/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements. See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF 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.
 */

package org.apache.ozone.lib.servlet;

import java.net.InetAddress;
import java.net.InetSocketAddress;
import java.net.UnknownHostException;
import java.text.MessageFormat;
import javax.servlet.ServletContextEvent;
import javax.servlet.ServletContextListener;
import org.apache.hadoop.hdds.annotation.InterfaceAudience;
import org.apache.ozone.lib.server.Server;
import org.apache.ozone.lib.server.ServerException;

/**
 * {@link Server} subclass that implements <code>ServletContextListener</code>
 * and uses its lifecycle to start and stop the server.
 */
@InterfaceAudience.Private
public abstract class ServerWebApp
       extends Server
       implements ServletContextListener {

  private static final String HOME_DIR = ".home.dir";
  private static final String CONFIG_DIR = ".config.dir";
  private static final String LOG_DIR = ".log.dir";
  private static final String TEMP_DIR = ".temp.dir";
  private static final String HTTP_HOSTNAME = ".http.hostname";
  private static final String HTTP_PORT = ".http.port";

  private static final ThreadLocal<String> HOME_DIR_TL =
      new ThreadLocal<String>();

  private InetSocketAddress authority;

  /**
   * Constructor. Subclasses must have a default constructor specifying
   * the server name.
   * <p>
   * The server name is used to resolve the Java System properties that define
   * the server home, config, log and temp directories.
   * <p>
   * The home directory is looked in the Java System property
   * <code>#SERVER_NAME#.home.dir</code>.
   * <p>
   * The config directory is looked in the Java System property
   * <code>#SERVER_NAME#.config.dir</code>, if not defined it resolves to
   * the <code>#SERVER_HOME_DIR#/conf</code> directory.
   * <p>
   * The log directory is looked in the Java System property
   * <code>#SERVER_NAME#.log.dir</code>, if not defined it resolves to
   * the <code>#SERVER_HOME_DIR#/log</code> directory.
   * <p>
   * The temp directory is looked in the Java System property
   * <code>#SERVER_NAME#.temp.dir</code>, if not defined it resolves to
   * the <code>#SERVER_HOME_DIR#/temp</code> directory.
   *
   * @param name server name.
   */
  public ServerWebApp(String name) {
    super(name, getHomeDir(name),
          getDir(name, CONFIG_DIR, getHomeDir(name) + "/conf"),
          getDir(name, LOG_DIR, getHomeDir(name) + "/log"),
          getDir(name, TEMP_DIR, getHomeDir(name) + "/temp"), null);
  }

  /**
   * Returns the server home directory.
   * <p>
   * It is looked up in the Java System property
   * <code>#SERVER_NAME#.home.dir</code>.
   *
   * @param name the server home directory.
   *
   * @return the server home directory.
   */
  static String getHomeDir(String name) {
    String homeDir = HOME_DIR_TL.get();
    if (homeDir == null) {
      String sysProp = name + HOME_DIR;
      homeDir = System.getProperty(sysProp);
      if (homeDir == null) {
        throw new IllegalArgumentException(MessageFormat.format(
            "System property [{0}] not defined", sysProp));
      }
    }
    return homeDir;
  }

  /**
   * Convenience method that looks for Java System property defining a
   * diretory and if not present defaults to the specified directory.
   *
   * @param name server name, used as prefix of the Java System property.
   * @param dirType dir type, use as postfix of the Java System property.
   * @param defaultDir the default directory to return if the Java System
   * property <code>name + dirType</code> is not defined.
   *
   * @return the directory defined in the Java System property or the
   *         the default directory if the Java System property is not defined.
   */
  static String getDir(String name, String dirType, String defaultDir) {
    String sysProp = name + dirType;
    return System.getProperty(sysProp, defaultDir);
  }

  /**
   * Initializes the <code>ServletContextListener</code> which initializes
   * the Server.
   *
   * @param event servelt context event.
   */
  @Override
  public void contextInitialized(ServletContextEvent event) {
    try {
      init();
    } catch (ServerException ex) {
      event.getServletContext().log("ERROR: " + ex.getMessage());
      throw new RuntimeException(ex);
    }
  }

  /**
   * Resolves the host and port InetSocketAddress the
   * web server is listening to.
   * <p>
   * This implementation looks for the following 2 properties:
   * <ul>
   *   <li>#SERVER_NAME#.http.hostname</li>
   *   <li>#SERVER_NAME#.http.port</li>
   * </ul>
   *
   * @return the host and port InetSocketAddress the
   *         web server is listening to.
   * @throws ServerException thrown
   *         if any of the above 2 properties is not defined.
   */
  protected InetSocketAddress resolveAuthority() throws ServerException {
    String hostnameKey = getName() + HTTP_HOSTNAME;
    String portKey = getName() + HTTP_PORT;
    String host = System.getProperty(hostnameKey);
    String port = System.getProperty(portKey);
    if (host == null) {
      throw new ServerException(ServerException.ERROR.S13, hostnameKey);
    }
    if (port == null) {
      throw new ServerException(ServerException.ERROR.S13, portKey);
    }
    try {
      InetAddress add = InetAddress.getByName(host);
      int portNum = Integer.parseInt(port);
      return new InetSocketAddress(add, portNum);
    } catch (UnknownHostException ex) {
      throw new ServerException(ServerException.ERROR.S14, ex.toString(), ex);
    }
  }

  /**
   * Destroys the <code>ServletContextListener</code> which destroys
   * the Server.
   *
   * @param event servelt context event.
   */
  @Override
  public void contextDestroyed(ServletContextEvent event) {
    destroy();
  }

  /**
   * Returns the hostname:port InetSocketAddress the webserver is listening to.
   *
   * @return the hostname:port InetSocketAddress the webserver is listening to.
   */
  public InetSocketAddress getAuthority() throws ServerException {
    synchronized (this) {
      if (authority == null) {
        authority = resolveAuthority();
      }
      return authority;
    }
  }
}
