/*
 * Copyright ConsenSys AG.
 *
 * Licensed 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.
 *
 * SPDX-License-Identifier: Apache-2.0
 */
package org.hyperledger.besu.plugin;

import java.util.Optional;
import java.util.concurrent.CompletableFuture;

/**
 * Base interface for Besu plugins.
 *
 * <p>Plugins are discovered and loaded using {@link java.util.ServiceLoader} from jar files within
 * Besu's plugin directory. See the {@link java.util.ServiceLoader} documentation for how to
 * register plugins.
 */
public interface BesuPlugin {

  /**
   * Returns the name of the plugin. This name is used to trigger specific actions on individual
   * plugins.
   *
   * @return an {@link Optional} wrapping the unique name of the plugin.
   */
  default Optional<String> getName() {
    return Optional.of(this.getClass().getName());
  }

  /**
   * Called when the plugin is first registered with Besu. Plugins are registered very early in the
   * Besu life-cycle and should use this callback to register any command line options required via
   * the PicoCLIOptions service.
   *
   * <p>The <code>context</code> parameter should be stored in a field in the plugin. This is the
   * only time it will be provided to the plugin and is how the plugin will interact with Besu.
   *
   * <p>Typically the plugin will not begin operation until the {@link #start()} method is called.
   *
   * @param context the context that provides access to Besu services.
   */
  void register(BesuContext context);

  /**
   * Called once when besu has loaded configuration but before external services have been started
   * e.g. metrics and http
   */
  default void beforeExternalServices() {}

  /**
   * Called once Besu has loaded configuration and has started external services but before the main
   * loop is up. The plugin should begin operation, including registering any event listener with
   * Besu services and starting any background threads the plugin requires.
   */
  void start();

  /**
   * Called when the plugin is being reloaded. This method will be called through a dedicated JSON
   * RPC endpoint. If not overridden this method does nothing for convenience. The plugin should
   * only implement this method if it supports dynamic reloading.
   *
   * <p>The plugin should reload its configuration dynamically or do nothing if not applicable.
   *
   * @return a {@link CompletableFuture}
   */
  default CompletableFuture<Void> reloadConfiguration() {
    return CompletableFuture.completedFuture(null);
  }

  /**
   * Called when the plugin is being stopped. This method will be called as part of Besu shutting
   * down but may also be called at other times to disable the plugin.
   *
   * <p>The plugin should remove any registered listeners and stop any background threads it
   * started.
   */
  void stop();
}
