/*******************************************************************************
 * Copyright (c) 2000, 2003 IBM Corporation and others.
 * All rights reserved. This program and the accompanying materials 
 * are made available under the terms of the Common Public License v1.0
 * which accompanies this distribution, and is available at
 * http://www.eclipse.org/legal/cpl-v10.html
 * 
 * Contributors:
 *     IBM Corporation - initial API and implementation
 *******************************************************************************/
package org.eclipse.cdt.internal.core.search;

/**
 * A simple lookup table is a non-synchronized Hashtable, whose keys
 * and values are Objects. It also uses linear probing to resolve collisions
 * rather than a linked list of hash table entries.
 */
public final class SimpleLookupTable implements Cloneable {
	
	// to avoid using Enumerations, walk the individual tables skipping nulls
	public Object[] keyTable;
	public Object[] valueTable;
	public int elementSize; // number of elements in the table
	public int threshold;
	
	public SimpleLookupTable() {
		this(13);
	}
	
	public SimpleLookupTable(int size) {
		if (size < 3) size = 3;
		this.elementSize = 0;
		this.threshold = size + 1; // size is the expected number of elements
		int tableLength = 2 * size + 1;
		this.keyTable = new Object[tableLength];
		this.valueTable = new Object[tableLength];
	}
	
	public Object clone() throws CloneNotSupportedException {
		SimpleLookupTable result = (SimpleLookupTable) super.clone();
		result.elementSize = this.elementSize;
		result.threshold = this.threshold;
	
		int length = this.keyTable.length;
		result.keyTable = new Object[length];
		System.arraycopy(this.keyTable, 0, result.keyTable, 0, length);
	
		length = this.valueTable.length;
		result.valueTable = new Object[length];
		System.arraycopy(this.valueTable, 0, result.valueTable, 0, length);
		return result;
	}
	
	public boolean containsKey(Object key) {
		int length = keyTable.length;
		int index = (key.hashCode() & 0x7FFFFFFF) % length;
		Object currentKey;
		while ((currentKey = keyTable[index]) != null) {
			if (currentKey.equals(key)) return true;
			if (++index == length) index = 0;
		}
		return false;
	}
	
	public Object get(Object key) {
		int length = keyTable.length;
		int index = (key.hashCode() & 0x7FFFFFFF) % length;
		Object currentKey;
		while ((currentKey = keyTable[index]) != null) {
			if (currentKey.equals(key)) return valueTable[index];
			if (++index == length) index = 0;
		}
		return null;
	}
	
	public Object keyForValue(Object valueToMatch) {
		if (valueToMatch != null)
			for (int i = 0, l = valueTable.length; i < l; i++)
				if (valueToMatch.equals(valueTable[i]))
					return keyTable[i];
		return null;
	}
	
	public Object put(Object key, Object value) {
		int length = keyTable.length;
		int index = (key.hashCode() & 0x7FFFFFFF) % length;
		Object currentKey;
		while ((currentKey = keyTable[index]) != null) {
			if (currentKey.equals(key)) return valueTable[index] = value;
			if (++index == length) index = 0;
		}
		keyTable[index] = key;
		valueTable[index] = value;
	
		// assumes the threshold is never equal to the size of the table
		if (++elementSize > threshold) rehash();
		return value;
	}
	
	public void removeKey(Object key) {
		int length = keyTable.length;
		int index = (key.hashCode() & 0x7FFFFFFF) % length;
		Object currentKey;
		while ((currentKey = keyTable[index]) != null) {
			if (currentKey.equals(key)) {
				elementSize--;
				keyTable[index] = null;
				valueTable[index] = null;
				if (keyTable[index + 1 == length ? 0 : index + 1] != null)
					rehash(); // only needed if a possible collision existed
				return;
			}
			if (++index == length) index = 0;
		}
	}
	
	public void removeValue(Object valueToRemove) {
		boolean rehash = false;
		for (int i = 0, l = valueTable.length; i < l; i++) {
			Object value = valueTable[i];
			if (value != null && value.equals(valueToRemove)) {
				elementSize--;
				keyTable[i] = null;
				valueTable[i] = null;
				if (!rehash && keyTable[i + 1 == l ? 0 : i + 1] != null)
					rehash = true; // only needed if a possible collision existed
			}
		}
		if (rehash) rehash();
	}
	
	private void rehash() {
		SimpleLookupTable newLookupTable = new SimpleLookupTable(elementSize * 2); // double the number of expected elements
		Object currentKey;
		for (int i = keyTable.length; --i >= 0;)
			if ((currentKey = keyTable[i]) != null)
				newLookupTable.put(currentKey, valueTable[i]);
	
		this.keyTable = newLookupTable.keyTable;
		this.valueTable = newLookupTable.valueTable;
		this.elementSize = newLookupTable.elementSize;
		this.threshold = newLookupTable.threshold;
	}
	
	public String toString() {
		String s = ""; //$NON-NLS-1$
		Object object;
		for (int i = 0, l = valueTable.length; i < l; i++)
			if ((object = valueTable[i]) != null)
				s += keyTable[i].toString() + " -> " + object.toString() + "\n"; 	//$NON-NLS-2$ //$NON-NLS-1$
		return s;
	}
}