/*
 * 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.shard;

import org.apache.lucene.index.IndexCommit;
import org.apache.lucene.store.Directory;
import org.apache.lucene.store.FilterDirectory;
import org.apache.lucene.store.IOContext;
import org.apache.lucene.store.IndexOutput;
import org.apache.lucene.store.Lock;
import org.apache.lucene.store.NoLockFactory;
import org.opensearch.cluster.metadata.IndexMetadata;
import org.opensearch.common.concurrent.GatedCloseable;
import org.opensearch.core.index.Index;
import org.opensearch.index.engine.Engine;
import org.opensearch.index.store.Store;

import java.io.Closeable;
import java.io.IOException;
import java.util.Collection;
import java.util.Set;
import java.util.concurrent.atomic.AtomicBoolean;

/**
 * A shard snapshot stored locally
 *
 * @opensearch.internal
 */
final class LocalShardSnapshot implements Closeable {
    private final IndexShard shard;
    private final Store store;
    private final GatedCloseable<IndexCommit> wrappedIndexCommit;
    private final AtomicBoolean closed = new AtomicBoolean(false);

    LocalShardSnapshot(IndexShard shard) {
        this.shard = shard;
        store = shard.store();
        store.incRef();
        boolean success = false;
        try {
            wrappedIndexCommit = shard.acquireLastIndexCommit(true);
            success = true;
        } finally {
            if (success == false) {
                store.decRef();
            }
        }
    }

    Index getIndex() {
        return shard.indexSettings().getIndex();
    }

    long maxSeqNo() {
        return shard.getEngine().getSeqNoStats(-1).getMaxSeqNo();
    }

    long maxUnsafeAutoIdTimestamp() {
        return Long.parseLong(shard.getEngine().commitStats().getUserData().get(Engine.MAX_UNSAFE_AUTO_ID_TIMESTAMP_COMMIT_ID));
    }

    Directory getSnapshotDirectory() {
        /* this directory will not be used for anything else but reading / copying files to another directory
         * we prevent all write operations on this directory with UOE - nobody should close it either. */
        return new FilterDirectory(store.directory()) {
            @Override
            public String[] listAll() throws IOException {
                Collection<String> fileNames = wrappedIndexCommit.get().getFileNames();
                final String[] fileNameArray = fileNames.toArray(new String[0]);
                return fileNameArray;
            }

            @Override
            public void deleteFile(String name) throws IOException {
                throw new UnsupportedOperationException("this directory is read-only");
            }

            @Override
            public void sync(Collection<String> names) throws IOException {
                throw new UnsupportedOperationException("this directory is read-only");
            }

            @Override
            public void rename(String source, String dest) throws IOException {
                throw new UnsupportedOperationException("this directory is read-only");
            }

            @Override
            public IndexOutput createOutput(String name, IOContext context) throws IOException {
                throw new UnsupportedOperationException("this directory is read-only");
            }

            @Override
            public IndexOutput createTempOutput(String prefix, String suffix, IOContext context) throws IOException {
                throw new UnsupportedOperationException("this directory is read-only");
            }

            @Override
            public Lock obtainLock(String name) throws IOException {
                /* we do explicitly a no-lock instance since we hold an index commit from a SnapshotDeletionPolicy so we
                 * can we certain that nobody messes with the files on disk. We also hold a ref on the store which means
                 * no external source will delete files either.*/
                return NoLockFactory.INSTANCE.obtainLock(in, name);
            }

            @Override
            public void close() throws IOException {
                throw new UnsupportedOperationException("nobody should close this directory wrapper");
            }

            // temporary override until LUCENE-8735 is integrated
            @Override
            public Set<String> getPendingDeletions() throws IOException {
                return in.getPendingDeletions();
            }
        };
    }

    @Override
    public void close() throws IOException {
        if (closed.compareAndSet(false, true)) {
            try {
                wrappedIndexCommit.close();
            } finally {
                store.decRef();
            }
        }
    }

    IndexMetadata getIndexMetadata() {
        return shard.indexSettings.getIndexMetadata();
    }

    @Override
    public String toString() {
        return "local_shard_snapshot:[" + shard.shardId() + " indexCommit: " + wrappedIndexCommit + "]";
    }
}