/*

 * 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.

 *

 * 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

 * or visit www.oracle.com if you need additional information or have any

 * questions.

 */

/*

 * This file is available under and governed by the GNU General Public

 * License version 2 only, as published by the Free Software Foundation.

 * However, the following notice accompanied the original version of this

 * file:

 *

 * Written by Martin Buchholz with assistance from members of JCP

 * JSR-166 Expert Group and released to the public domain, as

 * explained at http://creativecommons.org/publicdomain/zero/1.0/

 */

/*

 * @test

 * @modules java.base/java.util:open

 * @run testng WhiteBox

 * @summary White box tests of implementation details

 */

import static org.testng.Assert.*;

import org.testng.annotations.Test;

import java.io.ByteArrayInputStream;

import java.io.ByteArrayOutputStream;

import java.io.ObjectInputStream;

import java.io.ObjectOutputStream;

import java.lang.invoke.MethodHandles;

import java.lang.invoke.VarHandle;

import java.util.ArrayDeque;

import java.util.concurrent.ThreadLocalRandom;

@Test

public class WhiteBox {

    final ThreadLocalRandom rnd = ThreadLocalRandom.current();

    final VarHandle ELEMENTS, HEAD, TAIL;

    WhiteBox() throws ReflectiveOperationException {

        Class<?> klazz = ArrayDeque.class;

        MethodHandles.Lookup lookup

            = MethodHandles.privateLookupIn(klazz, MethodHandles.lookup());

        ELEMENTS = lookup.findVarHandle(klazz, "elements", Object[].class);

        HEAD = lookup.findVarHandle(klazz, "head", int.class);

        TAIL = lookup.findVarHandle(klazz, "tail", int.class);

    }

    Object[] elements(ArrayDeque d) { return (Object[]) ELEMENTS.get(d); }

    int head(ArrayDeque d) { return (int) HEAD.get(d); }

    int tail(ArrayDeque d) { return (int) TAIL.get(d); }

    void checkCapacity(ArrayDeque d, int capacity) {

        assertTrue(d.isEmpty());

        assertEquals(0, head(d));

        assertEquals(0, tail(d));

        Object[] initialElements = elements(d);

        assertInvariants(d);

        for (int i = capacity; i--> 0; ) {

            d.add(rnd.nextInt(42));

            assertSame(elements(d), initialElements);

            assertInvariants(d);

        }

        d.add(rnd.nextInt(42));

        assertNotSame(elements(d), initialElements);

        assertInvariants(d);

    }

    @Test

    public void defaultConstructor() {

        checkCapacity(new ArrayDeque(), 16);

    }

    @Test

    public void shouldNotResizeWhenInitialCapacityProvided() {

        int initialCapacity = rnd.nextInt(20);

        checkCapacity(new ArrayDeque(initialCapacity), initialCapacity);

    }

    byte[] serialBytes(Object o) {

        try {

            ByteArrayOutputStream bos = new ByteArrayOutputStream();

            ObjectOutputStream oos = new ObjectOutputStream(bos);

            oos.writeObject(o);

            oos.flush();

            oos.close();

            return bos.toByteArray();

        } catch (Exception fail) {

            throw new AssertionError(fail);

        }

    }

    @SuppressWarnings("unchecked")

    <T> T serialClone(T o) {

        try {

            ObjectInputStream ois = new ObjectInputStream

                (new ByteArrayInputStream(serialBytes(o)));

            T clone = (T) ois.readObject();

            assertNotSame(o, clone);

            assertSame(o.getClass(), clone.getClass());

            return clone;

        } catch (Exception fail) {

            throw new AssertionError(fail);

        }

    }

    @Test

    public void testSerialization() {

        ArrayDeque[] ds = { new ArrayDeque(), new ArrayDeque(rnd.nextInt(20)) };

        for (ArrayDeque d : ds) {

            if (rnd.nextBoolean()) d.add(99);

            ArrayDeque clone = serialClone(d);

            assertInvariants(clone);

            assertNotSame(elements(d), elements(clone));

            assertEquals(d, clone);

        }

    }

    /** Checks conditions which should always be true. */

    void assertInvariants(ArrayDeque d) {

        final Object[] elements = elements(d);

        final int head = head(d);

        final int tail = tail(d);

        final int capacity = elements.length;

        assertTrue(0 <= head && head < capacity);

        assertTrue(0 <= tail && tail < capacity);

        assertTrue(capacity > 0);

        assertTrue(d.size() < capacity);

        assertTrue((head == tail) ^ (elements[head] != null));

        assertNull(elements[tail]);

        assertTrue((head == tail) ^ (elements[Math.floorMod(tail - 1, capacity)] != null));

    }

}