IndexMetadata.java

/*
 * 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.cluster.metadata;

import org.opensearch.LegacyESVersion;
import org.opensearch.Version;
import org.opensearch.action.admin.indices.rollover.RolloverInfo;
import org.opensearch.action.support.ActiveShardCount;
import org.opensearch.cluster.Diff;
import org.opensearch.cluster.Diffable;
import org.opensearch.cluster.DiffableUtils;
import org.opensearch.cluster.block.ClusterBlock;
import org.opensearch.cluster.block.ClusterBlockLevel;
import org.opensearch.cluster.node.DiscoveryNodeFilters;
import org.opensearch.cluster.routing.allocation.IndexMetadataUpdater;
import org.opensearch.cluster.routing.allocation.decider.ShardsLimitAllocationDecider;
import org.opensearch.common.Nullable;
import org.opensearch.common.annotation.PublicApi;
import org.opensearch.common.collect.MapBuilder;
import org.opensearch.common.compress.CompressedXContent;
import org.opensearch.common.settings.Setting;
import org.opensearch.common.settings.Setting.Property;
import org.opensearch.common.settings.Settings;
import org.opensearch.common.xcontent.XContentHelper;
import org.opensearch.core.Assertions;
import org.opensearch.core.common.Strings;
import org.opensearch.core.common.io.stream.StreamInput;
import org.opensearch.core.common.io.stream.StreamOutput;
import org.opensearch.core.common.io.stream.VerifiableWriteable;
import org.opensearch.core.common.io.stream.Writeable;
import org.opensearch.core.index.Index;
import org.opensearch.core.index.shard.ShardId;
import org.opensearch.core.rest.RestStatus;
import org.opensearch.core.xcontent.MediaTypeRegistry;
import org.opensearch.core.xcontent.ToXContent;
import org.opensearch.core.xcontent.ToXContentFragment;
import org.opensearch.core.xcontent.XContentBuilder;
import org.opensearch.core.xcontent.XContentParser;
import org.opensearch.gateway.MetadataStateFormat;
import org.opensearch.index.IndexModule;
import org.opensearch.index.mapper.MapperService;
import org.opensearch.index.seqno.SequenceNumbers;
import org.opensearch.index.translog.BufferedChecksumStreamOutput;
import org.opensearch.indices.replication.SegmentReplicationSource;
import org.opensearch.indices.replication.common.ReplicationType;

import java.io.IOException;
import java.time.Instant;
import java.time.ZoneOffset;
import java.time.ZonedDateTime;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collections;
import java.util.EnumSet;
import java.util.HashMap;
import java.util.HashSet;
import java.util.Iterator;
import java.util.List;
import java.util.Locale;
import java.util.Map;
import java.util.Objects;
import java.util.Set;
import java.util.TreeSet;
import java.util.function.Function;

import static org.opensearch.cluster.metadata.Metadata.CONTEXT_MODE_PARAM;
import static org.opensearch.cluster.node.DiscoveryNodeFilters.IP_VALIDATOR;
import static org.opensearch.cluster.node.DiscoveryNodeFilters.OpType.AND;
import static org.opensearch.cluster.node.DiscoveryNodeFilters.OpType.OR;
import static org.opensearch.common.settings.Settings.readSettingsFromStream;
import static org.opensearch.common.settings.Settings.writeSettingsToStream;

/**
 * Index metadata information
 *
 * @opensearch.api
 */
@PublicApi(since = "1.0.0")
public class IndexMetadata implements Diffable<IndexMetadata>, ToXContentFragment, VerifiableWriteable {

    public static final ClusterBlock INDEX_READ_ONLY_BLOCK = new ClusterBlock(
        5,
        "index read-only (api)",
        false,
        false,
        false,
        RestStatus.FORBIDDEN,
        EnumSet.of(ClusterBlockLevel.WRITE, ClusterBlockLevel.METADATA_WRITE)
    );
    public static final ClusterBlock INDEX_READ_BLOCK = new ClusterBlock(
        7,
        "index read (api)",
        false,
        false,
        false,
        RestStatus.FORBIDDEN,
        EnumSet.of(ClusterBlockLevel.READ)
    );
    public static final ClusterBlock INDEX_WRITE_BLOCK = new ClusterBlock(
        8,
        "index write (api)",
        false,
        false,
        false,
        RestStatus.FORBIDDEN,
        EnumSet.of(ClusterBlockLevel.WRITE)
    );
    public static final ClusterBlock INDEX_METADATA_BLOCK = new ClusterBlock(
        9,
        "index metadata (api)",
        false,
        false,
        false,
        RestStatus.FORBIDDEN,
        EnumSet.of(ClusterBlockLevel.METADATA_WRITE, ClusterBlockLevel.METADATA_READ)
    );
    public static final ClusterBlock INDEX_READ_ONLY_ALLOW_DELETE_BLOCK = new ClusterBlock(
        12,
        "disk usage exceeded flood-stage watermark, index has read-only-allow-delete block",
        false,
        false,
        true,
        RestStatus.TOO_MANY_REQUESTS,
        EnumSet.of(ClusterBlockLevel.METADATA_WRITE, ClusterBlockLevel.WRITE)
    );

    public static final ClusterBlock REMOTE_READ_ONLY_ALLOW_DELETE = new ClusterBlock(
        13,
        "remote index is read-only",
        false,
        false,
        true,
        RestStatus.FORBIDDEN,
        EnumSet.of(ClusterBlockLevel.METADATA_WRITE, ClusterBlockLevel.WRITE)
    );

    /**
     * The state of the index.
     *
     * @opensearch.api
     */
    @PublicApi(since = "1.0.0")
    public enum State {
        OPEN((byte) 0),
        CLOSE((byte) 1);

        private final byte id;

        State(byte id) {
            this.id = id;
        }

        public byte id() {
            return this.id;
        }

        public static State fromId(byte id) {
            if (id == 0) {
                return OPEN;
            } else if (id == 1) {
                return CLOSE;
            }
            throw new IllegalStateException("No state match for id [" + id + "]");
        }

        public static State fromString(String state) {
            if ("open".equals(state)) {
                return OPEN;
            } else if ("close".equals(state)) {
                return CLOSE;
            }
            throw new IllegalStateException("No state match for [" + state + "]");
        }
    }

    static Setting<Integer> buildNumberOfShardsSetting() {
        /* This is a safety limit that should only be exceeded in very rare and special cases. The assumption is that
         * 99% of the users have less than 1024 shards per index. We also make it a hard check that requires restart of nodes
         * if a cluster should allow to create more than 1024 shards per index. NOTE: this does not limit the number of shards
         * per cluster. this also prevents creating stuff like a new index with millions of shards by accident which essentially
         * kills the entire cluster with OOM on the spot.*/
        final int maxNumShards = Integer.parseInt(System.getProperty(MAX_NUMBER_OF_SHARDS, "1024"));
        if (maxNumShards < 1) {
            throw new IllegalArgumentException(MAX_NUMBER_OF_SHARDS + " must be > 0");
        }
        /* This property should be provided if the default number of shards for any new index has to be changed to a value
         * other than 1. This value is applicable only if the index.number_of_shards setting is not provided as part of the
         * index creation request. */
        final int defaultNumShards = Integer.parseInt(System.getProperty(DEFAULT_NUMBER_OF_SHARDS, "1"));
        if (defaultNumShards < 1 || defaultNumShards > maxNumShards) {
            throw new IllegalArgumentException(
                DEFAULT_NUMBER_OF_SHARDS
                    + " value ["
                    + defaultNumShards
                    + "] must between "
                    + "1 and "
                    + MAX_NUMBER_OF_SHARDS
                    + " ["
                    + maxNumShards
                    + "]"
            );
        }
        return Setting.intSetting(SETTING_NUMBER_OF_SHARDS, defaultNumShards, 1, maxNumShards, Property.IndexScope, Property.Final);
    }

    public static final String INDEX_SETTING_PREFIX = "index.";
    public static final String SETTING_NUMBER_OF_SHARDS = "index.number_of_shards";
    static final String DEFAULT_NUMBER_OF_SHARDS = "opensearch.index.default_number_of_shards";
    static final String MAX_NUMBER_OF_SHARDS = "opensearch.index.max_number_of_shards";
    public static final Setting<Integer> INDEX_NUMBER_OF_SHARDS_SETTING = buildNumberOfShardsSetting();
    public static final String SETTING_NUMBER_OF_REPLICAS = "index.number_of_replicas";
    public static final Setting<Integer> INDEX_NUMBER_OF_REPLICAS_SETTING = Setting.intSetting(
        SETTING_NUMBER_OF_REPLICAS,
        1,
        0,
        Property.Dynamic,
        Property.IndexScope
    );

    /**
     * Setting to control the number of search only replicas for an index.
     * A search only replica exists solely to perform read operations for a shard and are designed to achieve
     * isolation from writers (primary shards).  This means they are not primary eligible and do not have any direct communication
     * with their primary.  Search replicas require the use of Segment Replication on the index and poll their {@link SegmentReplicationSource} for
     * updates.  //TODO: Once physical isolation is introduced, reference the setting here.
     */
    public static final String SETTING_NUMBER_OF_SEARCH_REPLICAS = "index.number_of_search_only_replicas";
    public static final Setting<Integer> INDEX_NUMBER_OF_SEARCH_REPLICAS_SETTING = Setting.intSetting(
        SETTING_NUMBER_OF_SEARCH_REPLICAS,
        0,
        0,
        Property.Dynamic,
        Property.IndexScope
    );

    public static final String SETTING_ROUTING_PARTITION_SIZE = "index.routing_partition_size";
    public static final Setting<Integer> INDEX_ROUTING_PARTITION_SIZE_SETTING = Setting.intSetting(
        SETTING_ROUTING_PARTITION_SIZE,
        1,
        1,
        Property.IndexScope
    );

    public static final Setting<Integer> INDEX_NUMBER_OF_ROUTING_SHARDS_SETTING = Setting.intSetting(
        "index.number_of_routing_shards",
        INDEX_NUMBER_OF_SHARDS_SETTING,
        1,
        new Setting.Validator<Integer>() {

            @Override
            public void validate(final Integer value) {

            }

            @Override
            public void validate(final Integer numRoutingShards, final Map<Setting<?>, Object> settings) {
                int numShards = (int) settings.get(INDEX_NUMBER_OF_SHARDS_SETTING);
                if (numRoutingShards < numShards) {
                    throw new IllegalArgumentException(
                        "index.number_of_routing_shards [" + numRoutingShards + "] must be >= index.number_of_shards [" + numShards + "]"
                    );
                }
                getRoutingFactor(numShards, numRoutingShards);
            }

            @Override
            public Iterator<Setting<?>> settings() {
                final List<Setting<?>> settings = Collections.singletonList(INDEX_NUMBER_OF_SHARDS_SETTING);
                return settings.iterator();
            }

        },
        Property.IndexScope
    );

    /**
     * Used to specify the replication type for the index. By default, document replication is used.
     */
    public static final String SETTING_REPLICATION_TYPE = "index.replication.type";
    public static final Setting<ReplicationType> INDEX_REPLICATION_TYPE_SETTING = new Setting<>(
        SETTING_REPLICATION_TYPE,
        ReplicationType.DOCUMENT.toString(),
        ReplicationType::parseString,
        new Setting.Validator<>() {

            @Override
            public void validate(final ReplicationType value) {}

            @Override
            public void validate(final ReplicationType value, final Map<Setting<?>, Object> settings) {
                final Object remoteStoreEnabled = settings.get(INDEX_REMOTE_STORE_ENABLED_SETTING);
                if (ReplicationType.SEGMENT.equals(value) == false && Objects.equals(remoteStoreEnabled, true)) {
                    throw new IllegalArgumentException(
                        "To enable "
                            + INDEX_REMOTE_STORE_ENABLED_SETTING.getKey()
                            + ", "
                            + INDEX_REPLICATION_TYPE_SETTING.getKey()
                            + " should be set to "
                            + ReplicationType.SEGMENT
                    );
                }
            }

            @Override
            public Iterator<Setting<?>> settings() {
                final List<Setting<?>> settings = List.of(INDEX_REMOTE_STORE_ENABLED_SETTING);
                return settings.iterator();
            }
        },
        Property.IndexScope,
        Property.Final
    );

    public static final String SETTING_REMOTE_STORE_ENABLED = "index.remote_store.enabled";

    public static final String SETTING_REMOTE_SEGMENT_STORE_REPOSITORY = "index.remote_store.segment.repository";

    public static final String SETTING_REMOTE_TRANSLOG_STORE_REPOSITORY = "index.remote_store.translog.repository";

    /**
     * Used to specify if the index data should be persisted in the remote store.
     */
    public static final Setting<Boolean> INDEX_REMOTE_STORE_ENABLED_SETTING = Setting.boolSetting(
        SETTING_REMOTE_STORE_ENABLED,
        false,
        new Setting.Validator<>() {

            @Override
            public void validate(final Boolean value) {}

            @Override
            public void validate(final Boolean value, final Map<Setting<?>, Object> settings) {
                final Object replicationType = settings.get(INDEX_REPLICATION_TYPE_SETTING);
                if (ReplicationType.SEGMENT.equals(replicationType) == false && value) {
                    throw new IllegalArgumentException(
                        "To enable "
                            + INDEX_REMOTE_STORE_ENABLED_SETTING.getKey()
                            + ", "
                            + INDEX_REPLICATION_TYPE_SETTING.getKey()
                            + " should be set to "
                            + ReplicationType.SEGMENT
                    );
                }
            }

            @Override
            public Iterator<Setting<?>> settings() {
                final List<Setting<?>> settings = List.of(INDEX_REPLICATION_TYPE_SETTING);
                return settings.iterator();
            }
        },
        Property.IndexScope,
        Property.PrivateIndex,
        Property.Dynamic
    );

    /**
     * Used to specify remote store repository to use for this index.
     */
    public static final Setting<String> INDEX_REMOTE_SEGMENT_STORE_REPOSITORY_SETTING = Setting.simpleString(
        SETTING_REMOTE_SEGMENT_STORE_REPOSITORY,
        new Setting.Validator<>() {

            @Override
            public void validate(final String value) {}

            @Override
            public void validate(final String value, final Map<Setting<?>, Object> settings) {
                if (value == null || value.isEmpty()) {
                    throw new IllegalArgumentException(
                        "Setting "
                            + INDEX_REMOTE_SEGMENT_STORE_REPOSITORY_SETTING.getKey()
                            + " should be provided with non-empty repository ID"
                    );
                } else {
                    validateRemoteStoreSettingEnabled(settings, INDEX_REMOTE_SEGMENT_STORE_REPOSITORY_SETTING);
                }
            }

            @Override
            public Iterator<Setting<?>> settings() {
                final List<Setting<?>> settings = Collections.singletonList(INDEX_REMOTE_STORE_ENABLED_SETTING);
                return settings.iterator();
            }
        },
        Property.IndexScope,
        Property.PrivateIndex,
        Property.Dynamic
    );

    private static void validateRemoteStoreSettingEnabled(final Map<Setting<?>, Object> settings, Setting<?> setting) {
        final Boolean isRemoteSegmentStoreEnabled = (Boolean) settings.get(INDEX_REMOTE_STORE_ENABLED_SETTING);
        if (isRemoteSegmentStoreEnabled == false) {
            throw new IllegalArgumentException(
                "Settings "
                    + setting.getKey()
                    + " can only be set/enabled when "
                    + INDEX_REMOTE_STORE_ENABLED_SETTING.getKey()
                    + " is set to true"
            );
        }
    }

    public static final Setting<String> INDEX_REMOTE_TRANSLOG_REPOSITORY_SETTING = Setting.simpleString(
        SETTING_REMOTE_TRANSLOG_STORE_REPOSITORY,
        new Setting.Validator<>() {

            @Override
            public void validate(final String value) {}

            @Override
            public void validate(final String value, final Map<Setting<?>, Object> settings) {
                if (value == null || value.isEmpty()) {
                    throw new IllegalArgumentException(
                        "Setting " + INDEX_REMOTE_TRANSLOG_REPOSITORY_SETTING.getKey() + " should be provided with non-empty repository ID"
                    );
                } else {
                    final Boolean isRemoteTranslogStoreEnabled = (Boolean) settings.get(INDEX_REMOTE_STORE_ENABLED_SETTING);
                    if (isRemoteTranslogStoreEnabled == null || isRemoteTranslogStoreEnabled == false) {
                        throw new IllegalArgumentException(
                            "Settings "
                                + INDEX_REMOTE_TRANSLOG_REPOSITORY_SETTING.getKey()
                                + " can only be set/enabled when "
                                + INDEX_REMOTE_STORE_ENABLED_SETTING.getKey()
                                + " is set to true"
                        );
                    }
                }
            }

            @Override
            public Iterator<Setting<?>> settings() {
                final List<Setting<?>> settings = Collections.singletonList(INDEX_REMOTE_STORE_ENABLED_SETTING);
                return settings.iterator();
            }
        },
        Property.IndexScope,
        Property.PrivateIndex,
        Property.Dynamic
    );

    public static final String SETTING_AUTO_EXPAND_REPLICAS = "index.auto_expand_replicas";
    public static final Setting<AutoExpandReplicas> INDEX_AUTO_EXPAND_REPLICAS_SETTING = AutoExpandReplicas.SETTING;

    /**
     * Blocks the API.
     *
     * @opensearch.api
     */
    @PublicApi(since = "1.0.0")
    public enum APIBlock implements Writeable {
        READ_ONLY("read_only", INDEX_READ_ONLY_BLOCK),
        READ("read", INDEX_READ_BLOCK),
        WRITE("write", INDEX_WRITE_BLOCK),
        METADATA("metadata", INDEX_METADATA_BLOCK),
        READ_ONLY_ALLOW_DELETE("read_only_allow_delete", INDEX_READ_ONLY_ALLOW_DELETE_BLOCK);

        final String name;
        final String settingName;
        final Setting<Boolean> setting;
        final ClusterBlock block;

        APIBlock(String name, ClusterBlock block) {
            this.name = name;
            this.settingName = "index.blocks." + name;
            this.setting = Setting.boolSetting(settingName, false, Property.Dynamic, Property.IndexScope);
            this.block = block;
        }

        public String settingName() {
            return settingName;
        }

        public Setting<Boolean> setting() {
            return setting;
        }

        public ClusterBlock getBlock() {
            return block;
        }

        public static APIBlock fromName(String name) {
            for (APIBlock block : APIBlock.values()) {
                if (block.name.equals(name)) {
                    return block;
                }
            }
            throw new IllegalArgumentException("No block found with name " + name);
        }

        public static APIBlock fromSetting(String settingName) {
            for (APIBlock block : APIBlock.values()) {
                if (block.settingName.equals(settingName)) {
                    return block;
                }
            }
            throw new IllegalArgumentException("No block found with setting name " + settingName);
        }

        @Override
        public void writeTo(StreamOutput out) throws IOException {
            out.writeVInt(ordinal());
        }

        public static APIBlock readFrom(StreamInput input) throws IOException {
            return APIBlock.values()[input.readVInt()];
        }
    }

    public static final String SETTING_READ_ONLY = APIBlock.READ_ONLY.settingName();
    public static final Setting<Boolean> INDEX_READ_ONLY_SETTING = APIBlock.READ_ONLY.setting();

    public static final String SETTING_BLOCKS_READ = APIBlock.READ.settingName();
    public static final Setting<Boolean> INDEX_BLOCKS_READ_SETTING = APIBlock.READ.setting();

    public static final String SETTING_BLOCKS_WRITE = APIBlock.WRITE.settingName();
    public static final Setting<Boolean> INDEX_BLOCKS_WRITE_SETTING = APIBlock.WRITE.setting();

    public static final String SETTING_BLOCKS_METADATA = APIBlock.METADATA.settingName();
    public static final Setting<Boolean> INDEX_BLOCKS_METADATA_SETTING = APIBlock.METADATA.setting();

    public static final String SETTING_READ_ONLY_ALLOW_DELETE = APIBlock.READ_ONLY_ALLOW_DELETE.settingName();
    public static final Setting<Boolean> INDEX_BLOCKS_READ_ONLY_ALLOW_DELETE_SETTING = APIBlock.READ_ONLY_ALLOW_DELETE.setting();

    public static final String SETTING_VERSION_CREATED = "index.version.created";

    public static final Setting<Version> SETTING_INDEX_VERSION_CREATED = Setting.versionSetting(
        SETTING_VERSION_CREATED,
        Version.V_EMPTY,
        Property.IndexScope,
        Property.PrivateIndex
    );

    public static final String SETTING_VERSION_CREATED_STRING = "index.version.created_string";
    public static final String SETTING_VERSION_UPGRADED = "index.version.upgraded";
    public static final String SETTING_VERSION_UPGRADED_STRING = "index.version.upgraded_string";
    public static final String SETTING_CREATION_DATE = "index.creation_date";
    /**
     * The user provided name for an index. This is the plain string provided by the user when the index was created.
     * It might still contain date math expressions etc. (added in 5.0)
     */
    public static final String SETTING_INDEX_PROVIDED_NAME = "index.provided_name";
    public static final String SETTING_PRIORITY = "index.priority";
    public static final Setting<Integer> INDEX_PRIORITY_SETTING = Setting.intSetting(
        "index.priority",
        1,
        0,
        Property.Dynamic,
        Property.IndexScope
    );
    public static final String SETTING_CREATION_DATE_STRING = "index.creation_date_string";
    public static final String SETTING_INDEX_UUID = "index.uuid";
    public static final String SETTING_HISTORY_UUID = "index.history.uuid";
    public static final String SETTING_DATA_PATH = "index.data_path";
    public static final Setting<String> INDEX_DATA_PATH_SETTING = new Setting<>(
        SETTING_DATA_PATH,
        "",
        Function.identity(),
        Property.IndexScope
    );
    public static final String INDEX_UUID_NA_VALUE = Strings.UNKNOWN_UUID_VALUE;

    public static final String INDEX_ROUTING_REQUIRE_GROUP_PREFIX = "index.routing.allocation.require";
    public static final String INDEX_ROUTING_INCLUDE_GROUP_PREFIX = "index.routing.allocation.include";
    public static final String INDEX_ROUTING_EXCLUDE_GROUP_PREFIX = "index.routing.allocation.exclude";
    public static final Setting.AffixSetting<String> INDEX_ROUTING_REQUIRE_GROUP_SETTING = Setting.prefixKeySetting(
        INDEX_ROUTING_REQUIRE_GROUP_PREFIX + ".",
        key -> Setting.simpleString(key, value -> IP_VALIDATOR.accept(key, value), Property.Dynamic, Property.IndexScope)
    );
    public static final Setting.AffixSetting<String> INDEX_ROUTING_INCLUDE_GROUP_SETTING = Setting.prefixKeySetting(
        INDEX_ROUTING_INCLUDE_GROUP_PREFIX + ".",
        key -> Setting.simpleString(key, value -> IP_VALIDATOR.accept(key, value), Property.Dynamic, Property.IndexScope)
    );
    public static final Setting.AffixSetting<String> INDEX_ROUTING_EXCLUDE_GROUP_SETTING = Setting.prefixKeySetting(
        INDEX_ROUTING_EXCLUDE_GROUP_PREFIX + ".",
        key -> Setting.simpleString(key, value -> IP_VALIDATOR.accept(key, value), Property.Dynamic, Property.IndexScope)
    );
    public static final Setting.AffixSetting<String> INDEX_ROUTING_INITIAL_RECOVERY_GROUP_SETTING = Setting.prefixKeySetting(
        "index.routing.allocation.initial_recovery.",
        key -> Setting.simpleString(key)
    );

    /**
     * The number of active shard copies to check for before proceeding with a write operation.
     */
    public static final Setting<ActiveShardCount> SETTING_WAIT_FOR_ACTIVE_SHARDS = new Setting<>(
        "index.write.wait_for_active_shards",
        "1",
        ActiveShardCount::parseString,
        Setting.Property.Dynamic,
        Setting.Property.IndexScope
    );

    public static final String SETTING_INDEX_HIDDEN = "index.hidden";
    /**
     * Whether the index is considered hidden or not. A hidden index will not be resolved in
     * normal wildcard searches unless explicitly allowed
     */
    public static final Setting<Boolean> INDEX_HIDDEN_SETTING = Setting.boolSetting(
        SETTING_INDEX_HIDDEN,
        false,
        Property.Dynamic,
        Property.IndexScope
    );

    /**
     * an internal index format description, allowing us to find out if this index is upgraded or needs upgrading
     */
    private static final String INDEX_FORMAT = "index.format";
    public static final Setting<Integer> INDEX_FORMAT_SETTING = Setting.intSetting(
        INDEX_FORMAT,
        0,
        Setting.Property.IndexScope,
        Setting.Property.Final
    );

    public static final String KEY_IN_SYNC_ALLOCATIONS = "in_sync_allocations";
    static final String KEY_VERSION = "version";
    static final String KEY_MAPPING_VERSION = "mapping_version";
    static final String KEY_SETTINGS_VERSION = "settings_version";
    static final String KEY_ALIASES_VERSION = "aliases_version";
    static final String KEY_ROUTING_NUM_SHARDS = "routing_num_shards";
    static final String KEY_SETTINGS = "settings";
    static final String KEY_STATE = "state";
    static final String KEY_MAPPINGS = "mappings";
    static final String KEY_ALIASES = "aliases";
    static final String KEY_ROLLOVER_INFOS = "rollover_info";
    static final String KEY_SYSTEM = "system";
    public static final String KEY_PRIMARY_TERMS = "primary_terms";
    public static final String REMOTE_STORE_CUSTOM_KEY = "remote_store";
    public static final String TRANSLOG_METADATA_KEY = "translog_metadata";
    public static final String CONTEXT_KEY = "context";

    public static final String INDEX_STATE_FILE_PREFIX = "state-";

    static final Version SYSTEM_INDEX_FLAG_ADDED = LegacyESVersion.V_7_10_0;

    private final int routingNumShards;
    private final int routingFactor;
    private final int routingPartitionSize;

    private final int numberOfShards;
    private final int numberOfReplicas;
    private final int numberOfSearchOnlyReplicas;

    private final Index index;
    private final long version;

    private final long mappingVersion;

    private final long settingsVersion;

    private final long aliasesVersion;

    private final long[] primaryTerms;

    private final State state;

    private final Map<String, AliasMetadata> aliases;

    private final Settings settings;

    private final Map<String, MappingMetadata> mappings;

    private final Map<String, DiffableStringMap> customData;

    private final Map<Integer, Set<String>> inSyncAllocationIds;

    private final transient int totalNumberOfShards;

    private final DiscoveryNodeFilters requireFilters;
    private final DiscoveryNodeFilters includeFilters;
    private final DiscoveryNodeFilters excludeFilters;
    private final DiscoveryNodeFilters initialRecoveryFilters;

    private final Version indexCreatedVersion;
    private final Version indexUpgradedVersion;

    private final ActiveShardCount waitForActiveShards;
    private final Map<String, RolloverInfo> rolloverInfos;
    private final boolean isSystem;
    private final boolean isRemoteSnapshot;

    private final int indexTotalShardsPerNodeLimit;

    private final Context context;

    private IndexMetadata(
        final Index index,
        final long version,
        final long mappingVersion,
        final long settingsVersion,
        final long aliasesVersion,
        final long[] primaryTerms,
        final State state,
        final int numberOfShards,
        final int numberOfReplicas,
        final int numberOfSearchOnlyReplicas,
        final Settings settings,
        final Map<String, MappingMetadata> mappings,
        final Map<String, AliasMetadata> aliases,
        final Map<String, DiffableStringMap> customData,
        final Map<Integer, Set<String>> inSyncAllocationIds,
        final DiscoveryNodeFilters requireFilters,
        final DiscoveryNodeFilters initialRecoveryFilters,
        final DiscoveryNodeFilters includeFilters,
        final DiscoveryNodeFilters excludeFilters,
        final Version indexCreatedVersion,
        final Version indexUpgradedVersion,
        final int routingNumShards,
        final int routingPartitionSize,
        final ActiveShardCount waitForActiveShards,
        final Map<String, RolloverInfo> rolloverInfos,
        final boolean isSystem,
        final int indexTotalShardsPerNodeLimit,
        final Context context
    ) {

        this.index = index;
        this.version = version;
        assert mappingVersion >= 0 : mappingVersion;
        this.mappingVersion = mappingVersion;
        assert settingsVersion >= 0 : settingsVersion;
        this.settingsVersion = settingsVersion;
        assert aliasesVersion >= 0 : aliasesVersion;
        this.aliasesVersion = aliasesVersion;
        this.primaryTerms = primaryTerms;
        assert primaryTerms.length == numberOfShards;
        this.state = state;
        this.numberOfShards = numberOfShards;
        this.numberOfReplicas = numberOfReplicas;
        this.numberOfSearchOnlyReplicas = numberOfSearchOnlyReplicas;
        this.totalNumberOfShards = numberOfShards * (numberOfReplicas + numberOfSearchOnlyReplicas + 1);
        this.settings = settings;
        this.mappings = Collections.unmodifiableMap(mappings);
        this.customData = Collections.unmodifiableMap(customData);
        this.aliases = Collections.unmodifiableMap(aliases);
        this.inSyncAllocationIds = Collections.unmodifiableMap(inSyncAllocationIds);
        this.requireFilters = requireFilters;
        this.includeFilters = includeFilters;
        this.excludeFilters = excludeFilters;
        this.initialRecoveryFilters = initialRecoveryFilters;
        this.indexCreatedVersion = indexCreatedVersion;
        this.indexUpgradedVersion = indexUpgradedVersion;
        this.routingNumShards = routingNumShards;
        this.routingFactor = routingNumShards / numberOfShards;
        this.routingPartitionSize = routingPartitionSize;
        this.waitForActiveShards = waitForActiveShards;
        this.rolloverInfos = Collections.unmodifiableMap(rolloverInfos);
        this.isSystem = isSystem;
        this.isRemoteSnapshot = IndexModule.Type.REMOTE_SNAPSHOT.match(this.settings);
        this.indexTotalShardsPerNodeLimit = indexTotalShardsPerNodeLimit;
        this.context = context;
        assert numberOfShards * routingFactor == routingNumShards : routingNumShards + " must be a multiple of " + numberOfShards;
    }

    public Index getIndex() {
        return index;
    }

    public String getIndexUUID() {
        return index.getUUID();
    }

    /**
     * Test whether the current index UUID is the same as the given one. Returns true if either are _na_
     */
    public boolean isSameUUID(String otherUUID) {
        assert otherUUID != null;
        assert getIndexUUID() != null;
        if (INDEX_UUID_NA_VALUE.equals(otherUUID) || INDEX_UUID_NA_VALUE.equals(getIndexUUID())) {
            return true;
        }
        return otherUUID.equals(getIndexUUID());
    }

    public long getVersion() {
        return this.version;
    }

    public long getMappingVersion() {
        return mappingVersion;
    }

    public long getSettingsVersion() {
        return settingsVersion;
    }

    public long getAliasesVersion() {
        return aliasesVersion;
    }

    /**
     * The term of the current selected primary. This is a non-negative number incremented when
     * a primary shard is assigned after a full cluster restart or a replica shard is promoted to a primary.
     * <p>
     * Note: since we increment the term every time a shard is assigned, the term for any operational shard (i.e., a shard
     * that can be indexed into) is larger than 0. See {@link IndexMetadataUpdater#applyChanges}.
     **/
    public long primaryTerm(int shardId) {
        return this.primaryTerms[shardId];
    }

    /**
     * Return the {@link Version} on which this index has been created. This
     * information is typically useful for backward compatibility.
     */
    public Version getCreationVersion() {
        return indexCreatedVersion;
    }

    /**
     * Return the {@link Version} on which this index has been upgraded. This
     * information is typically useful for backward compatibility.
     */
    public Version getUpgradedVersion() {
        return indexUpgradedVersion;
    }

    public long getCreationDate() {
        return settings.getAsLong(SETTING_CREATION_DATE, -1L);
    }

    public State getState() {
        return this.state;
    }

    public int getNumberOfShards() {
        return numberOfShards;
    }

    public int getNumberOfReplicas() {
        return numberOfReplicas;
    }

    public int getNumberOfSearchOnlyReplicas() {
        return numberOfSearchOnlyReplicas;
    }

    public int getRoutingPartitionSize() {
        return routingPartitionSize;
    }

    public boolean isRoutingPartitionedIndex() {
        return routingPartitionSize != 1;
    }

    public int getTotalNumberOfShards() {
        return totalNumberOfShards;
    }

    /**
     * Returns the configured {@link #SETTING_WAIT_FOR_ACTIVE_SHARDS}, which defaults
     * to an active shard count of 1 if not specified.
     */
    public ActiveShardCount getWaitForActiveShards() {
        return waitForActiveShards;
    }

    public Settings getSettings() {
        return settings;
    }

    public Map<String, AliasMetadata> getAliases() {
        return this.aliases;
    }

    /**
     * Return the concrete mapping for this index or {@code null} if this index has no mappings at all.
     */
    @Nullable
    public MappingMetadata mapping() {
        for (final MappingMetadata cursor : mappings.values()) {
            return cursor;
        }
        return null;
    }

    public static final String INDEX_RESIZE_SOURCE_UUID_KEY = "index.resize.source.uuid";
    public static final String INDEX_RESIZE_SOURCE_NAME_KEY = "index.resize.source.name";
    public static final Setting<String> INDEX_RESIZE_SOURCE_UUID = Setting.simpleString(INDEX_RESIZE_SOURCE_UUID_KEY);
    public static final Setting<String> INDEX_RESIZE_SOURCE_NAME = Setting.simpleString(INDEX_RESIZE_SOURCE_NAME_KEY);

    public Index getResizeSourceIndex() {
        return INDEX_RESIZE_SOURCE_UUID.exists(settings)
            ? new Index(INDEX_RESIZE_SOURCE_NAME.get(settings), INDEX_RESIZE_SOURCE_UUID.get(settings))
            : null;
    }

    Map<String, DiffableStringMap> getCustomData() {
        return this.customData;
    }

    public Map<String, String> getCustomData(final String key) {
        return this.customData.get(key);
    }

    public Map<Integer, Set<String>> getInSyncAllocationIds() {
        return inSyncAllocationIds;
    }

    public Map<String, RolloverInfo> getRolloverInfos() {
        return rolloverInfos;
    }

    public Set<String> inSyncAllocationIds(int shardId) {
        assert shardId >= 0 && shardId < numberOfShards;
        return inSyncAllocationIds.get(shardId);
    }

    public int getIndexTotalShardsPerNodeLimit() {
        return this.indexTotalShardsPerNodeLimit;
    }

    @Nullable
    public DiscoveryNodeFilters requireFilters() {
        return requireFilters;
    }

    @Nullable
    public DiscoveryNodeFilters getInitialRecoveryFilters() {
        return initialRecoveryFilters;
    }

    @Nullable
    public DiscoveryNodeFilters includeFilters() {
        return includeFilters;
    }

    @Nullable
    public DiscoveryNodeFilters excludeFilters() {
        return excludeFilters;
    }

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

        IndexMetadata that = (IndexMetadata) o;

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

        if (!aliases.equals(that.aliases)) {
            return false;
        }
        if (!index.equals(that.index)) {
            return false;
        }
        if (!mappings.equals(that.mappings)) {
            return false;
        }
        if (!settings.equals(that.settings)) {
            return false;
        }
        if (state != that.state) {
            return false;
        }
        if (!customData.equals(that.customData)) {
            return false;
        }
        if (routingNumShards != that.routingNumShards) {
            return false;
        }
        if (routingFactor != that.routingFactor) {
            return false;
        }
        if (Arrays.equals(primaryTerms, that.primaryTerms) == false) {
            return false;
        }
        if (!inSyncAllocationIds.equals(that.inSyncAllocationIds)) {
            return false;
        }
        if (rolloverInfos.equals(that.rolloverInfos) == false) {
            return false;
        }
        if (isSystem != that.isSystem) {
            return false;
        }
        if (!Objects.equals(context, that.context)) {
            return false;
        }
        return true;
    }

    @Override
    public int hashCode() {
        int result = index.hashCode();
        result = 31 * result + Long.hashCode(version);
        result = 31 * result + state.hashCode();
        result = 31 * result + aliases.hashCode();
        result = 31 * result + settings.hashCode();
        result = 31 * result + mappings.hashCode();
        result = 31 * result + customData.hashCode();
        result = 31 * result + Long.hashCode(routingFactor);
        result = 31 * result + Long.hashCode(routingNumShards);
        result = 31 * result + Arrays.hashCode(primaryTerms);
        result = 31 * result + inSyncAllocationIds.hashCode();
        result = 31 * result + rolloverInfos.hashCode();
        result = 31 * result + Boolean.hashCode(isSystem);
        result = 31 * result + Objects.hashCode(context);
        return result;
    }

    @Override
    public Diff<IndexMetadata> diff(IndexMetadata previousState) {
        return new IndexMetadataDiff(previousState, this);
    }

    public static Diff<IndexMetadata> readDiffFrom(StreamInput in) throws IOException {
        return new IndexMetadataDiff(in);
    }

    public static IndexMetadata fromXContent(XContentParser parser) throws IOException {
        return Builder.fromXContent(parser);
    }

    @Override
    public XContentBuilder toXContent(XContentBuilder builder, Params params) throws IOException {
        Builder.toXContent(this, builder, params);
        return builder;
    }

    /**
     * A diff of index metadata.
     *
     * @opensearch.internal
     */
    private static class IndexMetadataDiff implements Diff<IndexMetadata> {

        private final String index;
        private final int routingNumShards;
        private final long version;
        private final long mappingVersion;
        private final long settingsVersion;
        private final long aliasesVersion;
        private final long[] primaryTerms;
        private final State state;
        private final Settings settings;
        private final Diff<Map<String, MappingMetadata>> mappings;
        private final Diff<Map<String, AliasMetadata>> aliases;
        private final Diff<Map<String, DiffableStringMap>> customData;
        private final Diff<Map<Integer, Set<String>>> inSyncAllocationIds;
        private final Diff<Map<String, RolloverInfo>> rolloverInfos;
        private final boolean isSystem;
        private final Context context;

        IndexMetadataDiff(IndexMetadata before, IndexMetadata after) {
            index = after.index.getName();
            version = after.version;
            mappingVersion = after.mappingVersion;
            settingsVersion = after.settingsVersion;
            aliasesVersion = after.aliasesVersion;
            routingNumShards = after.routingNumShards;
            state = after.state;
            settings = after.settings;
            primaryTerms = after.primaryTerms;
            mappings = DiffableUtils.diff(before.mappings, after.mappings, DiffableUtils.getStringKeySerializer());
            aliases = DiffableUtils.diff(before.aliases, after.aliases, DiffableUtils.getStringKeySerializer());
            customData = DiffableUtils.diff(before.customData, after.customData, DiffableUtils.getStringKeySerializer());
            inSyncAllocationIds = DiffableUtils.diff(
                before.inSyncAllocationIds,
                after.inSyncAllocationIds,
                DiffableUtils.getVIntKeySerializer(),
                DiffableUtils.StringSetValueSerializer.getInstance()
            );
            rolloverInfos = DiffableUtils.diff(before.rolloverInfos, after.rolloverInfos, DiffableUtils.getStringKeySerializer());
            isSystem = after.isSystem;
            context = after.context;
        }

        private static final DiffableUtils.DiffableValueReader<String, AliasMetadata> ALIAS_METADATA_DIFF_VALUE_READER =
            new DiffableUtils.DiffableValueReader<>(AliasMetadata::new, AliasMetadata::readDiffFrom);
        private static final DiffableUtils.DiffableValueReader<String, MappingMetadata> MAPPING_DIFF_VALUE_READER =
            new DiffableUtils.DiffableValueReader<>(MappingMetadata::new, MappingMetadata::readDiffFrom);
        private static final DiffableUtils.DiffableValueReader<String, DiffableStringMap> CUSTOM_DIFF_VALUE_READER =
            new DiffableUtils.DiffableValueReader<>(DiffableStringMap::readFrom, DiffableStringMap::readDiffFrom);
        private static final DiffableUtils.DiffableValueReader<String, RolloverInfo> ROLLOVER_INFO_DIFF_VALUE_READER =
            new DiffableUtils.DiffableValueReader<>(RolloverInfo::new, RolloverInfo::readDiffFrom);

        IndexMetadataDiff(StreamInput in) throws IOException {
            index = in.readString();
            routingNumShards = in.readInt();
            version = in.readLong();
            mappingVersion = in.readVLong();
            settingsVersion = in.readVLong();
            if (in.getVersion().onOrAfter(LegacyESVersion.V_7_2_0)) {
                aliasesVersion = in.readVLong();
            } else {
                aliasesVersion = 1;
            }
            state = State.fromId(in.readByte());
            settings = Settings.readSettingsFromStream(in);
            primaryTerms = in.readVLongArray();
            mappings = DiffableUtils.readJdkMapDiff(in, DiffableUtils.getStringKeySerializer(), MAPPING_DIFF_VALUE_READER);
            aliases = DiffableUtils.readJdkMapDiff(in, DiffableUtils.getStringKeySerializer(), ALIAS_METADATA_DIFF_VALUE_READER);
            customData = DiffableUtils.readJdkMapDiff(in, DiffableUtils.getStringKeySerializer(), CUSTOM_DIFF_VALUE_READER);
            inSyncAllocationIds = DiffableUtils.readJdkMapDiff(
                in,
                DiffableUtils.getVIntKeySerializer(),
                DiffableUtils.StringSetValueSerializer.getInstance()
            );
            rolloverInfos = DiffableUtils.readJdkMapDiff(in, DiffableUtils.getStringKeySerializer(), ROLLOVER_INFO_DIFF_VALUE_READER);
            if (in.getVersion().onOrAfter(SYSTEM_INDEX_FLAG_ADDED)) {
                isSystem = in.readBoolean();
            } else {
                isSystem = false;
            }
            if (in.getVersion().onOrAfter(Version.V_2_17_0)) {
                context = in.readOptionalWriteable(Context::new);
            } else {
                context = null;
            }
        }

        @Override
        public void writeTo(StreamOutput out) throws IOException {
            out.writeString(index);
            out.writeInt(routingNumShards);
            out.writeLong(version);
            out.writeVLong(mappingVersion);
            out.writeVLong(settingsVersion);
            if (out.getVersion().onOrAfter(LegacyESVersion.V_7_2_0)) {
                out.writeVLong(aliasesVersion);
            }
            out.writeByte(state.id);
            Settings.writeSettingsToStream(settings, out);
            out.writeVLongArray(primaryTerms);
            mappings.writeTo(out);
            aliases.writeTo(out);
            customData.writeTo(out);
            inSyncAllocationIds.writeTo(out);
            rolloverInfos.writeTo(out);

            if (out.getVersion().onOrAfter(SYSTEM_INDEX_FLAG_ADDED)) {
                out.writeBoolean(isSystem);
            }
            if (out.getVersion().onOrAfter(Version.V_2_17_0)) {
                out.writeOptionalWriteable(context);
            }
        }

        @Override
        public IndexMetadata apply(IndexMetadata part) {
            Builder builder = builder(index);
            builder.version(version);
            builder.mappingVersion(mappingVersion);
            builder.settingsVersion(settingsVersion);
            builder.aliasesVersion(aliasesVersion);
            builder.setRoutingNumShards(routingNumShards);
            builder.state(state);
            builder.settings(settings);
            builder.primaryTerms(primaryTerms);
            builder.mappings.putAll(mappings.apply(part.mappings));
            builder.aliases.putAll(aliases.apply(part.aliases));
            builder.customMetadata.putAll(customData.apply(part.customData));
            builder.inSyncAllocationIds.putAll(inSyncAllocationIds.apply(part.inSyncAllocationIds));
            builder.rolloverInfos.putAll(rolloverInfos.apply(part.rolloverInfos));
            builder.system(part.isSystem);
            builder.context(context);
            return builder.build();
        }
    }

    public static IndexMetadata readFrom(StreamInput in) throws IOException {
        Builder builder = new Builder(in.readString());
        builder.version(in.readLong());
        builder.mappingVersion(in.readVLong());
        builder.settingsVersion(in.readVLong());
        if (in.getVersion().onOrAfter(LegacyESVersion.V_7_2_0)) {
            builder.aliasesVersion(in.readVLong());
        } else {
            builder.aliasesVersion(1);
        }
        builder.setRoutingNumShards(in.readInt());
        builder.state(State.fromId(in.readByte()));
        builder.settings(readSettingsFromStream(in));
        builder.primaryTerms(in.readVLongArray());
        int mappingsSize = in.readVInt();
        for (int i = 0; i < mappingsSize; i++) {
            MappingMetadata mappingMd = new MappingMetadata(in);
            builder.putMapping(mappingMd);
        }
        int aliasesSize = in.readVInt();
        for (int i = 0; i < aliasesSize; i++) {
            AliasMetadata aliasMd = new AliasMetadata(in);
            builder.putAlias(aliasMd);
        }
        int customSize = in.readVInt();
        for (int i = 0; i < customSize; i++) {
            String key = in.readString();
            DiffableStringMap custom = DiffableStringMap.readFrom(in);
            builder.putCustom(key, custom);
        }
        int inSyncAllocationIdsSize = in.readVInt();
        for (int i = 0; i < inSyncAllocationIdsSize; i++) {
            int key = in.readVInt();
            Set<String> allocationIds = DiffableUtils.StringSetValueSerializer.getInstance().read(in, key);
            builder.putInSyncAllocationIds(key, allocationIds);
        }
        int rolloverAliasesSize = in.readVInt();
        for (int i = 0; i < rolloverAliasesSize; i++) {
            builder.putRolloverInfo(new RolloverInfo(in));
        }
        if (in.getVersion().onOrAfter(SYSTEM_INDEX_FLAG_ADDED)) {
            builder.system(in.readBoolean());
        }
        if (in.getVersion().onOrAfter(Version.V_2_17_0)) {
            builder.context(in.readOptionalWriteable(Context::new));
        }
        return builder.build();
    }

    @Override
    public void writeTo(StreamOutput out) throws IOException {
        out.writeString(index.getName()); // uuid will come as part of settings
        out.writeLong(version);
        out.writeVLong(mappingVersion);
        out.writeVLong(settingsVersion);
        if (out.getVersion().onOrAfter(LegacyESVersion.V_7_2_0)) {
            out.writeVLong(aliasesVersion);
        }
        out.writeInt(routingNumShards);
        out.writeByte(state.id());
        writeSettingsToStream(settings, out);
        out.writeVLongArray(primaryTerms);
        out.writeVInt(mappings.size());
        for (final MappingMetadata cursor : mappings.values()) {
            cursor.writeTo(out);
        }
        out.writeVInt(aliases.size());
        for (final AliasMetadata cursor : aliases.values()) {
            cursor.writeTo(out);
        }
        out.writeVInt(customData.size());
        for (final Map.Entry<String, DiffableStringMap> cursor : customData.entrySet()) {
            out.writeString(cursor.getKey());
            cursor.getValue().writeTo(out);
        }
        out.writeVInt(inSyncAllocationIds.size());
        for (final Map.Entry<Integer, Set<String>> cursor : inSyncAllocationIds.entrySet()) {
            out.writeVInt(cursor.getKey());
            DiffableUtils.StringSetValueSerializer.getInstance().write(cursor.getValue(), out);
        }
        out.writeVInt(rolloverInfos.size());
        for (final RolloverInfo cursor : rolloverInfos.values()) {
            cursor.writeTo(out);
        }
        if (out.getVersion().onOrAfter(SYSTEM_INDEX_FLAG_ADDED)) {
            out.writeBoolean(isSystem);
        }
        if (out.getVersion().onOrAfter(Version.V_2_17_0)) {
            out.writeOptionalWriteable(context);
        }
    }

    @Override
    public void writeVerifiableTo(StreamOutput out) throws IOException {
        out.writeString(index.getName()); // uuid will come as part of settings
        out.writeLong(version);
        out.writeVLong(mappingVersion);
        out.writeVLong(settingsVersion);
        out.writeVLong(aliasesVersion);
        out.writeInt(routingNumShards);
        out.writeByte(state.id());
        writeSettingsToStream(settings, out);
        out.writeVLongArray(primaryTerms);
        ((BufferedChecksumStreamOutput) out).writeMapValues(mappings, (stream, val) -> val.writeTo(stream));
        ((BufferedChecksumStreamOutput) out).writeMapValues(aliases, (stream, val) -> val.writeTo(stream));
        out.writeMap(customData, StreamOutput::writeString, (stream, val) -> val.writeTo(stream));
        out.writeMap(
            inSyncAllocationIds,
            StreamOutput::writeVInt,
            (stream, val) -> DiffableUtils.StringSetValueSerializer.getInstance().write(new TreeSet<>(val), stream)
        );
        ((BufferedChecksumStreamOutput) out).writeMapValues(rolloverInfos, (stream, val) -> val.writeTo(stream));
        out.writeBoolean(isSystem);
        if (out.getVersion().onOrAfter(Version.V_2_17_0)) {
            out.writeOptionalWriteable(context);
        }
    }

    public boolean isSystem() {
        return isSystem;
    }

    public Context context() {
        return context;
    }

    public boolean isRemoteSnapshot() {
        return isRemoteSnapshot;
    }

    public static Builder builder(String index) {
        return new Builder(index);
    }

    public static Builder builder(IndexMetadata indexMetadata) {
        return new Builder(indexMetadata);
    }

    /**
     * Builder of index metadata.
     *
     * @opensearch.api
     */
    @PublicApi(since = "1.0.0")
    public static class Builder {

        private String index;
        private State state = State.OPEN;
        private long version = 1;
        private long mappingVersion = 1;
        private long settingsVersion = 1;
        private long aliasesVersion = 1;
        private long[] primaryTerms = null;
        private Settings settings = Settings.Builder.EMPTY_SETTINGS;
        private final Map<String, MappingMetadata> mappings;
        private final Map<String, AliasMetadata> aliases;
        private final Map<String, DiffableStringMap> customMetadata;
        private final Map<Integer, Set<String>> inSyncAllocationIds;
        private final Map<String, RolloverInfo> rolloverInfos;
        private Integer routingNumShards;
        private boolean isSystem;
        private Context context;

        public Builder(String index) {
            this.index = index;
            this.mappings = new HashMap<>();
            this.aliases = new HashMap<>();
            this.customMetadata = new HashMap<>();
            this.inSyncAllocationIds = new HashMap<>();
            this.rolloverInfos = new HashMap<>();
            this.isSystem = false;
        }

        public Builder(IndexMetadata indexMetadata) {
            this.index = indexMetadata.getIndex().getName();
            this.state = indexMetadata.state;
            this.version = indexMetadata.version;
            this.mappingVersion = indexMetadata.mappingVersion;
            this.settingsVersion = indexMetadata.settingsVersion;
            this.aliasesVersion = indexMetadata.aliasesVersion;
            this.settings = indexMetadata.getSettings();
            this.primaryTerms = indexMetadata.primaryTerms.clone();
            this.mappings = new HashMap<>(indexMetadata.mappings);
            this.aliases = new HashMap<>(indexMetadata.aliases);
            this.customMetadata = new HashMap<>(indexMetadata.customData);
            this.routingNumShards = indexMetadata.routingNumShards;
            this.inSyncAllocationIds = new HashMap<>(indexMetadata.inSyncAllocationIds);
            this.rolloverInfos = new HashMap<>(indexMetadata.rolloverInfos);
            this.isSystem = indexMetadata.isSystem;
            this.context = indexMetadata.context;
        }

        public Builder index(String index) {
            this.index = index;
            return this;
        }

        public Builder numberOfShards(int numberOfShards) {
            settings = Settings.builder().put(settings).put(SETTING_NUMBER_OF_SHARDS, numberOfShards).build();
            return this;
        }

        /**
         * Sets the number of shards that should be used for routing. This should only be used if the number of shards in
         * an index has changed ie if the index is shrunk.
         */
        public Builder setRoutingNumShards(int routingNumShards) {
            this.routingNumShards = routingNumShards;
            return this;
        }

        /**
         * Returns number of shards that should be used for routing. By default this method will return the number of shards
         * for this index.
         *
         * @see #setRoutingNumShards(int)
         * @see #numberOfShards()
         */
        public int getRoutingNumShards() {
            return routingNumShards == null ? numberOfShards() : routingNumShards;
        }

        /**
         * Returns the number of shards.
         *
         * @return the provided value or -1 if it has not been set.
         */
        public int numberOfShards() {
            return settings.getAsInt(SETTING_NUMBER_OF_SHARDS, -1);
        }

        public Builder numberOfReplicas(int numberOfReplicas) {
            settings = Settings.builder().put(settings).put(SETTING_NUMBER_OF_REPLICAS, numberOfReplicas).build();
            return this;
        }

        public Builder numberOfSearchReplicas(int numberOfSearchReplicas) {
            settings = Settings.builder().put(settings).put(SETTING_NUMBER_OF_SEARCH_REPLICAS, numberOfSearchReplicas).build();
            return this;
        }

        public Builder routingPartitionSize(int routingPartitionSize) {
            settings = Settings.builder().put(settings).put(SETTING_ROUTING_PARTITION_SIZE, routingPartitionSize).build();
            return this;
        }

        public Builder creationDate(long creationDate) {
            settings = Settings.builder().put(settings).put(SETTING_CREATION_DATE, creationDate).build();
            return this;
        }

        public Builder settings(Settings.Builder settings) {
            return settings(settings.build());
        }

        public Builder settings(Settings settings) {
            this.settings = settings;
            return this;
        }

        public MappingMetadata mapping() {
            return mappings.get(MapperService.SINGLE_MAPPING_NAME);
        }

        public Builder putMapping(String source) throws IOException {
            putMapping(
                new MappingMetadata(
                    MapperService.SINGLE_MAPPING_NAME,
                    XContentHelper.convertToMap(MediaTypeRegistry.xContent(source).xContent(), source, true)
                )
            );
            return this;
        }

        public Builder putMapping(MappingMetadata mappingMd) {
            mappings.clear();
            if (mappingMd != null) {
                mappings.put(mappingMd.type(), mappingMd);
            }
            return this;
        }

        public Builder state(State state) {
            this.state = state;
            return this;
        }

        public Builder putAlias(AliasMetadata aliasMetadata) {
            aliases.put(aliasMetadata.alias(), aliasMetadata);
            return this;
        }

        public Builder putAlias(AliasMetadata.Builder aliasMetadata) {
            aliases.put(aliasMetadata.alias(), aliasMetadata.build());
            return this;
        }

        public Builder removeAlias(String alias) {
            aliases.remove(alias);
            return this;
        }

        public Builder removeAllAliases() {
            aliases.clear();
            return this;
        }

        public Builder putCustom(String type, Map<String, String> customIndexMetadata) {
            this.customMetadata.put(type, new DiffableStringMap(customIndexMetadata));
            return this;
        }

        public Map<String, String> removeCustom(String type) {
            return this.customMetadata.remove(type);
        }

        public Set<String> getInSyncAllocationIds(int shardId) {
            return inSyncAllocationIds.get(shardId);
        }

        public Builder putInSyncAllocationIds(int shardId, Set<String> allocationIds) {
            inSyncAllocationIds.put(shardId, new HashSet<>(allocationIds));
            return this;
        }

        public Builder putRolloverInfo(RolloverInfo rolloverInfo) {
            rolloverInfos.put(rolloverInfo.getAlias(), rolloverInfo);
            return this;
        }

        public long version() {
            return this.version;
        }

        public Builder version(long version) {
            this.version = version;
            return this;
        }

        public long mappingVersion() {
            return mappingVersion;
        }

        public Builder mappingVersion(final long mappingVersion) {
            this.mappingVersion = mappingVersion;
            return this;
        }

        public long settingsVersion() {
            return settingsVersion;
        }

        public Builder settingsVersion(final long settingsVersion) {
            this.settingsVersion = settingsVersion;
            return this;
        }

        public long aliasesVersion() {
            return aliasesVersion;
        }

        public Builder aliasesVersion(final long aliasesVersion) {
            this.aliasesVersion = aliasesVersion;
            return this;
        }

        /**
         * returns the primary term for the given shard.
         * See {@link IndexMetadata#primaryTerm(int)} for more information.
         */
        public long primaryTerm(int shardId) {
            if (primaryTerms == null) {
                initializePrimaryTerms();
            }
            return this.primaryTerms[shardId];
        }

        /**
         * sets the primary term for the given shard.
         * See {@link IndexMetadata#primaryTerm(int)} for more information.
         */
        public Builder primaryTerm(int shardId, long primaryTerm) {
            if (primaryTerms == null) {
                initializePrimaryTerms();
            }
            this.primaryTerms[shardId] = primaryTerm;
            return this;
        }

        private void primaryTerms(long[] primaryTerms) {
            this.primaryTerms = primaryTerms.clone();
        }

        private void initializePrimaryTerms() {
            assert primaryTerms == null;
            if (numberOfShards() < 0) {
                throw new IllegalStateException("you must set the number of shards before setting/reading primary terms");
            }
            primaryTerms = new long[numberOfShards()];
            Arrays.fill(primaryTerms, SequenceNumbers.UNASSIGNED_PRIMARY_TERM);
        }

        public Builder system(boolean system) {
            this.isSystem = system;
            return this;
        }

        public boolean isSystem() {
            return isSystem;
        }

        public Builder context(Context context) {
            this.context = context;
            return this;
        }

        public Context context() {
            return context;
        }

        public IndexMetadata build() {
            final Map<String, AliasMetadata> tmpAliases = aliases;
            Settings tmpSettings = settings;

            /*
             * We expect that the metadata has been properly built to set the number of shards and the number of replicas, and do not rely
             * on the default values here. Those must have been set upstream.
             */
            if (INDEX_NUMBER_OF_SHARDS_SETTING.exists(settings) == false) {
                throw new IllegalArgumentException("must specify number of shards for index [" + index + "]");
            }
            final int numberOfShards = INDEX_NUMBER_OF_SHARDS_SETTING.get(settings);

            if (INDEX_NUMBER_OF_REPLICAS_SETTING.exists(settings) == false) {
                throw new IllegalArgumentException("must specify number of replicas for index [" + index + "]");
            }
            final int numberOfReplicas = INDEX_NUMBER_OF_REPLICAS_SETTING.get(settings);
            final int numberOfSearchReplicas = INDEX_NUMBER_OF_SEARCH_REPLICAS_SETTING.get(settings);

            int routingPartitionSize = INDEX_ROUTING_PARTITION_SIZE_SETTING.get(settings);
            if (routingPartitionSize != 1 && routingPartitionSize >= getRoutingNumShards()) {
                throw new IllegalArgumentException(
                    "routing partition size ["
                        + routingPartitionSize
                        + "] should be a positive number"
                        + " less than the number of shards ["
                        + getRoutingNumShards()
                        + "] for ["
                        + index
                        + "]"
                );
            }

            // fill missing slots in inSyncAllocationIds with empty set if needed and make all entries immutable
            final Map<Integer, Set<String>> filledInSyncAllocationIds = new HashMap<>();
            for (int i = 0; i < numberOfShards; i++) {
                if (inSyncAllocationIds.containsKey(i)) {
                    filledInSyncAllocationIds.put(i, Collections.unmodifiableSet(new HashSet<>(inSyncAllocationIds.get(i))));
                } else {
                    filledInSyncAllocationIds.put(i, Collections.emptySet());
                }
            }
            final Map<String, String> requireMap = INDEX_ROUTING_REQUIRE_GROUP_SETTING.getAsMap(settings);
            final DiscoveryNodeFilters requireFilters;
            if (requireMap.isEmpty()) {
                requireFilters = null;
            } else {
                requireFilters = DiscoveryNodeFilters.buildOrUpdateFromKeyValue(null, AND, requireMap);
            }
            Map<String, String> includeMap = INDEX_ROUTING_INCLUDE_GROUP_SETTING.getAsMap(settings);
            final DiscoveryNodeFilters includeFilters;
            if (includeMap.isEmpty()) {
                includeFilters = null;
            } else {
                includeFilters = DiscoveryNodeFilters.buildOrUpdateFromKeyValue(null, OR, includeMap);
            }
            Map<String, String> excludeMap = INDEX_ROUTING_EXCLUDE_GROUP_SETTING.getAsMap(settings);
            final DiscoveryNodeFilters excludeFilters;
            if (excludeMap.isEmpty()) {
                excludeFilters = null;
            } else {
                excludeFilters = DiscoveryNodeFilters.buildOrUpdateFromKeyValue(null, OR, excludeMap);
            }
            Map<String, String> initialRecoveryMap = INDEX_ROUTING_INITIAL_RECOVERY_GROUP_SETTING.getAsMap(settings);
            final DiscoveryNodeFilters initialRecoveryFilters;
            if (initialRecoveryMap.isEmpty()) {
                initialRecoveryFilters = null;
            } else {
                initialRecoveryFilters = DiscoveryNodeFilters.buildOrUpdateFromKeyValue(null, OR, initialRecoveryMap);
            }
            Version indexCreatedVersion = indexCreated(settings);
            Version indexUpgradedVersion = settings.getAsVersion(IndexMetadata.SETTING_VERSION_UPGRADED, indexCreatedVersion);

            if (primaryTerms == null) {
                initializePrimaryTerms();
            } else if (primaryTerms.length != numberOfShards) {
                throw new IllegalStateException(
                    "primaryTerms length is ["
                        + primaryTerms.length
                        + "] but should be equal to number of shards ["
                        + numberOfShards()
                        + "]"
                );
            }

            final ActiveShardCount waitForActiveShards = SETTING_WAIT_FOR_ACTIVE_SHARDS.get(settings);
            if (waitForActiveShards.validate(numberOfReplicas) == false) {
                throw new IllegalArgumentException(
                    "invalid "
                        + SETTING_WAIT_FOR_ACTIVE_SHARDS.getKey()
                        + "["
                        + waitForActiveShards
                        + "]: cannot be greater than "
                        + "number of shard copies ["
                        + (numberOfReplicas + 1)
                        + "]"
                );
            }

            final int indexTotalShardsPerNodeLimit = ShardsLimitAllocationDecider.INDEX_TOTAL_SHARDS_PER_NODE_SETTING.get(settings);

            final String uuid = settings.get(SETTING_INDEX_UUID, INDEX_UUID_NA_VALUE);

            return new IndexMetadata(
                new Index(index, uuid),
                version,
                mappingVersion,
                settingsVersion,
                aliasesVersion,
                primaryTerms,
                state,
                numberOfShards,
                numberOfReplicas,
                numberOfSearchReplicas,
                tmpSettings,
                mappings,
                tmpAliases,
                customMetadata,
                filledInSyncAllocationIds,
                requireFilters,
                initialRecoveryFilters,
                includeFilters,
                excludeFilters,
                indexCreatedVersion,
                indexUpgradedVersion,
                getRoutingNumShards(),
                routingPartitionSize,
                waitForActiveShards,
                rolloverInfos,
                isSystem,
                indexTotalShardsPerNodeLimit,
                context
            );
        }

        public static void toXContent(IndexMetadata indexMetadata, XContentBuilder builder, ToXContent.Params params) throws IOException {
            Metadata.XContentContext context = Metadata.XContentContext.valueOf(
                params.param(CONTEXT_MODE_PARAM, Metadata.CONTEXT_MODE_API)
            );

            builder.startObject(indexMetadata.getIndex().getName());

            builder.field(KEY_VERSION, indexMetadata.getVersion());
            builder.field(KEY_MAPPING_VERSION, indexMetadata.getMappingVersion());
            builder.field(KEY_SETTINGS_VERSION, indexMetadata.getSettingsVersion());
            builder.field(KEY_ALIASES_VERSION, indexMetadata.getAliasesVersion());
            builder.field(KEY_ROUTING_NUM_SHARDS, indexMetadata.getRoutingNumShards());

            builder.field(KEY_STATE, indexMetadata.getState().toString().toLowerCase(Locale.ENGLISH));

            boolean binary = params.paramAsBoolean("binary", false);

            builder.startObject(KEY_SETTINGS);
            if (context != Metadata.XContentContext.API) {
                indexMetadata.getSettings().toXContent(builder, new MapParams(Collections.singletonMap("flat_settings", "true")));
            } else {
                indexMetadata.getSettings().toXContent(builder, params);
            }
            builder.endObject();

            if (context != Metadata.XContentContext.API) {
                builder.startArray(KEY_MAPPINGS);
                MappingMetadata mmd = indexMetadata.mapping();
                if (mmd != null) {
                    if (binary) {
                        builder.value(mmd.source().compressed());
                    } else {
                        builder.map(XContentHelper.convertToMap(mmd.source().uncompressed(), true).v2());
                    }
                }
                builder.endArray();
            } else {
                builder.startObject(KEY_MAPPINGS);
                MappingMetadata mmd = indexMetadata.mapping();
                if (mmd != null) {
                    Map<String, Object> mapping = XContentHelper.convertToMap(mmd.source().uncompressed(), false).v2();
                    if (mapping.size() == 1 && mapping.containsKey(mmd.type())) {
                        // the type name is the root value, reduce it
                        mapping = (Map<String, Object>) mapping.get(mmd.type());
                    }
                    builder.field(mmd.type());
                    builder.map(mapping);
                }
                builder.endObject();
            }

            for (final Map.Entry<String, DiffableStringMap> cursor : indexMetadata.customData.entrySet()) {
                builder.field(cursor.getKey());
                builder.map(cursor.getValue());
            }

            if (context != Metadata.XContentContext.API) {
                builder.startObject(KEY_ALIASES);
                for (final AliasMetadata cursor : indexMetadata.getAliases().values()) {
                    AliasMetadata.Builder.toXContent(cursor, builder, params);
                }
                builder.endObject();

                builder.startArray(KEY_PRIMARY_TERMS);
                for (int i = 0; i < indexMetadata.getNumberOfShards(); i++) {
                    builder.value(indexMetadata.primaryTerm(i));
                }
                builder.endArray();
            } else {
                builder.startArray(KEY_ALIASES);
                for (final String cursor : indexMetadata.getAliases().keySet()) {
                    builder.value(cursor);
                }
                builder.endArray();

                builder.startObject(IndexMetadata.KEY_PRIMARY_TERMS);
                for (int shard = 0; shard < indexMetadata.getNumberOfShards(); shard++) {
                    builder.field(Integer.toString(shard), indexMetadata.primaryTerm(shard));
                }
                builder.endObject();
            }

            builder.startObject(KEY_IN_SYNC_ALLOCATIONS);
            for (final Map.Entry<Integer, Set<String>> cursor : indexMetadata.inSyncAllocationIds.entrySet()) {
                builder.startArray(String.valueOf(cursor.getKey()));
                for (String allocationId : cursor.getValue()) {
                    builder.value(allocationId);
                }
                builder.endArray();
            }
            builder.endObject();

            builder.startObject(KEY_ROLLOVER_INFOS);
            for (final RolloverInfo cursor : indexMetadata.getRolloverInfos().values()) {
                cursor.toXContent(builder, params);
            }
            builder.endObject();
            builder.field(KEY_SYSTEM, indexMetadata.isSystem);

            if (indexMetadata.context != null) {
                builder.field(CONTEXT_KEY);
                indexMetadata.context.toXContent(builder, params);
            }

            builder.endObject();
        }

        public static IndexMetadata fromXContent(XContentParser parser) throws IOException {
            if (parser.currentToken() == null) { // fresh parser? move to the first token
                parser.nextToken();
            }
            if (parser.currentToken() == XContentParser.Token.START_OBJECT) {  // on a start object move to next token
                parser.nextToken();
            }
            if (parser.currentToken() != XContentParser.Token.FIELD_NAME) {
                throw new IllegalArgumentException("expected field name but got a " + parser.currentToken());
            }
            Builder builder = new Builder(parser.currentName());

            String currentFieldName = null;
            XContentParser.Token token = parser.nextToken();
            if (token != XContentParser.Token.START_OBJECT) {
                throw new IllegalArgumentException("expected object but got a " + token);
            }
            boolean mappingVersion = false;
            boolean settingsVersion = false;
            boolean aliasesVersion = false;
            while ((token = parser.nextToken()) != XContentParser.Token.END_OBJECT) {
                if (token == XContentParser.Token.FIELD_NAME) {
                    currentFieldName = parser.currentName();
                } else if (token == XContentParser.Token.START_OBJECT) {
                    if (KEY_SETTINGS.equals(currentFieldName)) {
                        builder.settings(Settings.fromXContent(parser));
                    } else if (KEY_MAPPINGS.equals(currentFieldName)) {
                        while ((token = parser.nextToken()) != XContentParser.Token.END_OBJECT) {
                            if (token == XContentParser.Token.FIELD_NAME) {
                                currentFieldName = parser.currentName();
                            } else if (token == XContentParser.Token.START_OBJECT) {
                                String mappingType = currentFieldName;
                                Map<String, Object> mappingSource = MapBuilder.<String, Object>newMapBuilder()
                                    .put(mappingType, parser.mapOrdered())
                                    .map();
                                builder.putMapping(new MappingMetadata(mappingType, mappingSource));
                            } else {
                                throw new IllegalArgumentException("Unexpected token: " + token);
                            }
                        }
                    } else if (KEY_ALIASES.equals(currentFieldName)) {
                        while (parser.nextToken() != XContentParser.Token.END_OBJECT) {
                            builder.putAlias(AliasMetadata.Builder.fromXContent(parser));
                        }
                    } else if (KEY_IN_SYNC_ALLOCATIONS.equals(currentFieldName)) {
                        while ((token = parser.nextToken()) != XContentParser.Token.END_OBJECT) {
                            if (token == XContentParser.Token.FIELD_NAME) {
                                currentFieldName = parser.currentName();
                            } else if (token == XContentParser.Token.START_ARRAY) {
                                String shardId = currentFieldName;
                                Set<String> allocationIds = new HashSet<>();
                                while ((token = parser.nextToken()) != XContentParser.Token.END_ARRAY) {
                                    if (token == XContentParser.Token.VALUE_STRING) {
                                        allocationIds.add(parser.text());
                                    }
                                }
                                builder.putInSyncAllocationIds(Integer.valueOf(shardId), allocationIds);
                            } else {
                                throw new IllegalArgumentException("Unexpected token: " + token);
                            }
                        }
                    } else if (KEY_ROLLOVER_INFOS.equals(currentFieldName)) {
                        while ((token = parser.nextToken()) != XContentParser.Token.END_OBJECT) {
                            if (token == XContentParser.Token.FIELD_NAME) {
                                currentFieldName = parser.currentName();
                            } else if (token == XContentParser.Token.START_OBJECT) {
                                builder.putRolloverInfo(RolloverInfo.parse(parser, currentFieldName));
                            } else {
                                throw new IllegalArgumentException("Unexpected token: " + token);
                            }
                        }
                    } else if ("warmers".equals(currentFieldName)) {
                        // TODO: do this in 6.0:
                        // throw new IllegalArgumentException("Warmers are not supported anymore - are you upgrading from 1.x?");
                        // ignore: warmers have been removed in 5.0 and are
                        // simply ignored when upgrading from 2.x
                        assert Version.CURRENT.major <= 5;
                        parser.skipChildren();
                    } else if (CONTEXT_KEY.equals(currentFieldName)) {
                        builder.context(Context.fromXContent(parser));
                    } else {
                        // assume it's custom index metadata
                        builder.putCustom(currentFieldName, parser.mapStrings());
                    }
                } else if (token == XContentParser.Token.START_ARRAY) {
                    if (KEY_MAPPINGS.equals(currentFieldName)) {
                        while ((token = parser.nextToken()) != XContentParser.Token.END_ARRAY) {
                            if (token == XContentParser.Token.VALUE_EMBEDDED_OBJECT) {
                                builder.putMapping(new MappingMetadata(new CompressedXContent(parser.binaryValue())));
                            } else {
                                Map<String, Object> mapping = parser.mapOrdered();
                                if (mapping.size() == 1) {
                                    String mappingType = mapping.keySet().iterator().next();
                                    builder.putMapping(new MappingMetadata(mappingType, mapping));
                                }
                            }
                        }
                    } else if (KEY_PRIMARY_TERMS.equals(currentFieldName)) {
                        final List<Long> list = new ArrayList<>();
                        while ((token = parser.nextToken()) != XContentParser.Token.END_ARRAY) {
                            if (token == XContentParser.Token.VALUE_NUMBER) {
                                list.add(parser.longValue());
                            } else {
                                throw new IllegalStateException("found a non-numeric value under [" + KEY_PRIMARY_TERMS + "]");
                            }
                        }
                        builder.primaryTerms(list.stream().mapToLong(i -> i).toArray());
                    } else {
                        throw new IllegalArgumentException("Unexpected field for an array " + currentFieldName);
                    }
                } else if (token.isValue()) {
                    if (KEY_STATE.equals(currentFieldName)) {
                        builder.state(State.fromString(parser.text()));
                    } else if (KEY_VERSION.equals(currentFieldName)) {
                        builder.version(parser.longValue());
                    } else if (KEY_MAPPING_VERSION.equals(currentFieldName)) {
                        mappingVersion = true;
                        builder.mappingVersion(parser.longValue());
                    } else if (KEY_SETTINGS_VERSION.equals(currentFieldName)) {
                        settingsVersion = true;
                        builder.settingsVersion(parser.longValue());
                    } else if (KEY_ALIASES_VERSION.equals(currentFieldName)) {
                        aliasesVersion = true;
                        builder.aliasesVersion(parser.longValue());
                    } else if (KEY_ROUTING_NUM_SHARDS.equals(currentFieldName)) {
                        builder.setRoutingNumShards(parser.intValue());
                    } else if (KEY_SYSTEM.equals(currentFieldName)) {
                        builder.system(parser.booleanValue());
                    } else {
                        throw new IllegalArgumentException("Unexpected field [" + currentFieldName + "]");
                    }
                } else {
                    throw new IllegalArgumentException("Unexpected token " + token);
                }
            }
            // Reference:
            // https://github.com/opensearch-project/OpenSearch/blob/4dde0f2a3b445b2fc61dab29c5a2178967f4a3e3/server/src/main/java/org/opensearch/cluster/metadata/IndexMetadata.java#L1620-L1628
            Version legacyVersion = LegacyESVersion.fromId(6050099);
            if (Assertions.ENABLED && indexCreated(builder.settings).onOrAfter(legacyVersion)) {
                assert mappingVersion : "mapping version should be present for indices";
                assert settingsVersion : "settings version should be present for indices";
            }
            if (Assertions.ENABLED && indexCreated(builder.settings).onOrAfter(LegacyESVersion.V_7_2_0)) {
                assert aliasesVersion : "aliases version should be present for indices created on or after 7.2.0";
            }
            return builder.build();
        }
    }

    /**
     * Adds human readable version and creation date settings.
     * This method is used to display the settings in a human readable format in REST API
     */
    public static Settings addHumanReadableSettings(Settings settings) {
        Settings.Builder builder = Settings.builder().put(settings);
        Version version = SETTING_INDEX_VERSION_CREATED.get(settings);
        if (version != Version.V_EMPTY) {
            builder.put(SETTING_VERSION_CREATED_STRING, version.toString());
        }
        Version versionUpgraded = settings.getAsVersion(SETTING_VERSION_UPGRADED, null);
        if (versionUpgraded != null) {
            builder.put(SETTING_VERSION_UPGRADED_STRING, versionUpgraded.toString());
        }
        Long creationDate = settings.getAsLong(SETTING_CREATION_DATE, null);
        if (creationDate != null) {
            ZonedDateTime creationDateTime = ZonedDateTime.ofInstant(Instant.ofEpochMilli(creationDate), ZoneOffset.UTC);
            builder.put(SETTING_CREATION_DATE_STRING, creationDateTime.toString());
        }
        return builder.build();
    }

    private static final ToXContent.Params FORMAT_PARAMS;
    static {
        Map<String, String> params = new HashMap<>(2);
        params.put("binary", "true");
        params.put(Metadata.CONTEXT_MODE_PARAM, Metadata.CONTEXT_MODE_GATEWAY);
        FORMAT_PARAMS = new MapParams(params);
    }

    /**
     * Return the version the index was created from the provided index settings
     * <p>
     * This looks for the presence of the {@link Version} object with key {@link IndexMetadata#SETTING_VERSION_CREATED}
     */
    public static Version indexCreated(final Settings indexSettings) {
        final Version indexVersion = SETTING_INDEX_VERSION_CREATED.get(indexSettings);
        if (indexVersion.equals(Version.V_EMPTY)) {
            final String message = String.format(
                Locale.ROOT,
                "[%s] is not present in the index settings for index with UUID [%s]",
                SETTING_INDEX_VERSION_CREATED.getKey(),
                indexSettings.get(IndexMetadata.SETTING_INDEX_UUID)
            );
            throw new IllegalStateException(message);
        }
        return indexVersion;
    }

    /**
     * State format for {@link IndexMetadata} to write to and load from disk
     */
    public static final MetadataStateFormat<IndexMetadata> FORMAT = new MetadataStateFormat<>(INDEX_STATE_FILE_PREFIX) {

        @Override
        public void toXContent(XContentBuilder builder, IndexMetadata state) throws IOException {
            Builder.toXContent(state, builder, FORMAT_PARAMS);
        }

        @Override
        public IndexMetadata fromXContent(XContentParser parser) throws IOException {
            return Builder.fromXContent(parser);
        }
    };

    /**
     * Returns the number of shards that should be used for routing. This basically defines the hash space we use in
     * {@link org.opensearch.cluster.routing.OperationRouting#generateShardId(IndexMetadata, String, String)} to route documents
     * to shards based on their ID or their specific routing value. The default value is {@link #getNumberOfShards()}. This value only
     * changes if and index is shrunk.
     */
    public int getRoutingNumShards() {
        return routingNumShards;
    }

    /**
     * Returns the routing factor for this index. The default is {@code 1}.
     *
     * @see #getRoutingFactor(int, int) for details
     */
    public int getRoutingFactor() {
        return routingFactor;
    }

    /**
     * Returns the source shard ID to split the given target shard off
     * @param shardId the id of the target shard to split into
     * @param sourceIndexMetadata the source index metadata
     * @param numTargetShards the total number of shards in the target index
     * @return a the source shard ID to split off from
     */
    public static ShardId selectSplitShard(int shardId, IndexMetadata sourceIndexMetadata, int numTargetShards) {
        int numSourceShards = sourceIndexMetadata.getNumberOfShards();
        if (shardId >= numTargetShards) {
            throw new IllegalArgumentException(
                "the number of target shards (" + numTargetShards + ") must be greater than the shard id: " + shardId
            );
        }
        final int routingFactor = getRoutingFactor(numSourceShards, numTargetShards);
        assertSplitMetadata(numSourceShards, numTargetShards, sourceIndexMetadata);
        return new ShardId(sourceIndexMetadata.getIndex(), shardId / routingFactor);
    }

    /**
     * Returns the source shard ID to clone the given target shard off
     * @param shardId the id of the target shard to clone into
     * @param sourceIndexMetadata the source index metadata
     * @param numTargetShards the total number of shards in the target index
     * @return a the source shard ID to clone from
     */
    public static ShardId selectCloneShard(int shardId, IndexMetadata sourceIndexMetadata, int numTargetShards) {
        int numSourceShards = sourceIndexMetadata.getNumberOfShards();
        if (numSourceShards != numTargetShards) {
            throw new IllegalArgumentException(
                "the number of target shards ("
                    + numTargetShards
                    + ") must be the same as the number of"
                    + " source shards ("
                    + numSourceShards
                    + ")"
            );
        }
        return new ShardId(sourceIndexMetadata.getIndex(), shardId);
    }

    private static void assertSplitMetadata(int numSourceShards, int numTargetShards, IndexMetadata sourceIndexMetadata) {
        if (numSourceShards > numTargetShards) {
            throw new IllegalArgumentException(
                "the number of source shards ["
                    + numSourceShards
                    + "] must be less that the number of target shards ["
                    + numTargetShards
                    + "]"
            );
        }
        // now we verify that the numRoutingShards is valid in the source index
        // note: if the number of shards is 1 in the source index we can just assume it's correct since from 1 we can split into anything
        // this is important to special case here since we use this to validate this in various places in the code but allow to split form
        // 1 to N but we never modify the sourceIndexMetadata to accommodate for that
        int routingNumShards = numSourceShards == 1 ? numTargetShards : sourceIndexMetadata.getRoutingNumShards();
        if (routingNumShards % numTargetShards != 0) {
            throw new IllegalStateException(
                "the number of routing shards [" + routingNumShards + "] must be a multiple of the target shards [" + numTargetShards + "]"
            );
        }
        // this is just an additional assertion that ensures we are a factor of the routing num shards.
        assert sourceIndexMetadata.getNumberOfShards() == 1 // special case - we can split into anything from 1 shard
            || getRoutingFactor(numTargetShards, routingNumShards) >= 0;
    }

    /**
     * Selects the source shards for a local shard recovery. This might either be a split or a shrink operation.
     * @param shardId the target shard ID to select the source shards for
     * @param sourceIndexMetadata the source metadata
     * @param numTargetShards the number of target shards
     */
    public static Set<ShardId> selectRecoverFromShards(int shardId, IndexMetadata sourceIndexMetadata, int numTargetShards) {
        if (sourceIndexMetadata.getNumberOfShards() > numTargetShards) {
            return selectShrinkShards(shardId, sourceIndexMetadata, numTargetShards);
        } else if (sourceIndexMetadata.getNumberOfShards() < numTargetShards) {
            return Collections.singleton(selectSplitShard(shardId, sourceIndexMetadata, numTargetShards));
        } else {
            return Collections.singleton(selectCloneShard(shardId, sourceIndexMetadata, numTargetShards));
        }
    }

    /**
     * Returns the source shard ids to shrink into the given shard id.
     * @param shardId the id of the target shard to shrink to
     * @param sourceIndexMetadata the source index metadata
     * @param numTargetShards the total number of shards in the target index
     * @return a set of shard IDs to shrink into the given shard ID.
     */
    public static Set<ShardId> selectShrinkShards(int shardId, IndexMetadata sourceIndexMetadata, int numTargetShards) {
        if (shardId >= numTargetShards) {
            throw new IllegalArgumentException(
                "the number of target shards (" + numTargetShards + ") must be greater than the shard id: " + shardId
            );
        }
        if (sourceIndexMetadata.getNumberOfShards() < numTargetShards) {
            throw new IllegalArgumentException(
                "the number of target shards ["
                    + numTargetShards
                    + "] must be less that the number of source shards ["
                    + sourceIndexMetadata.getNumberOfShards()
                    + "]"
            );
        }
        int routingFactor = getRoutingFactor(sourceIndexMetadata.getNumberOfShards(), numTargetShards);
        Set<ShardId> shards = new HashSet<>(routingFactor);
        for (int i = shardId * routingFactor; i < routingFactor * shardId + routingFactor; i++) {
            shards.add(new ShardId(sourceIndexMetadata.getIndex(), i));
        }
        return shards;
    }

    /**
     * Returns the routing factor for and shrunk index with the given number of target shards.
     * This factor is used in the hash function in
     * {@link org.opensearch.cluster.routing.OperationRouting#generateShardId(IndexMetadata, String, String)} to guarantee consistent
     * hashing / routing of documents even if the number of shards changed (ie. a shrunk index).
     *
     * @param sourceNumberOfShards the total number of shards in the source index
     * @param targetNumberOfShards the total number of shards in the target index
     * @return the routing factor for and shrunk index with the given number of target shards.
     * @throws IllegalArgumentException if the number of source shards is less than the number of target shards or if the source shards
     * are not divisible by the number of target shards.
     */
    public static int getRoutingFactor(int sourceNumberOfShards, int targetNumberOfShards) {
        final int factor;
        if (sourceNumberOfShards < targetNumberOfShards) { // split
            factor = targetNumberOfShards / sourceNumberOfShards;
            if (factor * sourceNumberOfShards != targetNumberOfShards || factor <= 1) {
                throw new IllegalArgumentException(
                    "the number of source shards [" + sourceNumberOfShards + "] must be a " + "factor of [" + targetNumberOfShards + "]"
                );
            }
        } else if (sourceNumberOfShards > targetNumberOfShards) { // shrink
            factor = sourceNumberOfShards / targetNumberOfShards;
            if (factor * targetNumberOfShards != sourceNumberOfShards || factor <= 1) {
                throw new IllegalArgumentException(
                    "the number of source shards [" + sourceNumberOfShards + "] must be a " + "multiple of [" + targetNumberOfShards + "]"
                );
            }
        } else {
            factor = 1;
        }
        return factor;
    }

    /**
     * Parses the number from the rolled over index name. It also supports the date-math format (ie. index name is wrapped in &lt; and &gt;)
     * E.g.
     * - For ".ds-logs-000002" it will return 2
     * - For "&lt;logs-{now/d}-3&gt;" it'll return 3
     * @throws IllegalArgumentException if the index doesn't contain a "-" separator or if the last token after the separator is not a
     * number
     */
    public static int parseIndexNameCounter(String indexName) {
        int numberIndex = indexName.lastIndexOf("-");
        if (numberIndex == -1) {
            throw new IllegalArgumentException("no - separator found in index name [" + indexName + "]");
        }
        try {
            return Integer.parseInt(
                indexName.substring(numberIndex + 1, indexName.endsWith(">") ? indexName.length() - 1 : indexName.length())
            );
        } catch (NumberFormatException e) {
            throw new IllegalArgumentException("unable to parse the index name [" + indexName + "] to extract the counter", e);
        }
    }
}