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/**
 * The MIT License
 *
 * Copyright (C) 2015 Asterios Raptis
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy of this software and
 * associated documentation files (the "Software"), to deal in the Software without restriction,
 * including without limitation the rights to use, copy, modify, merge, publish, distribute,
 * sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in all copies or
 * substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT
 * NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
 * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM,
 * DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
 */
package de.alpharogroup.evaluate.object.checkers;

import java.util.Optional;

import de.alpharogroup.evaluate.object.api.ContractViolation;
import de.alpharogroup.evaluate.object.enums.HashcodeContractViolation;
import lombok.experimental.UtilityClass;

/**
 * The class {@link HashcodeCheck} provides algorithms for check the
 * hashcode
 * contract of an given object.
 */
@UtilityClass
public final class HashcodeCheck
{

	/**
	 * Checks consistency of the given object, that means according to {@link Object#hashCode()}
	 * that this method should evaluate the following contract condition:
	 * 
	 * Whenever it is invoked on the same object more than once during an execution of a Java
	 * application, the {@code hashCode} method must consistently return the same integer, provided
	 * no information used in {@code equals} comparisons on the object is modified. This integer
	 * need not remain consistent from one execution of an application to another execution of the
	 * same application.
	 * 
	 *
	 * Note: The upper list is taken from the javadoc from {@link Object#hashCode()}
	 *
	 * @param 
	 *            the generic type
	 * @param object
	 *            the object
	 * @return an empty {@link Optional} if no violation occurred or an {@link Optional} with the
	 *         specific violation type
	 */
	public static  Optional consistency(T object)
	{
		if (object == null)
		{
			return Optional.of(HashcodeContractViolation.CONSISTENCY_NULL_ARGUMENT);
		}
		boolean equalHashcode = object.hashCode() == object.hashCode();
		return equalHashcode
			? Optional.empty()
			: Optional.of(HashcodeContractViolation.CONSISTENCY);
	}

	/**
	 * Checks equality of hash code from the given objects that should be equal(if not an
	 * {@link IllegalArgumentException} will be thrown), that means according to
	 * {@link Object#hashCode()} that this method should evaluate the following contract condition:
	 * 
	 * If two objects are equal according to the {@code equals(Object)} method, then calling the
	 * {@code hashCode} method on each of the two objects must produce the same integer result.
	 * 
	 *
	 * @param 
	 *            the generic type
	 * @param object
	 *            the object
	 * @param anotherObject
	 *            the another object
	 * @return an empty {@link Optional} if no violation occurred or an {@link Optional} with the
	 *         specific violation type
	 */
	public static  Optional equality(T object, T anotherObject)
	{
		if (object == null)
		{
			return Optional.of(HashcodeContractViolation.EQAUALITY_NULL_ARGUMENT);
		}
		if (object.equals(anotherObject))
		{
			boolean equalHashcode = object.hashCode() == anotherObject.hashCode();
			return equalHashcode
				? Optional.empty()
				: Optional.of(HashcodeContractViolation.EQAUALITY);
		}
		return Optional.of(HashcodeContractViolation.EQAUALITY);
	}

	/**
	 * Checks unequality of hash code from the given objects that should be unequal, that means
	 * according to {@link Object#hashCode()} that this method should evaluate the following
	 * contract condition:
	 * 
	 * It is not required that if two objects are unequal according to the
	 * {@link java.lang.Object#equals(java.lang.Object)} method, then calling the {@code hashCode}
	 * method on each of the two objects must produce distinct integer results. However, the
	 * programmer should be aware that producing distinct integer results for unequal objects may
	 * improve the performance of hash tables.
	 * 
	 *
	 * @param 
	 *            the generic type
	 * @param object
	 *            the object
	 * @param anotherObject
	 *            the another object
	 * @return an empty {@link Optional} if no violation occurred or an {@link Optional} with the
	 *         specific violation type
	 */
	public static  Optional unequality(T object, T anotherObject)
	{
		if (object == null)
		{
			return Optional.of(HashcodeContractViolation.UNEQAUALITY_NULL_ARGUMENT);
		}
		if (!object.equals(anotherObject))
		{
			if (anotherObject == null)
			{
				return Optional.empty();
			}
			boolean unequalHashcode = object.hashCode() != anotherObject.hashCode();
			if (unequalHashcode)
			{
				return Optional.empty();
			}
		}
		return Optional.of(HashcodeContractViolation.UNEQAUALITY);
	}

}