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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.index.engine;

import org.apache.lucene.util.Accountable;
import org.apache.lucene.util.RamUsageEstimator;
import org.opensearch.common.Nullable;
import org.opensearch.index.translog.Translog;

import java.util.Collection;
import java.util.Collections;

/**
 * Represents the version of a document in the index
 *
 * @opensearch.internal
 */
abstract class VersionValue implements Accountable {

    private static final long BASE_RAM_BYTES_USED = RamUsageEstimator.shallowSizeOfInstance(VersionValue.class);

    /** the version of the document. used for versioned indexed operations and as a BWC layer, where no seq# are set yet */
    final long version;

    /** the seq number of the operation that last changed the associated uuid */
    final long seqNo;
    /** the term of the operation that last changed the associated uuid */
    final long term;

    VersionValue(long version, long seqNo, long term) {
        this.version = version;
        this.seqNo = seqNo;
        this.term = term;
    }

    public boolean isDelete() {
        return false;
    }

    @Override
    public long ramBytesUsed() {
        return BASE_RAM_BYTES_USED;
    }

    @Override
    public Collection getChildResources() {
        return Collections.emptyList();
    }

    @Override
    public boolean equals(Object o) {
        if (this == o) return true;
        if (o == null || getClass() != o.getClass()) return false;

        VersionValue that = (VersionValue) o;

        if (version != that.version) return false;
        if (seqNo != that.seqNo) return false;
        return term == that.term;
    }

    @Override
    public int hashCode() {
        int result = (int) (version ^ (version >>> 32));
        result = 31 * result + (int) (seqNo ^ (seqNo >>> 32));
        result = 31 * result + (int) (term ^ (term >>> 32));
        return result;
    }

    @Override
    public String toString() {
        return "VersionValue{" + "version=" + version + ", seqNo=" + seqNo + ", term=" + term + '}';
    }

    /**
     * Returns the translog location for this version value or null. This is optional and might not be tracked all the time.
     */
    @Nullable
    public Translog.Location getLocation() {
        return null;
    }
}