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/*
 * SPDX-License-Identifier: Apache-2.0
 *
 * The OpenSearch Contributors require contributions made to
 * this file be licensed under the Apache-2.0 license or a
 * compatible open source license.
 */

/*
 * Licensed to Elasticsearch under one or more contributor
 * license agreements. See the NOTICE file distributed with
 * this work for additional information regarding copyright
 * ownership. Elasticsearch licenses this file to you under
 * the Apache License, Version 2.0 (the "License"); you may
 * not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *    http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing,
 * software distributed under the License is distributed on an
 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
 * KIND, either express or implied.  See the License for the
 * specific language governing permissions and limitations
 * under the License.
 */

/*
 * Modifications Copyright OpenSearch Contributors. See
 * GitHub history for details.
 */

package org.opensearch.nio;

import org.opensearch.common.util.concurrent.AbstractRefCounted;

import java.io.Closeable;
import java.nio.ByteBuffer;

public class Page implements Closeable {

    private final ByteBuffer byteBuffer;
    // This is reference counted as some implementations want to retain the byte pages by calling
    // duplicate. With reference counting we can increment the reference count, return a new page,
    // and safely close the pages independently. The closeable will not be called until each page is
    // released.
    private final RefCountedCloseable refCountedCloseable;

    public Page(ByteBuffer byteBuffer) {
        this(byteBuffer, () -> {});
    }

    public Page(ByteBuffer byteBuffer, Runnable closeable) {
        this(byteBuffer, new RefCountedCloseable(closeable));
    }

    private Page(ByteBuffer byteBuffer, RefCountedCloseable refCountedCloseable) {
        this.byteBuffer = byteBuffer;
        this.refCountedCloseable = refCountedCloseable;
    }

    /**
     * Duplicates this page and increments the reference count. The new page must be closed independently
     * of the original page.
     *
     * @return the new page
     */
    public Page duplicate() {
        refCountedCloseable.incRef();
        return new Page(byteBuffer.duplicate(), refCountedCloseable);
    }

    /**
     * Returns the {@link ByteBuffer} for this page. Modifications to the limits, positions, etc of the
     * buffer will also mutate this page. Call {@link ByteBuffer#duplicate()} to avoid mutating the page.
     *
     * @return the byte buffer
     */
    public ByteBuffer byteBuffer() {
        return byteBuffer;
    }

    @Override
    public void close() {
        refCountedCloseable.decRef();
    }

    private static class RefCountedCloseable extends AbstractRefCounted {

        private final Runnable closeable;

        private RefCountedCloseable(Runnable closeable) {
            super("byte array page");
            this.closeable = closeable;
        }

        @Override
        protected void closeInternal() {
            closeable.run();
        }
    }
}