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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.seqno;

import org.opensearch.common.annotation.PublicApi;
import org.opensearch.core.common.io.stream.StreamInput;
import org.opensearch.core.common.io.stream.StreamOutput;
import org.opensearch.core.common.io.stream.Writeable;
import org.opensearch.core.xcontent.ToXContentFragment;
import org.opensearch.core.xcontent.XContentBuilder;

import java.io.IOException;
import java.util.Objects;

/**
 * Sequence number statistics
 *
 * @opensearch.api
 */
@PublicApi(since = "1.0.0")
public class SeqNoStats implements ToXContentFragment, Writeable {

    private static final String SEQ_NO = "seq_no";
    private static final String MAX_SEQ_NO = "max_seq_no";
    private static final String LOCAL_CHECKPOINT = "local_checkpoint";
    private static final String GLOBAL_CHECKPOINT = "global_checkpoint";

    private final long maxSeqNo;
    private final long localCheckpoint;
    private final long globalCheckpoint;

    public SeqNoStats(long maxSeqNo, long localCheckpoint, long globalCheckpoint) {
        assert localCheckpoint <= maxSeqNo : "local checkpoint [" + localCheckpoint + "] is above maximum seq no [" + maxSeqNo + "]";
        // note that the global checkpoint can be higher from both maxSeqNo and localCheckpoint
        // as we use this stats object to describe lucene commits as well as live statistic.
        this.maxSeqNo = maxSeqNo;
        this.localCheckpoint = localCheckpoint;
        this.globalCheckpoint = globalCheckpoint;
    }

    public SeqNoStats(StreamInput in) throws IOException {
        this(in.readZLong(), in.readZLong(), in.readZLong());
    }

    /** the maximum sequence number seen so far */
    public long getMaxSeqNo() {
        return maxSeqNo;
    }

    /** the maximum sequence number for which all previous operations (including) have been persisted */
    public long getLocalCheckpoint() {
        return localCheckpoint;
    }

    public long getGlobalCheckpoint() {
        return globalCheckpoint;
    }

    @Override
    public void writeTo(StreamOutput out) throws IOException {
        out.writeZLong(maxSeqNo);
        out.writeZLong(localCheckpoint);
        out.writeZLong(globalCheckpoint);
    }

    @Override
    public XContentBuilder toXContent(XContentBuilder builder, Params params) throws IOException {
        builder.startObject(SEQ_NO);
        builder.field(MAX_SEQ_NO, maxSeqNo);
        builder.field(LOCAL_CHECKPOINT, localCheckpoint);
        builder.field(GLOBAL_CHECKPOINT, globalCheckpoint);
        builder.endObject();
        return builder;
    }

    @Override
    public boolean equals(Object o) {
        if (this == o) return true;
        if (o == null || getClass() != o.getClass()) return false;
        final SeqNoStats that = (SeqNoStats) o;
        return maxSeqNo == that.maxSeqNo && localCheckpoint == that.localCheckpoint && globalCheckpoint == that.globalCheckpoint;
    }

    @Override
    public int hashCode() {
        return Objects.hash(maxSeqNo, localCheckpoint, globalCheckpoint);
    }

    @Override
    public String toString() {
        return "SeqNoStats{"
            + "maxSeqNo="
            + maxSeqNo
            + ", localCheckpoint="
            + localCheckpoint
            + ", globalCheckpoint="
            + globalCheckpoint
            + '}';
    }
}