/*
 * 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.common.settings;

import org.apache.logging.log4j.LogManager;
import org.apache.logging.log4j.Logger;
import org.apache.logging.log4j.message.ParameterizedMessage;
import org.apache.lucene.search.spell.LevenshteinDistance;
import org.apache.lucene.util.CollectionUtil;
import org.opensearch.ExceptionsHelper;
import org.opensearch.common.collect.Tuple;
import org.opensearch.common.regex.Regex;

import java.util.ArrayList;
import java.util.Collections;
import java.util.HashMap;
import java.util.HashSet;
import java.util.List;
import java.util.Locale;
import java.util.Map;
import java.util.Set;
import java.util.concurrent.CopyOnWriteArrayList;
import java.util.function.BiConsumer;
import java.util.function.Consumer;
import java.util.function.Function;
import java.util.function.Predicate;
import java.util.regex.Pattern;
import java.util.stream.Collectors;

/**
 * A basic setting service that can be used for per-index and per-cluster settings.
 * This service offers transactional application of updates settings.
 *
 * @opensearch.internal
 */
public abstract class AbstractScopedSettings {

    public static final String ARCHIVED_SETTINGS_PREFIX = "archived.";
    private static final Pattern KEY_PATTERN = Pattern.compile("^(?:[-\\w]+[.])*[-\\w]+$");
    private static final Pattern GROUP_KEY_PATTERN = Pattern.compile("^(?:[-\\w]+[.])+$");
    private static final Pattern AFFIX_KEY_PATTERN = Pattern.compile("^(?:[-\\w]+[.])+[*](?:[.][-\\w]+)+$");

    private final Logger logger;

    private final Settings settings;
    private final List<SettingUpdater<?>> settingUpdaters = new CopyOnWriteArrayList<>();
    private final Map<String, Setting<?>> complexMatchers;
    private final Map<String, Setting<?>> keySettings;
    private final Map<Setting<?>, SettingUpgrader<?>> settingUpgraders;
    private final Setting.Property scope;
    private Settings lastSettingsApplied;

    protected AbstractScopedSettings(
        final Settings settings,
        final Set<Setting<?>> settingsSet,
        final Set<SettingUpgrader<?>> settingUpgraders,
        final Setting.Property scope
    ) {
        this.logger = LogManager.getLogger(this.getClass());
        this.settings = settings;
        this.lastSettingsApplied = Settings.EMPTY;

        this.settingUpgraders = Collections.unmodifiableMap(
            settingUpgraders.stream().collect(Collectors.toMap(SettingUpgrader::getSetting, Function.identity()))
        );

        this.scope = scope;
        Map<String, Setting<?>> complexMatchers = new HashMap<>();
        Map<String, Setting<?>> keySettings = new HashMap<>();
        for (Setting<?> setting : settingsSet) {
            if (setting.getProperties().contains(scope) == false) {
                throw new SettingsException("Setting " + setting + " must be a " + scope + " setting but has: " + setting.getProperties());
            }
            validateSettingKey(setting);

            if (setting.hasComplexMatcher()) {
                Setting<?> overlappingSetting = findOverlappingSetting(setting, complexMatchers);
                if (overlappingSetting != null) {
                    throw new SettingsException(
                        "complex setting key: ["
                            + setting.getKey()
                            + "] overlaps existing setting key: ["
                            + overlappingSetting.getKey()
                            + "]"
                    );
                }
                complexMatchers.putIfAbsent(setting.getKey(), setting);
            } else {
                keySettings.putIfAbsent(setting.getKey(), setting);
            }
        }
        this.complexMatchers = complexMatchers;
        this.keySettings = keySettings;
    }

    /**
     *  Returns the list of setting updaters registered in this scope.
     * @return an unmodifiable view of the setting updaters
     */
    public List<SettingUpdater<?>> getSettingUpdaters() {
        return Collections.unmodifiableList(settingUpdaters);
    }

    protected void validateSettingKey(Setting<?> setting) {
        if (isValidKey(setting.getKey()) == false
            && (setting.isGroupSetting() && isValidGroupKey(setting.getKey()) || isValidAffixKey(setting.getKey())) == false
            || setting.getKey().endsWith(".0")) {
            throw new SettingsException("illegal settings key: [" + setting.getKey() + "]");
        }
    }

    protected AbstractScopedSettings(Settings nodeSettings, Settings scopeSettings, AbstractScopedSettings other, Logger logger) {
        this.logger = logger;
        this.settings = nodeSettings;
        this.lastSettingsApplied = scopeSettings;
        this.scope = other.scope;
        complexMatchers = other.complexMatchers;
        keySettings = other.keySettings;
        settingUpgraders = Collections.unmodifiableMap(new HashMap<>(other.settingUpgraders));
        settingUpdaters.addAll(other.settingUpdaters);
    }

    public boolean registerSetting(Setting<?> setting) {
        validateSettingKey(setting);
        if (setting.hasComplexMatcher()) {
            return setting != complexMatchers.putIfAbsent(setting.getKey(), setting);
        } else {
            return setting != keySettings.putIfAbsent(setting.getKey(), setting);
        }
    }

    public boolean unregisterSetting(Setting<?> setting) {
        if (setting.hasComplexMatcher()) {
            return setting != complexMatchers.remove(setting.getKey());
        } else {
            return setting != keySettings.remove(setting.getKey());
        }
    }

    /**
     * Returns <code>true</code> iff the given key is a valid settings key otherwise <code>false</code>
     */
    public static boolean isValidKey(String key) {
        return KEY_PATTERN.matcher(key).matches();
    }

    private static boolean isValidGroupKey(String key) {
        return GROUP_KEY_PATTERN.matcher(key).matches();
    }

    // pkg private for tests
    static boolean isValidAffixKey(String key) {
        return AFFIX_KEY_PATTERN.matcher(key).matches();
    }

    public Setting.Property getScope() {
        return this.scope;
    }

    /**
     * Validates the given settings by running it through all update listeners without applying it. This
     * method will not change any settings but will fail if any of the settings can't be applied.
     */
    public synchronized Settings validateUpdate(Settings settings) {
        final Settings current = Settings.builder().put(this.settings).put(settings).build();
        final Settings previous = Settings.builder().put(this.settings).put(this.lastSettingsApplied).build();
        List<RuntimeException> exceptions = new ArrayList<>();
        for (SettingUpdater<?> settingUpdater : settingUpdaters) {
            try {
                // ensure running this through the updater / dynamic validator
                // don't check if the value has changed we wanna test this anyways
                settingUpdater.getValue(current, previous);
            } catch (RuntimeException ex) {
                exceptions.add(ex);
                logger.debug(() -> new ParameterizedMessage("failed to prepareCommit settings for [{}]", settingUpdater), ex);
            }
        }
        // here we are exhaustive and record all settings that failed.
        ExceptionsHelper.rethrowAndSuppress(exceptions);
        return current;
    }

    /**
     * Applies the given settings to all the settings consumers or to none of them. The settings
     * will be merged with the node settings before they are applied while given settings override existing node
     * settings.
     * @param newSettings the settings to apply
     * @return the unmerged applied settings
    */
    public synchronized Settings applySettings(Settings newSettings) {
        if (lastSettingsApplied != null && newSettings.equals(lastSettingsApplied)) {
            // nothing changed in the settings, ignore
            return newSettings;
        }
        final Settings current = Settings.builder().put(this.settings).put(newSettings).build();
        final Settings previous = Settings.builder().put(this.settings).put(this.lastSettingsApplied).build();
        try {
            List<Runnable> applyRunnables = new ArrayList<>();
            for (SettingUpdater<?> settingUpdater : settingUpdaters) {
                try {
                    applyRunnables.add(settingUpdater.updater(current, previous));
                } catch (Exception ex) {
                    logger.warn(() -> new ParameterizedMessage("failed to prepareCommit settings for [{}]", settingUpdater), ex);
                    throw ex;
                }
            }
            for (Runnable settingUpdater : applyRunnables) {
                settingUpdater.run();
            }
        } catch (Exception ex) {
            logger.warn("failed to apply settings", ex);
            throw ex;
        }
        return lastSettingsApplied = newSettings;
    }

    /**
     * Adds a settings consumer with a predicate that is only evaluated at update time.
     * <p>
     * Note: Only settings registered in {@link SettingsModule} can be changed dynamically.
     * </p>
     * @param validator an additional validator that is only applied to updates of this setting.
     *                  This is useful to add additional validation to settings at runtime compared to at startup time.
     */
    public synchronized <T> void addSettingsUpdateConsumer(Setting<T> setting, Consumer<T> consumer, Consumer<T> validator) {
        if (setting != get(setting.getKey())) {
            throw new SettingsException("Setting is not registered for key [" + setting.getKey() + "]");
        }
        addSettingsUpdater(setting.newUpdater(consumer, logger, validator));
    }

    /**
     * Adds a settings consumer that is only executed if any setting in the supplied list of settings is changed. In that case all the
     * settings are specified in the argument are returned.
     * <p>
     * Also automatically adds empty consumers for all settings in order to activate logging
     */
    public synchronized void addSettingsUpdateConsumer(Consumer<Settings> consumer, List<? extends Setting<?>> settings) {
        addSettingsUpdater(Setting.groupedSettingsUpdater(consumer, settings));
    }

    /**
     * Adds a settings consumer that is only executed if any setting in the supplied list of settings is changed. In that case all the
     * settings are specified in the argument are returned.  The validator is run across all specified settings before the settings are
     * applied.
     * <p>
     * Also automatically adds empty consumers for all settings in order to activate logging
     */
    public synchronized void addSettingsUpdateConsumer(
        Consumer<Settings> consumer,
        List<? extends Setting<?>> settings,
        Consumer<Settings> validator
    ) {
        addSettingsUpdater(Setting.groupedSettingsUpdater(consumer, settings, validator));
    }

    /**
     * Adds a settings consumer for affix settings. Affix settings have a namespace associated to it that needs to be available to the
     * consumer in order to be processed correctly.
     */
    public synchronized <T> void addAffixUpdateConsumer(
        Setting.AffixSetting<T> setting,
        BiConsumer<String, T> consumer,
        BiConsumer<String, T> validator
    ) {
        ensureSettingIsRegistered(setting);
        addSettingsUpdater(setting.newAffixUpdater(consumer, logger, validator));
    }

    /**
     * Adds a affix settings consumer that accepts the values for two settings. The consumer is only notified if one or both settings change
     * and if the provided validator succeeded.
     * <p>
     * Note: Only settings registered in {@link SettingsModule} can be changed dynamically.
     * </p>
     * This method registers a compound updater that is useful if two settings are depending on each other.
     * The consumer is always provided with both values even if only one of the two changes.
     */
    public synchronized <A, B> void addAffixUpdateConsumer(
        Setting.AffixSetting<A> settingA,
        Setting.AffixSetting<B> settingB,
        BiConsumer<String, Tuple<A, B>> consumer,
        BiConsumer<String, Tuple<A, B>> validator
    ) {
        // it would be awesome to have a generic way to do that ie. a set of settings that map to an object with a builder
        // down the road this would be nice to have!
        ensureSettingIsRegistered(settingA);
        ensureSettingIsRegistered(settingB);
        SettingUpdater<Map<SettingUpdater<A>, A>> affixUpdaterA = settingA.newAffixUpdater((a, b) -> {}, logger, (a, b) -> {});
        SettingUpdater<Map<SettingUpdater<B>, B>> affixUpdaterB = settingB.newAffixUpdater((a, b) -> {}, logger, (a, b) -> {});

        addSettingsUpdater(new SettingUpdater<Map<String, Tuple<A, B>>>() {

            @Override
            public boolean hasChanged(Settings current, Settings previous) {
                return affixUpdaterA.hasChanged(current, previous) || affixUpdaterB.hasChanged(current, previous);
            }

            @Override
            public Map<String, Tuple<A, B>> getValue(Settings current, Settings previous) {
                Map<String, Tuple<A, B>> map = new HashMap<>();
                BiConsumer<String, A> aConsumer = (key, value) -> {
                    assert map.containsKey(key) == false : "duplicate key: " + key;
                    map.put(key, new Tuple<>(value, settingB.getConcreteSettingForNamespace(key).get(current)));
                };
                BiConsumer<String, B> bConsumer = (key, value) -> {
                    Tuple<A, B> abTuple = map.get(key);
                    if (abTuple != null) {
                        map.put(key, new Tuple<>(abTuple.v1(), value));
                    } else {
                        assert settingA.getConcreteSettingForNamespace(key)
                            .get(current)
                            .equals(settingA.getConcreteSettingForNamespace(key).get(previous)) : "expected: "
                                + settingA.getConcreteSettingForNamespace(key).get(current)
                                + " but was "
                                + settingA.getConcreteSettingForNamespace(key).get(previous);
                        map.put(key, new Tuple<>(settingA.getConcreteSettingForNamespace(key).get(current), value));
                    }
                };
                SettingUpdater<Map<SettingUpdater<A>, A>> affixUpdaterA = settingA.newAffixUpdater(aConsumer, logger, (a, b) -> {});
                SettingUpdater<Map<SettingUpdater<B>, B>> affixUpdaterB = settingB.newAffixUpdater(bConsumer, logger, (a, b) -> {});
                affixUpdaterA.apply(current, previous);
                affixUpdaterB.apply(current, previous);
                for (Map.Entry<String, Tuple<A, B>> entry : map.entrySet()) {
                    validator.accept(entry.getKey(), entry.getValue());
                }
                return Collections.unmodifiableMap(map);
            }

            @Override
            public void apply(Map<String, Tuple<A, B>> values, Settings current, Settings previous) {
                for (Map.Entry<String, Tuple<A, B>> entry : values.entrySet()) {
                    consumer.accept(entry.getKey(), entry.getValue());
                }
            }
        });
    }

    /**
     * Adds a affix settings consumer that accepts the settings for a group of settings. The consumer is only
     * notified if at least one of the settings change.
     * <p>
     * Note: Only settings registered in {@link SettingsModule} can be changed dynamically.
     * </p>
     */
    public synchronized void addAffixGroupUpdateConsumer(List<Setting.AffixSetting<?>> settings, BiConsumer<String, Settings> consumer) {
        List<SettingUpdater> affixUpdaters = new ArrayList<>(settings.size());
        for (Setting.AffixSetting<?> setting : settings) {
            ensureSettingIsRegistered(setting);
            affixUpdaters.add(setting.newAffixUpdater((a, b) -> {}, logger, (a, b) -> {}));
        }

        addSettingsUpdater(new SettingUpdater<Map<String, Settings>>() {

            @Override
            public boolean hasChanged(Settings current, Settings previous) {
                return affixUpdaters.stream().anyMatch(au -> au.hasChanged(current, previous));
            }

            @Override
            public Map<String, Settings> getValue(Settings current, Settings previous) {
                Set<String> namespaces = new HashSet<>();
                for (Setting.AffixSetting<?> setting : settings) {
                    SettingUpdater affixUpdaterA = setting.newAffixUpdater((k, v) -> namespaces.add(k), logger, (a, b) -> {});
                    affixUpdaterA.apply(current, previous);
                }
                Map<String, Settings> namespaceToSettings = new HashMap<>(namespaces.size());
                for (String namespace : namespaces) {
                    Set<String> concreteSettings = new HashSet<>(settings.size());
                    for (Setting.AffixSetting<?> setting : settings) {
                        concreteSettings.add(setting.getConcreteSettingForNamespace(namespace).getKey());
                    }
                    namespaceToSettings.put(namespace, current.filter(concreteSettings::contains));
                }
                return namespaceToSettings;
            }

            @Override
            public void apply(Map<String, Settings> values, Settings current, Settings previous) {
                for (Map.Entry<String, Settings> entry : values.entrySet()) {
                    consumer.accept(entry.getKey(), entry.getValue());
                }
            }
        });
    }

    private void ensureSettingIsRegistered(Setting.AffixSetting<?> setting) {
        final Setting<?> registeredSetting = this.complexMatchers.get(setting.getKey());
        if (setting != registeredSetting) {
            throw new SettingsException("Setting is not registered for key [" + setting.getKey() + "]");
        }
    }

    /**
     * Adds a settings consumer for affix settings. Affix settings have a namespace associated to it that needs to be available to the
     * consumer in order to be processed correctly. This consumer will get a namespace to value map instead of each individual namespace
     * and value as in {@link #addAffixUpdateConsumer(Setting.AffixSetting, BiConsumer, BiConsumer)}
     */
    public synchronized <T> void addAffixMapUpdateConsumer(
        Setting.AffixSetting<T> setting,
        Consumer<Map<String, T>> consumer,
        BiConsumer<String, T> validator
    ) {
        final Setting<?> registeredSetting = this.complexMatchers.get(setting.getKey());
        if (setting != registeredSetting) {
            throw new SettingsException("Setting is not registered for key [" + setting.getKey() + "]");
        }
        addSettingsUpdater(setting.newAffixMapUpdater(consumer, logger, validator));
    }

    synchronized void addSettingsUpdater(SettingUpdater<?> updater) {
        this.settingUpdaters.add(updater);
    }

    /**
     * Adds a settings consumer that accepts the values for two settings.
     * See {@link #addSettingsUpdateConsumer(Setting, Setting, BiConsumer, BiConsumer)} for details.
     */
    public synchronized <A, B> void addSettingsUpdateConsumer(Setting<A> a, Setting<B> b, BiConsumer<A, B> consumer) {
        addSettingsUpdateConsumer(a, b, consumer, (i, j) -> {});
    }

    /**
     * Adds a settings consumer that accepts the values for two settings. The consumer is only notified if one or both settings change
     * and if the provided validator succeeded.
     * <p>
     * Note: Only settings registered in {@link SettingsModule} can be changed dynamically.
     * </p>
     * This method registers a compound updater that is useful if two settings are depending on each other.
     * The consumer is always provided with both values even if only one of the two changes.
     */
    public synchronized <A, B> void addSettingsUpdateConsumer(
        Setting<A> a,
        Setting<B> b,
        BiConsumer<A, B> consumer,
        BiConsumer<A, B> validator
    ) {
        if (a != get(a.getKey())) {
            throw new SettingsException("Setting is not registered for key [" + a.getKey() + "]");
        }
        if (b != get(b.getKey())) {
            throw new SettingsException("Setting is not registered for key [" + b.getKey() + "]");
        }
        addSettingsUpdater(Setting.compoundUpdater(consumer, validator, a, b, logger));
    }

    /**
     * Adds a settings consumer.
     * <p>
     * Note: Only settings registered in {@link org.opensearch.cluster.ClusterModule} can be changed dynamically.
     * </p>
     */
    public synchronized <T> void addSettingsUpdateConsumer(Setting<T> setting, Consumer<T> consumer) {
        addSettingsUpdateConsumer(setting, consumer, (s) -> {});
    }

    /**
     * Validates that all settings are registered and valid.
     *
     * @param settings             the settings to validate
     * @param validateDependencies true if dependent settings should be validated
     * @see Setting#getSettingsDependencies(String)
     */
    public final void validate(final Settings settings, final boolean validateDependencies) {
        validate(settings, validateDependencies, false, false);
    }

    /**
     * Validates that all settings are registered and valid.
     *
     * @param settings                       the settings to validate
     * @param validateDependencies           true if dependent settings should be validated
     * @param validateInternalOrPrivateIndex true if internal index settings should be validated
     * @see Setting#getSettingsDependencies(String)
     */
    public final void validate(final Settings settings, final boolean validateDependencies, final boolean validateInternalOrPrivateIndex) {
        validate(settings, validateDependencies, false, false, validateInternalOrPrivateIndex);
    }

    /**
     * Validates that all settings are registered and valid.
     *
     * @param settings               the settings
     * @param validateDependencies   true if dependent settings should be validated
     * @param ignorePrivateSettings  true if private settings should be ignored during validation
     * @param ignoreArchivedSettings true if archived settings should be ignored during validation
     * @see Setting#getSettingsDependencies(String)
     */
    public final void validate(
        final Settings settings,
        final boolean validateDependencies,
        final boolean ignorePrivateSettings,
        final boolean ignoreArchivedSettings
    ) {
        validate(settings, validateDependencies, ignorePrivateSettings, ignoreArchivedSettings, false);
    }

    /**
     * Validates that all settings are registered and valid.
     *
     * @param settings                       the settings
     * @param validateDependencies           true if dependent settings should be validated
     * @param ignorePrivateSettings          true if private settings should be ignored during validation
     * @param ignoreArchivedSettings         true if archived settings should be ignored during validation
     * @param validateInternalOrPrivateIndex true if index internal settings should be validated
     * @see Setting#getSettingsDependencies(String)
     */
    public final void validate(
        final Settings settings,
        final boolean validateDependencies,
        final boolean ignorePrivateSettings,
        final boolean ignoreArchivedSettings,
        final boolean validateInternalOrPrivateIndex
    ) {
        final List<RuntimeException> exceptions = new ArrayList<>();
        for (final String key : settings.keySet()) { // settings iterate in deterministic fashion
            final Setting<?> setting = getRaw(key);
            if (((isPrivateSetting(key) || (setting != null && setting.isPrivateIndex())) && ignorePrivateSettings)) {
                continue;
            }
            if (key.startsWith(ARCHIVED_SETTINGS_PREFIX) && ignoreArchivedSettings) {
                continue;
            }
            try {
                validate(key, settings, validateDependencies, validateInternalOrPrivateIndex);
            } catch (final RuntimeException ex) {
                exceptions.add(ex);
            }
        }
        ExceptionsHelper.rethrowAndSuppress(exceptions);
    }

    /**
     * Validates that the settings is valid.
     *
     * @param key the key of the setting to validate
     * @param settings the settings
     * @param validateDependencies true if dependent settings should be validated
     * @throws SettingsException if the setting is invalid
     */
    void validate(final String key, final Settings settings, final boolean validateDependencies) {
        validate(key, settings, validateDependencies, false);
    }

    /**
     * Validates that the settings is valid.
     *
     * @param key                            the key of the setting to validate
     * @param settings                       the settings
     * @param validateDependencies           true if dependent settings should be validated
     * @param validateInternalOrPrivateIndex true if internal index settings should be validated
     * @throws SettingsException if the setting is invalid
     */
    void validate(
        final String key,
        final Settings settings,
        final boolean validateDependencies,
        final boolean validateInternalOrPrivateIndex
    ) {
        Setting setting = getRaw(key);
        if (setting == null) {
            LevenshteinDistance ld = new LevenshteinDistance();
            List<Tuple<Float, String>> scoredKeys = new ArrayList<>();
            for (String k : this.keySettings.keySet()) {
                float distance = ld.getDistance(key, k);
                if (distance > 0.7f) {
                    scoredKeys.add(new Tuple<>(distance, k));
                }
            }
            CollectionUtil.timSort(scoredKeys, (a, b) -> b.v1().compareTo(a.v1()));
            String msgPrefix = "unknown setting";
            SecureSettings secureSettings = settings.getSecureSettings();
            if (secureSettings != null && settings.getSecureSettings().getSettingNames().contains(key)) {
                msgPrefix = "unknown secure setting";
            }
            String msg = msgPrefix + " [" + key + "]";
            List<String> keys = scoredKeys.stream().map((a) -> a.v2()).collect(Collectors.toList());
            if (keys.isEmpty() == false) {
                msg += " did you mean " + (keys.size() == 1 ? "[" + keys.get(0) + "]" : "any of " + keys.toString()) + "?";
            } else {
                msg += " please check that any required plugins are installed, or check the breaking changes documentation for removed "
                    + "settings";
            }
            throw new SettingsException(msg);
        } else {
            Set<Setting.SettingDependency> settingsDependencies = setting.getSettingsDependencies(key);
            if (setting.hasComplexMatcher()) {
                setting = setting.getConcreteSetting(key);
            }
            if (validateDependencies && settingsDependencies.isEmpty() == false) {
                for (final Setting.SettingDependency settingDependency : settingsDependencies) {
                    final Setting<?> dependency = settingDependency.getSetting();
                    // validate the dependent setting is set
                    if (dependency.existsOrFallbackExists(settings) == false) {
                        final String message = String.format(
                            Locale.ROOT,
                            "missing required setting [%s] for setting [%s]",
                            dependency.getKey(),
                            setting.getKey()
                        );
                        throw new SettingsException(message);
                    }
                    // validate the dependent setting value
                    settingDependency.validate(setting.getKey(), setting.get(settings), dependency.get(settings));
                }
            }
            // the only time that validateInternalOrPrivateIndex should be true is if this call is coming via the update settings API
            if (validateInternalOrPrivateIndex) {
                if (setting.isInternalIndex()) {
                    throw new SettingsException(
                        "can not update internal setting [" + setting.getKey() + "]; this setting is managed via a dedicated API"
                    );
                } else if (setting.isPrivateIndex()) {
                    throw new SettingsException(
                        "can not update private setting [" + setting.getKey() + "]; this setting is managed by OpenSearch"
                    );
                }
            }
        }
        setting.get(settings);
    }

    /**
     * Transactional interface to update settings.
     * @see Setting
     * @param <T> the type of the value of the setting
     *
     * @opensearch.internal
     */
    public interface SettingUpdater<T> {

        /**
         * Returns true if this updaters setting has changed with the current update
         * @param current the current settings
         * @param previous the previous setting
         * @return true if this updaters setting has changed with the current update
         */
        boolean hasChanged(Settings current, Settings previous);

        /**
         * Returns the instance value for the current settings. This method is stateless and idempotent.
         * This method will throw an exception if the source of this value is invalid.
         */
        T getValue(Settings current, Settings previous);

        /**
         * Applies the given value to the updater. This methods will actually run the update.
         */
        void apply(T value, Settings current, Settings previous);

        /**
         * Updates this updaters value if it has changed.
         * @return <code>true</code> iff the value has been updated.
         */
        default boolean apply(Settings current, Settings previous) {
            if (hasChanged(current, previous)) {
                T value = getValue(current, previous);
                apply(value, current, previous);
                return true;
            }
            return false;
        }

        /**
         * Returns a callable runnable that calls {@link #apply(Object, Settings, Settings)} if the settings
         * actually changed. This allows to defer the update to a later point in time while keeping type safety.
         * If the value didn't change the returned runnable is a noop.
         */
        default Runnable updater(Settings current, Settings previous) {
            if (hasChanged(current, previous)) {
                T value = getValue(current, previous);
                return () -> { apply(value, current, previous); };
            }
            return () -> {};
        }
    }

    /**
     * Returns the {@link Setting} for the given key or <code>null</code> if the setting can not be found.
     */
    public final Setting<?> get(String key) {
        Setting<?> raw = getRaw(key);
        if (raw == null) {
            return null;
        }
        if (raw.hasComplexMatcher()) {
            return raw.getConcreteSetting(key);
        } else {
            return raw;
        }
    }

    private Setting<?> getRaw(String key) {
        Setting<?> setting = keySettings.get(key);
        if (setting != null) {
            return setting;
        }
        for (Map.Entry<String, Setting<?>> entry : complexMatchers.entrySet()) {
            if (entry.getValue().match(key)) {
                assert assertMatcher(key, 1);
                assert entry.getValue().hasComplexMatcher();
                return entry.getValue();
            }
        }
        return null;
    }

    private boolean assertMatcher(String key, int numComplexMatchers) {
        List<Setting<?>> list = new ArrayList<>();
        for (Map.Entry<String, Setting<?>> entry : complexMatchers.entrySet()) {
            if (entry.getValue().match(key)) {
                list.add(entry.getValue().getConcreteSetting(key));
            }
        }
        assert list.size() == numComplexMatchers : "Expected "
            + numComplexMatchers
            + " complex matchers to match key ["
            + key
            + "] but got: "
            + list.toString();
        return true;
    }

    /**
     * Returns <code>true</code> if the setting for the given key is dynamically updateable. Otherwise <code>false</code>.
     */
    public boolean isDynamicSetting(String key) {
        final Setting<?> setting = get(key);
        return setting != null && setting.isDynamic();
    }

    /**
     * Returns <code>true</code> if the setting for the given key is final. Otherwise <code>false</code>.
     */
    public boolean isFinalSetting(String key) {
        final Setting<?> setting = get(key);
        return setting != null && setting.isFinal();
    }

    /**
     * Returns <code>true</code> if the setting for the given key is unmodifiableOnRestore. Otherwise <code>false</code>.
     */
    public boolean isUnmodifiableOnRestoreSetting(String key) {
        final Setting<?> setting = get(key);
        return setting != null && setting.isUnmodifiableOnRestore();
    }

    /**
     * Returns a settings object that contains all settings that are not
     * already set in the given source. The diff contains either the default value for each
     * setting or the settings value in the given default settings.
     */
    public Settings diff(Settings source, Settings defaultSettings) {
        Settings.Builder builder = Settings.builder();
        for (Setting<?> setting : keySettings.values()) {
            setting.diff(builder, source, defaultSettings);
        }
        for (Setting<?> setting : complexMatchers.values()) {
            setting.diff(builder, source, defaultSettings);
        }
        return builder.build();
    }

    /**
     * Returns the value for the given setting.
     */
    public <T> T get(Setting<T> setting) {
        if (setting.getProperties().contains(scope) == false) {
            throw new SettingsException(
                "settings scope doesn't match the setting scope [" + this.scope + "] not in [" + setting.getProperties() + "]"
            );
        }
        if (get(setting.getKey()) == null) {
            throw new SettingsException("setting " + setting.getKey() + " has not been registered");
        }
        return setting.get(this.lastSettingsApplied, settings);
    }

    /**
     * Returns the value for the given setting if it is explicitly set,
     * otherwise will return null instead of default value
     **/
    public <T> T getOrNull(Setting<T> setting) {
        if (setting.getProperties().contains(scope) == false) {
            throw new SettingsException(
                "settings scope doesn't match the setting scope [" + this.scope + "] not in [" + setting.getProperties() + "]"
            );
        }
        if (get(setting.getKey()) == null) {
            throw new SettingsException("setting " + setting.getKey() + " has not been registered");
        }
        if (setting.exists(lastSettingsApplied)) {
            return setting.get(lastSettingsApplied);
        }
        if (setting.exists(settings)) {
            return setting.get(settings);
        }
        if (setting.fallbackSetting != null) {
            if (setting.fallbackSetting.exists(lastSettingsApplied)) {
                return setting.fallbackSetting.get(lastSettingsApplied);
            }
            if (setting.fallbackSetting.exists(settings)) {
                return setting.fallbackSetting.get(settings);
            }
        }
        return null;
    }

    /**
     * Updates a target settings builder with new, updated or deleted settings from a given settings builder.
     * <p>
     * Note: This method will only allow updates to dynamic settings. if a non-dynamic setting is updated an
     * {@link SettingsException} is thrown instead.
     * </p>
     *
     * @param toApply the new settings to apply
     * @param target the target settings builder that the updates are applied to. All keys that have explicit null value in toApply will be
     *        removed from this builder
     * @param updates a settings builder that holds all updates applied to target
     * @param type a free text string to allow better exceptions messages
     * @return <code>true</code> if the target has changed otherwise <code>false</code>
     */
    public boolean updateDynamicSettings(Settings toApply, Settings.Builder target, Settings.Builder updates, String type) {
        return updateSettings(toApply, target, updates, type, true);
    }

    /**
     * Updates a target settings builder with new, updated or deleted settings from a given settings builder.
     *
     * @param toApply the new settings to apply
     * @param target the target settings builder that the updates are applied to. All keys that have explicit null value in toApply will be
     *        removed from this builder
     * @param updates a settings builder that holds all updates applied to target
     * @param type a free text string to allow better exceptions messages
     * @return <code>true</code> if the target has changed otherwise <code>false</code>
     */
    public boolean updateSettings(Settings toApply, Settings.Builder target, Settings.Builder updates, String type) {
        return updateSettings(toApply, target, updates, type, false);
    }

    /**
     * Returns <code>true</code> if the given key is a valid delete key
     */
    private boolean isValidDelete(String key, boolean onlyDynamic) {
        return isFinalSetting(key) == false && // it's not a final setting
            (onlyDynamic && isDynamicSetting(key)  // it's a dynamicSetting and we only do dynamic settings
                || get(key) == null && key.startsWith(ARCHIVED_SETTINGS_PREFIX) // the setting is not registered AND it's been archived
                || (onlyDynamic == false && get(key) != null)); // if it's not dynamic AND we have a key
    }

    /**
     * Updates a target settings builder with new, updated or deleted settings from a given settings builder.
     *
     * @param toApply the new settings to apply
     * @param target the target settings builder that the updates are applied to. All keys that have explicit null value in toApply will be
     *        removed from this builder
     * @param updates a settings builder that holds all updates applied to target
     * @param type a free text string to allow better exceptions messages
     * @param onlyDynamic if <code>false</code> all settings are updated otherwise only dynamic settings are updated. if set to
     *        <code>true</code> and a non-dynamic setting is updated an exception is thrown.
     * @return <code>true</code> if the target has changed otherwise <code>false</code>
     */
    private boolean updateSettings(Settings toApply, Settings.Builder target, Settings.Builder updates, String type, boolean onlyDynamic) {
        boolean changed = false;
        final Set<String> toRemove = new HashSet<>();
        Settings.Builder settingsBuilder = Settings.builder();
        final Predicate<String> canUpdate = (key) -> (isFinalSetting(key) == false && // it's not a final setting
            ((onlyDynamic == false && get(key) != null) || isDynamicSetting(key)));
        for (String key : toApply.keySet()) {
            boolean isDelete = toApply.hasValue(key) == false;
            if (isDelete && (isValidDelete(key, onlyDynamic) || key.endsWith("*"))) {
                // this either accepts null values that suffice the canUpdate test OR wildcard expressions (key ends with *)
                // we don't validate if there is any dynamic setting with that prefix yet we could do in the future
                toRemove.add(key);
                // we don't set changed here it's set after we apply deletes below if something actually changed
            } else if (get(key) == null) {
                throw new SettingsException(type + " setting [" + key + "], not recognized");
            } else if (isDelete == false && canUpdate.test(key)) {
                get(key).validateWithoutDependencies(toApply); // we might not have a full picture here do to a dependency validation
                settingsBuilder.copy(key, toApply);
                updates.copy(key, toApply);
                changed |= toApply.get(key).equals(target.get(key)) == false;
            } else {
                if (isFinalSetting(key)) {
                    throw new SettingsException("final " + type + " setting [" + key + "], not updateable");
                } else {
                    throw new SettingsException(type + " setting [" + key + "], not dynamically updateable");
                }
            }
        }
        changed |= applyDeletes(toRemove, target, k -> isValidDelete(k, onlyDynamic));
        target.put(settingsBuilder.build());
        return changed;
    }

    private static boolean applyDeletes(Set<String> deletes, Settings.Builder builder, Predicate<String> canRemove) {
        boolean changed = false;
        for (String entry : deletes) {
            Set<String> keysToRemove = new HashSet<>();
            Set<String> keySet = builder.keys();
            for (String key : keySet) {
                if (Regex.simpleMatch(entry, key) && canRemove.test(key)) {
                    // we have to re-check with canRemove here since we might have a wildcard expression foo.* that matches
                    // dynamic as well as static settings if that is the case we might remove static settings since we resolve the
                    // wildcards late
                    keysToRemove.add(key);
                }
            }
            for (String key : keysToRemove) {
                builder.remove(key);
                changed = true;
            }
        }
        return changed;
    }

    private static Setting<?> findOverlappingSetting(Setting<?> newSetting, Map<String, Setting<?>> complexMatchers) {
        assert newSetting.hasComplexMatcher();
        if (complexMatchers.containsKey(newSetting.getKey())) {
            // we return null here because we use a putIfAbsent call when inserting into the map, so if it exists then we already checked
            // the setting to make sure there are no overlapping settings.
            return null;
        }

        for (Setting<?> existingSetting : complexMatchers.values()) {
            if (newSetting.match(existingSetting.getKey()) || existingSetting.match(newSetting.getKey())) {
                return existingSetting;
            }
        }
        return null;
    }

    /**
     * Upgrade all settings eligible for upgrade in the specified settings instance.
     *
     * @param settings the settings instance that might contain settings to be upgraded
     * @return a new settings instance if any settings required upgrade, otherwise the same settings instance as specified
     */
    public Settings upgradeSettings(final Settings settings) {
        final Settings.Builder builder = Settings.builder();
        boolean changed = false; // track if any settings were upgraded
        for (final String key : settings.keySet()) {
            final Setting<?> setting = getRaw(key);
            final SettingUpgrader<?> upgrader = settingUpgraders.get(setting);
            if (upgrader == null) {
                // the setting does not have an upgrader, copy the setting
                builder.copy(key, settings);
            } else {
                // the setting has an upgrader, so mark that we have changed a setting and apply the upgrade logic
                changed = true;
                // noinspection ConstantConditions
                if (setting.getConcreteSetting(key).isListSetting()) {
                    final List<String> value = settings.getAsList(key);
                    final String upgradedKey = upgrader.getKey(key);
                    final List<String> upgradedValue = upgrader.getListValue(value);
                    builder.putList(upgradedKey, upgradedValue);
                } else {
                    final String value = settings.get(key);
                    final String upgradedKey = upgrader.getKey(key);
                    final String upgradedValue = upgrader.getValue(value);
                    builder.put(upgradedKey, upgradedValue);
                }
            }
        }
        // we only return a new instance if there was an upgrade
        return changed ? builder.build() : settings;
    }

    /**
     * Archives invalid or unknown settings. Any setting that is not recognized or fails validation
     * will be archived. This means the setting is prefixed with {@value ARCHIVED_SETTINGS_PREFIX}
     * and remains in the settings object. This can be used to detect invalid settings via APIs.
     *
     * @param settings        the {@link Settings} instance to scan for unknown or invalid settings
     * @param unknownConsumer callback on unknown settings (consumer receives unknown key and its
     *                        associated value)
     * @param invalidConsumer callback on invalid settings (consumer receives invalid key, its
     *                        associated value and an exception)
     * @return a {@link Settings} instance with the unknown or invalid settings archived
     */
    public Settings archiveUnknownOrInvalidSettings(
        final Settings settings,
        final Consumer<Map.Entry<String, String>> unknownConsumer,
        final BiConsumer<Map.Entry<String, String>, IllegalArgumentException> invalidConsumer
    ) {
        Settings.Builder builder = Settings.builder();
        boolean changed = false;
        for (String key : settings.keySet()) {
            try {
                Setting<?> setting = get(key);
                if (setting != null) {
                    setting.get(settings);
                    builder.copy(key, settings);
                } else {
                    if (key.startsWith(ARCHIVED_SETTINGS_PREFIX) || isPrivateSetting(key)) {
                        builder.copy(key, settings);
                    } else {
                        changed = true;
                        unknownConsumer.accept(new Entry(key, settings));
                        /*
                         * We put them back in here such that tools can check from the outside if there are any indices with invalid
                         * settings. The setting can remain there but we want users to be aware that some of their setting are invalid and
                         * they can research why and what they need to do to replace them.
                         */
                        builder.copy(ARCHIVED_SETTINGS_PREFIX + key, key, settings);
                    }
                }
            } catch (IllegalArgumentException ex) {
                changed = true;
                invalidConsumer.accept(new Entry(key, settings), ex);
                /*
                 * We put them back in here such that tools can check from the outside if there are any indices with invalid settings. The
                 * setting can remain there but we want users to be aware that some of their setting are invalid and they can research why
                 * and what they need to do to replace them.
                 */
                builder.copy(ARCHIVED_SETTINGS_PREFIX + key, key, settings);
            }
        }
        if (changed) {
            return builder.build();
        } else {
            return settings;
        }
    }

    private static final class Entry implements Map.Entry<String, String> {

        private final String key;
        private final Settings settings;

        private Entry(String key, Settings settings) {
            this.key = key;
            this.settings = settings;
        }

        @Override
        public String getKey() {
            return key;
        }

        @Override
        public String getValue() {
            return settings.get(key);
        }

        @Override
        public String setValue(String value) {
            throw new UnsupportedOperationException();
        }
    }

    /**
     * Returns <code>true</code> iff the setting is a private setting ie. it should be treated as valid even though it has no internal
     * representation. Otherwise <code>false</code>
     */
    // TODO this should be replaced by Setting.Property.HIDDEN or something like this.
    public boolean isPrivateSetting(String key) {
        return false;
    }

}
