/*******************************************************************************
 * Copyright (c) 2000, 2007 IBM Corporation and others.
 * All rights reserved. This program and the accompanying materials
 * are made available under the terms of the Eclipse Public License v1.0
 * which accompanies this distribution, and is available at
 * http://www.eclipse.org/legal/epl-v10.html
 *
 
 *******************************************************************************/
package org.eclipse.dltk.compiler.util;

/**
 * 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) {
		this.elementSize = 0;
		this.threshold = size; // size represents the expected number of
								// elements
		int extraRoom = (int) (size * 1.5f);
		if (this.threshold == extraRoom)
			extraRoom++;
		this.keyTable = new Object[extraRoom];
		this.valueTable = new Object[extraRoom];
	}

	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 = keyTable.length; i < l; i++)
				if (keyTable[i] != null && 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 Object 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--;
				Object oldValue = valueTable[index];
				keyTable[index] = null;
				valueTable[index] = null;
				if (keyTable[index + 1 == length ? 0 : index + 1] != null)
					rehash(); // only needed if a possible collision existed
				return oldValue;
			}
			if (++index == length)
				index = 0;
		}
		return null;
	}

	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;
	}
}
