/*
 * Lokomo OneCMDB - An Open Source Software for Configuration
 * Management of Datacenter Resources
 *
 * Copyright (C) 2006 Lokomo Systems AB
 *
 * 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.
 *
 * 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, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
 * 02110-1301 USA.
 * 
 * Lokomo Systems AB can be contacted via e-mail: info@lokomo.com or via
 * paper mail: Lokomo Systems AB, Sv�rdv�gen 27, SE-182 33
 * Danderyd, Sweden.
 *
 */
package org.onecmdb.core.utils;

import java.lang.reflect.Array;

/**
 * Collected methods which allow easy implementation of <code>hashCode</code>.
 * 
 * Example use case:
 * 
 * <pre>
 * public int hashCode() {
 * 	int result = HashCodeUtil.SEED;
 * 	//collect the contributions of various fields
 * 	result = HashCodeUtil.hash(result, fPrimitive);
 * 	result = HashCodeUtil.hash(result, fObject);
 * 	result = HashCodeUtil.hash(result, fArray);
 * 	return result;
 * }
 * </pre>
 */
public final class HashCodeUtil {

    /** hidden */
    private HashCodeUtil() {};
    
    
	/**
	 * An initial value for a <code>hashCode</code>, to which is added
	 * contributions from fields. Using a non-zero value decreases collisions of
	 * <code>hashCode</code> values.
	 */
	public static final int SEED = 23;

	/**
	 * booleans.
	 */
	public static int hash(int aSeed, boolean aBoolean) {
		return firstTerm(aSeed) + (aBoolean ? 1 : 0);
	}

	/**
	 * chars.
	 */
	public static int hash(int aSeed, char aChar) {
		return firstTerm(aSeed) + (int) aChar;
	}

	/**
	 * ints.
	 */
	public static int hash(int aSeed, int aInt) {
		/*
		 * Implementation Note: Note that byte and short are handled by this
		 * method, through implicit conversion.
		 */
		return firstTerm(aSeed) + aInt;
	}

	/**
	 * longs.
	 */
	public static int hash(int aSeed, long aLong) {
		return firstTerm(aSeed) + (int) (aLong ^ (aLong >>> 32));
	}

	/**
	 * floats.
	 */
	public static int hash(int aSeed, float aFloat) {
		return hash(aSeed, Float.floatToIntBits(aFloat));
	}

	/**
	 * doubles.
	 */
	public static int hash(int aSeed, double aDouble) {
		return hash(aSeed, Double.doubleToLongBits(aDouble));
	}

	/**
	 * <code>aObject</code> is a possibly-null object field, and possibly an
	 * array.
	 * 
	 * If <code>aObject</code> is an array, then each element may be a
	 * primitive or a possibly-null object.
	 */
	public static int hash(int aSeed, Object aObject) {
		int result = aSeed;
		if (aObject == null) {
			result = hash(result, 0);
		} else if (!isArray(aObject)) {
			result = hash(result, aObject.hashCode());
		} else {
			int length = Array.getLength(aObject);
			for (int idx = 0; idx < length; ++idx) {
				Object item = Array.get(aObject, idx);
				// recursive call!
				result = hash(result, item);
			}
		}
		return result;
	}

	// / PRIVATE ///
	private static final int fODD_PRIME_NUMBER = 37;

	private static int firstTerm(int aSeed) {
		return fODD_PRIME_NUMBER * aSeed;
	}

	private static boolean isArray(Object aObject) {
		return aObject.getClass().isArray();
	}
}