/*
 * Copyright (c) 2009, 2011, Oracle and/or its affiliates. All rights reserved.
 * Copyright (C) 2014-2020 MicroEJ Corp. - EDC compliance and optimizations.
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 *
 * This code is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 only, as
 * published by the Free Software Foundation.  Oracle designates this
 * particular file as subject to the "Classpath" exception as provided
 * by Oracle in the LICENSE file that accompanied this code.
 *
 * This code 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
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 *
 * You should have received a copy of the GNU General Public License version
 * 2 along with this work; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 *
 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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 * questions.
 */

package java.util;

import ej.annotation.Nullable;

/**
 * This class consists of {@code static} utility methods for operating on objects. These utilities include
 * {@code null}-safe or {@code
 * null}-tolerant methods for computing the hash code of an object, returning a string for an object, and comparing two
 * objects.
 *
 * @since 1.7
 */
public final class Objects {
	private Objects() {
		throw new AssertionError("No java.util.Objects instances for you!");
	}

	/**
	 * Returns {@code true} if the arguments are equal to each other and {@code false} otherwise. Consequently, if both
	 * arguments are {@code null}, {@code true} is returned and if exactly one argument is {@code null}, {@code
	 * false} is returned. Otherwise, equality is determined by using the {@link Object#equals equals} method of the
	 * first argument.
	 *
	 * @param a
	 *            an object
	 * @param b
	 *            an object to be compared with {@code a} for equality
	 * @return {@code true} if the arguments are equal to each other and {@code false} otherwise
	 * @see Object#equals(Object)
	 */
	public static boolean equals(Object a, Object b) {
		return (a == b) || (a != null && a.equals(b));
	}

	/**
	 * Returns {@code true} if the arguments are deeply equal to each other and {@code false} otherwise.
	 *
	 * Two {@code null} values are deeply equal. If both arguments are arrays, the algorithm in
	 * {@link Arrays#deepEquals(Object[], Object[]) Arrays.deepEquals} is used to determine equality. Otherwise,
	 * equality is determined by using the {@link Object#equals equals} method of the first argument.
	 *
	 * @param a
	 *            an object
	 * @param b
	 *            an object to be compared with {@code a} for deep equality
	 * @return {@code true} if the arguments are deeply equal to each other and {@code false} otherwise
	 * @see Arrays#deepEquals(Object[], Object[])
	 * @see Objects#equals(Object, Object)
	 */
	public static boolean deepEquals(Object a, Object b) {
		if (a == b) {
			return true;
		} else if (a == null || b == null) {
			return false;
		} else {
			return Arrays.deepEquals0(a, b);
		}
	}

	/**
	 * Returns the hash code of a non-{@code null} argument and 0 for a {@code null} argument.
	 *
	 * @param o
	 *            an object
	 * @return the hash code of a non-{@code null} argument and 0 for a {@code null} argument
	 * @see Object#hashCode
	 */
	public static int hashCode(Object o) {
		return o != null ? o.hashCode() : 0;
	}

	/**
	 * Generates a hash code for a sequence of input values. The hash code is generated as if all the input values were
	 * placed into an array, and that array were hashed by calling {@link Arrays#hashCode(Object[])}.
	 *
	 * <p>
	 * This method is useful for implementing {@link Object#hashCode()} on objects containing multiple fields. For
	 * example, if an object that has three fields, {@code x}, {@code
	 * y}, and {@code z}, one could write:
	 *
	 * <blockquote>
	 *
	 * <pre>
	 * &#064;Override
	 * public int hashCode() {
	 * 	return Objects.hash(x, y, z);
	 * }
	 * </pre>
	 *
	 * </blockquote>
	 *
	 * <b>Warning: When a single object reference is supplied, the returned value does not equal the hash code of that
	 * object reference.</b> This value can be computed by calling {@link #hashCode(Object)}.
	 *
	 * @param values
	 *            the values to be hashed
	 * @return a hash value of the sequence of input values
	 * @see Arrays#hashCode(Object[])
	 * @see List#hashCode
	 */
	public static int hash(Object... values) {
		return Arrays.hashCode(values);
	}

	/**
	 * Returns the result of calling {@code toString} for a non-{@code
	 * null} argument and {@code "null"} for a {@code null} argument.
	 *
	 * @param o
	 *            an object
	 * @return the result of calling {@code toString} for a non-{@code
	 * null} argument and {@code "null"} for a {@code null} argument
	 * @see Object#toString
	 * @see String#valueOf(Object)
	 */
	public static String toString(Object o) {
		return String.valueOf(o);
	}

	/**
	 * Returns the result of calling {@code toString} on the first argument if the first argument is not {@code null}
	 * and returns the second argument otherwise.
	 *
	 * @param o
	 *            an object
	 * @param nullDefault
	 *            string to return if the first argument is {@code null}
	 * @return the result of calling {@code toString} on the first argument if it is not {@code null} and the second
	 *         argument otherwise.
	 * @see Objects#toString(Object)
	 */
	public static String toString(@Nullable Object o, String nullDefault) {
		return (o != null) ? o.toString() : nullDefault;
	}

	/**
	 * Returns 0 if the arguments are identical and {@code
	 * c.compare(a, b)} otherwise. Consequently, if both arguments are {@code null} 0 is returned.
	 *
	 * <p>
	 * Note that if one of the arguments is {@code null}, a {@code
	 * NullPointerException} may or may not be thrown depending on what ordering policy, if any, the {@link Comparator
	 * Comparator} chooses to have for {@code null} values.
	 *
	 * @param <T>
	 *            the type of the objects being compared
	 * @param a
	 *            an object
	 * @param b
	 *            an object to be compared with {@code a}
	 * @param c
	 *            the {@code Comparator} to compare the first two arguments
	 * @return 0 if the arguments are identical and {@code
	 * c.compare(a, b)} otherwise.
	 * @see Comparable
	 * @see Comparator
	 */
	public static <T> int compare(T a, T b, Comparator<? super T> c) {
		return (a == b) ? 0 : c.compare(a, b);
	}

	/**
	 * Checks that the specified object reference is not {@code null}. This method is designed primarily for doing
	 * parameter validation in methods and constructors, as demonstrated below: <blockquote>
	 *
	 * <pre>
	 * public Foo(Bar bar) {
	 * 	this.bar = Objects.requireNonNull(bar);
	 * }
	 * </pre>
	 *
	 * </blockquote>
	 *
	 * @param obj
	 *            the object reference to check for nullity
	 * @param <T>
	 *            the type of the reference
	 * @return {@code obj} if not {@code null}
	 * @throws NullPointerException
	 *             if {@code obj} is {@code null}
	 */
	public static <T> T requireNonNull(@Nullable T obj) {
		if (obj == null) {
			throw new NullPointerException();
		}
		return obj;
	}

	/**
	 * Checks that the specified object reference is not {@code null} and throws a customized
	 * {@link NullPointerException} if it is. This method is designed primarily for doing parameter validation in
	 * methods and constructors with multiple parameters, as demonstrated below: <blockquote>
	 *
	 * <pre>
	 * public Foo(Bar bar, Baz baz) {
	 * 	this.bar = Objects.requireNonNull(bar, "bar must not be null");
	 * 	this.baz = Objects.requireNonNull(baz, "baz must not be null");
	 * }
	 * </pre>
	 *
	 * </blockquote>
	 *
	 * @param obj
	 *            the object reference to check for nullity
	 * @param message
	 *            detail message to be used in the event that a {@code
	 *                NullPointerException} is thrown
	 * @param <T>
	 *            the type of the reference
	 * @return {@code obj} if not {@code null}
	 * @throws NullPointerException
	 *             if {@code obj} is {@code null}
	 */
	public static <T> T requireNonNull(@Nullable T obj, String message) {
		if (obj == null) {
			throw new NullPointerException(message);
		}
		return obj;
	}
}