293,
		353, 431, 521, 631, 761, 919, 1103, 1327, 1597, 1931, 2333, 2801,
		3371, 4049, 4861, 5839, 7013, 8419, 10103, 12143, 14591, 17519,
		21023, 25229, 30293, 36353, 43627, 52361, 62851, 75431, 90523,
		108631, 130363, 156437, 187751, 225307, 270371, 324449, 389357,
		467237, 560689, 672827, 807403, 968897, 1162687, 1395263, 1674319,
		2009191, 2411033, 2893249, 3471899, 4166287, 4999559, 5999471, 7199369
	};
	
	private T[] _table;
	private int[] _keys;
	private int _count;
	
	private static int getPrime(int min)
	{
		for (int element : PRIMES)
		{
			if (element >= min)
			{
				return element;
			}
		}
		throw new OutOfMemoryError();
	}
	
	@SuppressWarnings("unchecked")
	public L2ObjectHashMap()
	{
		int size = PRIMES[0];
		_table = (T[])new L2Object[size];
		_keys = new int[size];
		if (DEBUG)
		{
			check();
		}
	}
	
	@Override
	public int size()
	{
		return _count;
	}
	
	@Override
	public boolean isEmpty()
	{
		return _count == 0;
	}
	
	@Override
	@SuppressWarnings("unchecked")
	public synchronized void clear()
	{
		int size = PRIMES[0];
		_table = (T[])new L2Object[size];
		_keys = new int[size];
		_count = 0;
		if (DEBUG)
		{
			check();
		}
	}
	
	private void check()
	{
		if (DEBUG)
		{
			int cnt = 0;
			for (int i=0; i < _table.length; i++)
			{
				L2Object obj = _table[i];
				if (obj == null) {
					assert (_keys[i] == 0) || (_keys[i] == 0x80000000);
				} else {
					cnt++;
					assert obj.getObjectId() == (_keys[i] & 0x7FFFFFFF);
				}
			}
			assert cnt == _count;
		}
	}
	
	@Override
	public synchronized void put(T obj)
	{
		if (_count >= (_table.length/2))
		{
			expand();
		}
		final int hashcode = obj.getObjectId();
		assert hashcode > 0;
		int seed = hashcode;
		int incr = 1 + (((seed >> 5) + 1) % (_table.length - 1));
		int ntry = 0;
		int slot = -1; // keep last found slot
		do
		{
			int pos = (seed % _table.length) & 0x7FFFFFFF;
			if (_table[pos] == null)
			{
				if (slot < 0)
				{
					slot = pos;
				}
				if (_keys[pos] >= 0) {
					// found an empty slot without previous collisions,
					// but use previously found slot
					_keys[slot] = hashcode;
					_table[slot] = obj;
					_count++;
					if (TRACE)
					{
						System.err.println("ht: put obj id="+hashcode+" at slot="+slot);
					}
					if (DEBUG)
					{
						check();
					}
					return;
				}
			}
			else
			{
				// check if we are adding the same object
				if (_table[pos] == obj)
				{
					return;
				}
				// this should never happen
				assert obj.getObjectId() != _table[pos].getObjectId();
				// if there was no collisions at this slot, and we found a free
				// slot previously - use found slot
				if ((slot >= 0) && (_keys[pos] > 0))
				{
					_keys[slot] |= hashcode; // preserve collision bit
					_table[slot] = obj;
					_count++;
					if (TRACE)
					{
						System.err.println("ht: put obj id="+hashcode+" at slot="+slot);
					}
					if (DEBUG)
					{
						check();
					}
					return;
				}
			}
			
			// set collision bit
			_keys[pos] |= 0x80000000;
			// calculate next slot
			seed += incr;
		} while (++ntry < _table.length);
		if (DEBUG)
		{
			check();
		}
		throw new IllegalStateException();
	}
	
	@Override
	public synchronized void remove(T obj)
	{
		int hashcode = obj.getObjectId();
		assert hashcode > 0;
		int seed = hashcode;
		int incr = 1 + (((seed >> 5) + 1) % (_table.length - 1));
		int ntry = 0;
		do
		{
			int pos = (seed % _table.length) & 0x7FFFFFFF;
			if (_table[pos] == obj)
			{
				// found the object
				_keys[pos] &= 0x80000000; // preserve collision bit
				_table[pos] = null;
				_count--;
				if (TRACE)
				{
					System.err.println("ht: remove obj id="+hashcode+" from slot="+pos);
				}
				if (DEBUG)
				{
					check();
				}
				return;
			}
			// check for collision (if we previously deleted element)
			if ((_table[pos] == null) && (_keys[pos] >= 0)) {
				if (DEBUG)
				{
					check();
				}
				return; //throw new IllegalArgumentException();
			}
			// calculate next slot
			seed += incr;
		} while (++ntry < _table.length);
		if (DEBUG)
		{
			check();
		}
		throw new IllegalStateException();
	}
	
	@Override
	public T get(int id)
	{
		final int size = _table.length;
		if (id <= 0)
		{
			return null;
		}
		if (size <= 11)
		{
			// for small tables linear check is fast
			for (int i=0; i < size; i++)
			{
				if ((_keys[i]&0x7FFFFFFF) == id)
				{
					return _table[i];
				}
			}
			return null;
		}
		int seed = id;
		int incr = 1 + (((seed >> 5) + 1) % (size - 1));
		int ntry = 0;
		do
		{
			int pos = (seed % size) & 0x7FFFFFFF;
			if ((_keys[pos]&0x7FFFFFFF) == id)
			{
				return _table[pos];
			}
			// check for collision (if we previously deleted element)
			if ((_table[pos] == null) && (_keys[pos] >= 0)) {
				return null;
			}
			// calculate next slot
			seed += incr;
		} while (++ntry < size);
		return null;
	}
	
	@Override
	public boolean contains(T obj)
	{
		return get(obj.getObjectId()) != null;
	}
	
	@SuppressWarnings("unchecked")
	private /*already synchronized in put()*/ void expand()
	{
		int newSize = getPrime(_table.length+1);
		L2Object[] newTable = new L2Object[newSize];
		int[] newKeys = new int[newSize];
		
		// over all old entries
		next_entry:
			for (int i=0; i < _table.length; i++)
			{
				L2Object obj = _table[i];
				if (obj == null)
				{
					continue;
				}
				final int hashcode = _keys[i] & 0x7FFFFFFF;
				assert hashcode == obj.getObjectId();
				int seed = hashcode;
				int incr = 1 + (((seed >> 5) + 1) % (newSize - 1));
				int ntry = 0;
				do
				{
					int pos = (seed % newSize) & 0x7FFFFFFF;
					if (newTable[pos] == null)
					{
						assert (newKeys[pos] == 0) && (hashcode != 0);
						// found an empty slot without previous collisions,
						// but use previously found slot
						newKeys[pos] = hashcode;
						newTable[pos] = obj;
						if (TRACE)
						{
							System.err.println("ht: move obj id="+hashcode+" from slot="+i+" to slot="+pos);
						}
						continue next_entry;
					}
					// set collision bit
					newKeys[pos] |= 0x80000000;
					// calculate next slot
					seed += incr;
				} while (++ntry < newSize);
				throw new IllegalStateException();
			}
		_table = (T[])newTable;
		_keys = newKeys;
		if (DEBUG)
		{
			check();
		}
	}
	
	@Override
	public Iterator<T> iterator()
	{
		return new Itr(_table);
	}
	
	class Itr implements Iterator<T>
	{
		private final T[] _array;
		private int _nextIdx;
		private T _nextObj;
		private T _lastRet;
		
		Itr(T[] pArray)
		{
			this._array = pArray;
			for (; _nextIdx < _array.length; _nextIdx++)
			{
				_nextObj = _array[_nextIdx];
				if (_nextObj != null)
				{
					return;
				}
			}
		}
		
		@Override
		public boolean hasNext()
		{
			return _nextObj != null;
		}
		
		@Override
		public T next()
		{
			if (_nextObj == null)
			{
				throw new NoSuchElementException();
			}
			_lastRet = _nextObj;
			for (_nextIdx++; _nextIdx < _array.length; _nextIdx++)
			{
				_nextObj = _array[_nextIdx];
				if (_nextObj != null)
				{
					break;
				}
			}
			if (_nextIdx >= _array.length)
			{
				_nextObj = null;
			}
			return _lastRet;
		}
		@Override
		public void remove()
		{
			if (_lastRet == null)
			{
				throw new IllegalStateException();
			}
			L2ObjectHashMap.this.remove(_lastRet);
		}
	}
}