/*
 * 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.thrift.transport;

import java.lang.ref.WeakReference;
import java.nio.charset.StandardCharsets;
import java.util.Collections;
import java.util.HashMap;
import java.util.Map;
import java.util.WeakHashMap;

import javax.security.auth.callback.CallbackHandler;
import javax.security.sasl.Sasl;
import javax.security.sasl.SaslException;
import javax.security.sasl.SaslServer;

import org.apache.thrift.transport.sasl.NegotiationStatus;
import org.apache.thrift.transport.sasl.TSaslServerDefinition;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

/**
 * Wraps another Thrift <code>TTransport</code>, but performs SASL server
 * negotiation on the call to <code>open()</code>. This class will wrap ensuing
 * communication over it, if a SASL QOP is negotiated with the other party.
 */
public class TSaslServerTransport extends TSaslTransport {

  private static final Logger LOGGER = LoggerFactory.getLogger(TSaslServerTransport.class);

  /**
   * Mapping from SASL mechanism name -> all the parameters required to
   * instantiate a SASL server.
   */
  private Map<String, TSaslServerDefinition> serverDefinitionMap = new HashMap<String, TSaslServerDefinition>();

  /**
   * Uses the given underlying transport. Assumes that addServerDefinition is
   * called later.
   *
   * @param transport
   *          Transport underlying this one.
   */
  public TSaslServerTransport(TTransport transport) throws TTransportException {
    super(transport);
  }

  /**
   * Creates a <code>SaslServer</code> using the given SASL-specific parameters.
   * See the Java documentation for <code>Sasl.createSaslServer</code> for the
   * details of the parameters.
   *
   * @param transport
   *          The underlying Thrift transport.
   */
  public TSaslServerTransport(String mechanism, String protocol, String serverName,
      Map<String, String> props, CallbackHandler cbh, TTransport transport) throws TTransportException {
    super(transport);
    addServerDefinition(mechanism, protocol, serverName, props, cbh);
  }

  private TSaslServerTransport(Map<String, TSaslServerDefinition> serverDefinitionMap, TTransport transport) throws TTransportException {
    super(transport);
    this.serverDefinitionMap.putAll(serverDefinitionMap);
  }

  /**
   * Add a supported server definition to this transport. See the Java
   * documentation for <code>Sasl.createSaslServer</code> for the details of the
   * parameters.
   */
  public void addServerDefinition(String mechanism, String protocol, String serverName,
      Map<String, String> props, CallbackHandler cbh) {
    serverDefinitionMap.put(mechanism, new TSaslServerDefinition(mechanism, protocol, serverName,
        props, cbh));
  }

  @Override
  protected SaslRole getRole() {
    return SaslRole.SERVER;
  }

  /**
   * Performs the server side of the initial portion of the Thrift SASL protocol.
   * Receives the initial response from the client, creates a SASL server using
   * the mechanism requested by the client (if this server supports it), and
   * sends the first challenge back to the client.
   */
  @Override
  protected void handleSaslStartMessage() throws TTransportException, SaslException {
    SaslResponse message = receiveSaslMessage();

    LOGGER.debug("Received start message with status {}", message.status);
    if (message.status != NegotiationStatus.START) {
      throw sendAndThrowMessage(NegotiationStatus.ERROR, "Expecting START status, received " + message.status);
    }

    // Get the mechanism name.
    String mechanismName = new String(message.payload, StandardCharsets.UTF_8);
    TSaslServerDefinition serverDefinition = serverDefinitionMap.get(mechanismName);
    LOGGER.debug("Received mechanism name '{}'", mechanismName);

    if (serverDefinition == null) {
      throw sendAndThrowMessage(NegotiationStatus.BAD, "Unsupported mechanism type " + mechanismName);
    }
    SaslServer saslServer = Sasl.createSaslServer(serverDefinition.mechanism,
        serverDefinition.protocol, serverDefinition.serverName, serverDefinition.props,
        serverDefinition.cbh);
    setSaslServer(saslServer);
  }

  /**
   * <code>TTransportFactory</code> to create
   * <code>TSaslServerTransports</code>. Ensures that a given
   * underlying <code>TTransport</code> instance receives the same
   * <code>TSaslServerTransport</code>. This is kind of an awful hack to work
   * around the fact that Thrift is designed assuming that
   * <code>TTransport</code> instances are stateless, and thus the existing
   * <code>TServers</code> use different <code>TTransport</code> instances for
   * input and output.
   */
  public static class Factory extends TTransportFactory {

    /**
     * This is the implementation of the awful hack described above.
     * <code>WeakHashMap</code> is used to ensure that we don't leak memory.
     */
    private static Map<TTransport, WeakReference<TSaslServerTransport>> transportMap =
      Collections.synchronizedMap(new WeakHashMap<TTransport, WeakReference<TSaslServerTransport>>());

    /**
     * Mapping from SASL mechanism name -> all the parameters required to
     * instantiate a SASL server.
     */
    private Map<String, TSaslServerDefinition> serverDefinitionMap = new HashMap<String, TSaslServerDefinition>();

    /**
     * Create a new Factory. Assumes that <code>addServerDefinition</code> will
     * be called later.
     */
    public Factory() {
      super();
    }

    /**
     * Create a new <code>Factory</code>, initially with the single server
     * definition given. You may still call <code>addServerDefinition</code>
     * later. See the Java documentation for <code>Sasl.createSaslServer</code>
     * for the details of the parameters.
     */
    public Factory(String mechanism, String protocol, String serverName,
        Map<String, String> props, CallbackHandler cbh) {
      super();
      addServerDefinition(mechanism, protocol, serverName, props, cbh);
    }

    /**
     * Add a supported server definition to the transports created by this
     * factory. See the Java documentation for
     * <code>Sasl.createSaslServer</code> for the details of the parameters.
     */
    public void addServerDefinition(String mechanism, String protocol, String serverName,
        Map<String, String> props, CallbackHandler cbh) {
      serverDefinitionMap.put(mechanism, new TSaslServerDefinition(mechanism, protocol, serverName,
          props, cbh));
    }

    /**
     * Get a new <code>TSaslServerTransport</code> instance, or reuse the
     * existing one if a <code>TSaslServerTransport</code> has already been
     * created before using the given <code>TTransport</code> as an underlying
     * transport. This ensures that a given underlying transport instance
     * receives the same <code>TSaslServerTransport</code>.
     */
    @Override
    public TTransport getTransport(TTransport base) throws TTransportException {
      WeakReference<TSaslServerTransport> ret = transportMap.get(base);
      if (ret == null || ret.get() == null) {
        LOGGER.debug("transport map does not contain key", base);
        ret = new WeakReference<TSaslServerTransport>(new TSaslServerTransport(serverDefinitionMap, base));
        try {
          ret.get().open();
        } catch (TTransportException e) {
          LOGGER.debug("failed to open server transport", e);
          throw new RuntimeException(e);
        }
        transportMap.put(base, ret); // No need for putIfAbsent().
                                     // Concurrent calls to getTransport() will pass in different TTransports.
      } else {
        LOGGER.debug("transport map does contain key {}", base);
      }
      return ret.get();
    }
  }
}
