/*
 * Copyright Elasticsearch B.V. and/or licensed to Elasticsearch B.V. under one
 * or more contributor license agreements. Licensed under the "Elastic License
 * 2.0", the "GNU Affero General Public License v3.0 only", and the "Server Side
 * Public License v 1"; you may not use this file except in compliance with, at
 * your election, the "Elastic License 2.0", the "GNU Affero General Public
 * License v3.0 only", or the "Server Side Public License, v 1".
 */

package org.elasticsearch.plugins;

import org.elasticsearch.common.network.NetworkService;
import org.elasticsearch.common.settings.Settings;
import org.elasticsearch.discovery.SeedHostsProvider;
import org.elasticsearch.transport.TransportService;

import java.util.Collections;
import java.util.Map;
import java.util.function.Supplier;

/**
 * An additional extension point for {@link Plugin}s that extends Elasticsearch's discovery functionality. To add an additional
 * {@link NetworkService.CustomNameResolver} just implement the interface and implement the {@link #getCustomNameResolver(Settings)} method:
 *
 * <pre>{@code
 * public class MyDiscoveryPlugin extends Plugin implements DiscoveryPlugin {
 *     &#64;Override
 *     public NetworkService.CustomNameResolver getCustomNameResolver(Settings settings) {
 *         return new YourCustomNameResolverInstance(settings);
 *     }
 * }
 * }</pre>
 */
public interface DiscoveryPlugin {

    /**
     * Override to add additional {@link NetworkService.CustomNameResolver}s.
     * This can be handy if you want to provide your own Network interface name like _mycard_
     * and implement by yourself the logic to get an actual IP address/hostname based on this
     * name.
     *
     * For example: you could call a third party service (an API) to resolve _mycard_.
     * Then you could define in elasticsearch.yml settings like:
     *
     * <pre>{@code
     * network.host: _mycard_
     * }</pre>
     */
    default NetworkService.CustomNameResolver getCustomNameResolver(Settings settings) {
        return null;
    }

    /**
     * Returns providers of seed hosts for discovery.
     *
     * The key of the returned map is the name of the host provider
     * (see {@link org.elasticsearch.discovery.DiscoveryModule#DISCOVERY_SEED_PROVIDERS_SETTING}), and
     * the value is a supplier to construct the host provider when it is selected for use.
     *
     * @param transportService Use to form the {@link org.elasticsearch.common.transport.TransportAddress} portion
     *                         of a {@link org.elasticsearch.cluster.node.DiscoveryNode}
     * @param networkService Use to find the publish host address of the current node
     */
    default Map<String, Supplier<SeedHostsProvider>> getSeedHostProviders(
        TransportService transportService,
        NetworkService networkService
    ) {
        return Collections.emptyMap();
    }
}