/*
 * LinShare is an open source filesharing software, part of the LinPKI software
 * suite, developed by Linagora.
 * 
 * Copyright (C) 2015 LINAGORA
 * 
 * This program is free software: you can redistribute it and/or modify it under
 * the terms of the GNU Affero General Public License as published by the Free
 * Software Foundation, either version 3 of the License, or (at your option) any
 * later version, provided you comply with the Additional Terms applicable for
 * LinShare software by Linagora pursuant to Section 7 of the GNU Affero General
 * Public License, subsections (b), (c), and (e), pursuant to which you must
 * notably (i) retain the display of the “LinShare™” trademark/logo at the top
 * of the interface window, the display of the “You are using the Open Source
 * and free version of LinShare™, powered by Linagora © 2009–2015. Contribute to
 * Linshare R&D by subscribing to an Enterprise offer!” infobox and in the
 * e-mails sent with the Program, (ii) retain all hypertext links between
 * LinShare and linshare.org, between linagora.com and Linagora, and (iii)
 * refrain from infringing Linagora intellectual property rights over its
 * trademarks and commercial brands. Other Additional Terms apply, see
 * <http://www.linagora.com/licenses/> for more details.
 * 
 * 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 Affero General Public License for more
 * details.
 * 
 * You should have received a copy of the GNU Affero General Public License and
 * its applicable Additional Terms for LinShare along with this program. If not,
 * see <http://www.gnu.org/licenses/> for the GNU Affero General Public License
 * version 3 and <http://www.linagora.com/licenses/> for the Additional Terms
 * applicable to LinShare software.
 */
package org.linagora.linshare.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>
 * 
 * Taken from http://www.javapractices.com/topic/TopicAction.do?Id=28
 */
public final class HashCodeUtil {

	/**
	 * An initial value for a <code>hashCode</code>, to which is added
	 * contributions from fields. Using a non-zero value decreases collisons of
	 * <code>hashCode</code> values.
	 */
	public static final int SEED = 23;

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

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

	/**
	 * longs.
	 */
	public static int hash(int aSeed, long aLong) {
		System.out.println("long...");
		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();
	}
}