/*
    * Copyright 2024 LINE Corporation
    *
    * LINE Corporation 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:
    *
    *   https://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.
   */
  
  package com.linecorp.centraldogma.server.management;
  
  import static java.util.Objects.requireNonNull;
  
  import java.io.File;
  import java.io.IOException;
  import java.nio.file.Files;
  import java.nio.file.Path;
  import java.util.Properties;
  import java.util.concurrent.Executor;
  import java.util.concurrent.Executors;
  
  import com.linecorp.armeria.common.util.ThreadFactories;
  
  /**
   * Manages the server status.
   */
  public final class ServerStatusManager {
  
      private static final String STATUS = "status";
  
      private final Executor sequentialExecutor =
              Executors.newSingleThreadExecutor(
                      ThreadFactories.newThreadFactory("server-status-manager", true));
  
      private final Path serverStatusFile;
  
      /**
       * Creates a new instance with the specified {@code dataDir}.
       */
      public ServerStatusManager(File dataDir) {
          requireNonNull(dataDir, "dataDir");
          final File serverStatusFile = new File(dataDir, "server-status.properties");
          // Create the file if it does not exist.
          try {
              serverStatusFile.createNewFile();
          } catch (IOException e) {
              throw new IllegalStateException("Failed to create server status file: " + serverStatusFile, e);
          }
          this.serverStatusFile = serverStatusFile.toPath();
      }
  
      /**
       * Reads the {@link ServerStatus} from the {@code "<data-dir>/server-status.properties"} file.
       *
       * <p>The stored {@link ServerStatus} may be used to determine whether the server is writable and
       * replicating when the server is started.
       */
      public ServerStatus serverStatus() {
          final Properties properties = new Properties();
          synchronized (serverStatusFile) {
              try {
                  properties.load(Files.newInputStream(serverStatusFile));
              } catch (IOException e) {
                  throw new IllegalStateException("Failed to load server status file: " + serverStatusFile, e);
              }
          }
  
          final String status = properties.getProperty(STATUS, "WRITABLE");
          return ServerStatus.valueOf(status);
      }
  
      /**
       * Updates the server status with the specified {@code writable} and {@code replicating} values.
       *
       * <p>The status may be stored in the {@code "<data-dir>/server-status.properties"} file so that the server
       * can be initialized with the same status when it is restarted.
       */
      public void updateStatus(ServerStatus newServerStatus) {
          synchronized (serverStatusFile) {
              final Properties properties = new Properties();
              try {
                  properties.load(Files.newInputStream(serverStatusFile));
              } catch (IOException e) {
                  throw new IllegalStateException("Failed to load server status file: " + serverStatusFile,
                                                  e);
              }
              properties.setProperty(STATUS, newServerStatus.name());
              try {
                  properties.store(Files.newOutputStream(serverStatusFile),
                                   "Do not edit this file manually. Use the AdministrativeService API.");
              } catch (IOException e) {
                  throw new IllegalStateException("Failed to store server status file: " + serverStatusFile,
                                                 e);
             }
         }
     }
 
     /**
      * Returns the {@link Executor} which is used to execute the status update sequentially.
      */
     public Executor sequentialExecutor() {
         return sequentialExecutor;
     }
 }