/**
 * 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.hadoop.fs.sftp;

import java.io.IOException;
import java.util.HashMap;
import java.util.HashSet;
import java.util.Iterator;
import java.util.Set;

import org.apache.hadoop.util.StringUtils;

import com.jcraft.jsch.ChannelSftp;
import com.jcraft.jsch.JSch;
import com.jcraft.jsch.JSchException;
import com.jcraft.jsch.Session;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

/** Concurrent/Multiple Connections. */
class SFTPConnectionPool {

  public static final Logger LOG =
      LoggerFactory.getLogger(SFTPFileSystem.class);
  // Maximum number of allowed live connections. This doesn't mean we cannot
  // have more live connections. It means that when we have more
  // live connections than this threshold, any unused connection will be
  // closed.
  private int maxConnection;
  private int liveConnectionCount = 0;
  private HashMap<ConnectionInfo, HashSet<ChannelSftp>> idleConnections =
      new HashMap<ConnectionInfo, HashSet<ChannelSftp>>();
  private HashMap<ChannelSftp, ConnectionInfo> con2infoMap =
      new HashMap<ChannelSftp, ConnectionInfo>();

  SFTPConnectionPool(int maxConnection) {
    this.maxConnection = maxConnection;
  }

  synchronized ChannelSftp getFromPool(ConnectionInfo info) throws IOException {
    Set<ChannelSftp> cons = idleConnections.get(info);
    ChannelSftp channel;

    if (cons != null && cons.size() > 0) {
      Iterator<ChannelSftp> it = cons.iterator();
      if (it.hasNext()) {
        channel = it.next();
        idleConnections.remove(info);
        return channel;
      } else {
        throw new IOException("Connection pool error.");
      }
    }
    return null;
  }

  /** Add the channel into pool.
   * @param channel
   */
  synchronized void returnToPool(ChannelSftp channel) {
    ConnectionInfo info = con2infoMap.get(channel);
    HashSet<ChannelSftp> cons = idleConnections.get(info);
    if (cons == null) {
      cons = new HashSet<>();
      idleConnections.put(info, cons);
    }
    cons.add(channel);

  }

  /** Shutdown the connection pool and close all open connections. */
  synchronized void shutdown() {
    if (this.con2infoMap == null){
      return; // already shutdown in case it is called
    }
    LOG.info("Inside shutdown, con2infoMap size=" + con2infoMap.size());

    this.maxConnection = 0;
    Set<ChannelSftp> cons = con2infoMap.keySet();
    if (cons != null && cons.size() > 0) {
      // make a copy since we need to modify the underlying Map
      Set<ChannelSftp> copy = new HashSet<>(cons);
      // Initiate disconnect from all outstanding connections
      for (ChannelSftp con : copy) {
        try {
          disconnect(con);
        } catch (IOException ioe) {
          ConnectionInfo info = con2infoMap.get(con);
          LOG.error(
              "Error encountered while closing connection to " + info.getHost(),
              ioe);
        }
      }
    }
    // make sure no further connections can be returned.
    this.idleConnections = null;
    this.con2infoMap = null;
  }

  public synchronized int getMaxConnection() {
    return maxConnection;
  }

  public synchronized void setMaxConnection(int maxConn) {
    this.maxConnection = maxConn;
  }

  public ChannelSftp connect(String host, int port, String user,
      String password, String keyFile) throws IOException {
    // get connection from pool
    ConnectionInfo info = new ConnectionInfo(host, port, user);
    ChannelSftp channel = getFromPool(info);

    if (channel != null) {
      if (channel.isConnected()) {
        return channel;
      } else {
        channel = null;
        synchronized (this) {
          --liveConnectionCount;
          con2infoMap.remove(channel);
        }
      }
    }

    // create a new connection and add to pool
    JSch jsch = new JSch();
    Session session = null;
    try {
      if (user == null || user.length() == 0) {
        user = System.getProperty("user.name");
      }

      if (password == null) {
        password = "";
      }

      if (keyFile != null && keyFile.length() > 0) {
        jsch.addIdentity(keyFile);
      }

      if (port <= 0) {
        session = jsch.getSession(user, host);
      } else {
        session = jsch.getSession(user, host, port);
      }

      session.setPassword(password);

      java.util.Properties config = new java.util.Properties();
      config.put("StrictHostKeyChecking", "no");
      session.setConfig(config);

      session.connect();
      channel = (ChannelSftp) session.openChannel("sftp");
      channel.connect();

      synchronized (this) {
        con2infoMap.put(channel, info);
        liveConnectionCount++;
      }

      return channel;

    } catch (JSchException e) {
      throw new IOException(StringUtils.stringifyException(e));
    }
  }

  void disconnect(ChannelSftp channel) throws IOException {
    if (channel != null) {
      // close connection if too many active connections
      boolean closeConnection = false;
      synchronized (this) {
        if (liveConnectionCount > maxConnection) {
          --liveConnectionCount;
          con2infoMap.remove(channel);
          closeConnection = true;
        }
      }
      if (closeConnection) {
        if (channel.isConnected()) {
          try {
            Session session = channel.getSession();
            channel.disconnect();
            session.disconnect();
          } catch (JSchException e) {
            throw new IOException(StringUtils.stringifyException(e));
          }
        }

      } else {
        returnToPool(channel);
      }
    }
  }

  public int getIdleCount() {
    return this.idleConnections.size();
  }

  public int getLiveConnCount() {
    return this.liveConnectionCount;
  }

  public int getConnPoolSize() {
    return this.con2infoMap.size();
  }

  /**
   * Class to capture the minimal set of information that distinguish
   * between different connections.
   */
  static class ConnectionInfo {
    private String host = "";
    private int port;
    private String user = "";

    ConnectionInfo(String hst, int prt, String usr) {
      this.host = hst;
      this.port = prt;
      this.user = usr;
    }

    public String getHost() {
      return host;
    }

    public void setHost(String hst) {
      this.host = hst;
    }

    public int getPort() {
      return port;
    }

    public void setPort(int prt) {
      this.port = prt;
    }

    public String getUser() {
      return user;
    }

    public void setUser(String usr) {
      this.user = usr;
    }

    @Override
    public boolean equals(Object obj) {
      if (this == obj) {
        return true;
      }

      if (obj instanceof ConnectionInfo) {
        ConnectionInfo con = (ConnectionInfo) obj;

        boolean ret = true;
        if (this.host == null || !this.host.equalsIgnoreCase(con.host)) {
          ret = false;
        }
        if (this.port >= 0 && this.port != con.port) {
          ret = false;
        }
        if (this.user == null || !this.user.equalsIgnoreCase(con.user)) {
          ret = false;
        }
        return ret;
      } else {
        return false;
      }

    }

    @Override
    public int hashCode() {
      int hashCode = 0;
      if (host != null) {
        hashCode += host.hashCode();
      }
      hashCode += port;
      if (user != null) {
        hashCode += user.hashCode();
      }
      return hashCode;
    }

  }
}
