/**
 * 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.activemq.transport.amqp.client.transport;

import javax.net.ssl.KeyManager;
import javax.net.ssl.KeyManagerFactory;
import javax.net.ssl.SSLContext;
import javax.net.ssl.SSLEngine;
import javax.net.ssl.SSLParameters;
import javax.net.ssl.TrustManager;
import javax.net.ssl.TrustManagerFactory;
import javax.net.ssl.X509ExtendedKeyManager;
import javax.net.ssl.X509TrustManager;
import java.io.File;
import java.io.FileInputStream;
import java.io.InputStream;
import java.net.URI;
import java.security.KeyStore;
import java.security.KeyStoreException;
import java.security.SecureRandom;
import java.security.cert.CertificateException;
import java.security.cert.X509Certificate;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;

import io.netty.handler.ssl.SslHandler;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

/**
 * Static class that provides various utility methods used by Transport implementations.
 */
public class NettyTransportSupport {

   private static final Logger LOG = LoggerFactory.getLogger(NettyTransportSupport.class);

   /**
    * Creates a Netty SslHandler instance for use in Transports that require
    * an SSL encoder / decoder.
    *
    * @param remote  The URI of the remote peer that the SslHandler will be used against.
    * @param options The SSL options object to build the SslHandler instance from.
    * @return a new SslHandler that is configured from the given options.
    * @throws Exception if an error occurs while creating the SslHandler instance.
    */
   public static SslHandler createSslHandler(URI remote, NettyTransportSslOptions options) throws Exception {
      return new SslHandler(createSslEngine(remote, createSslContext(options), options));
   }

   /**
    * Create a new SSLContext using the options specific in the given TransportSslOptions
    * instance.
    *
    * @param options the configured options used to create the SSLContext.
    * @return a new SSLContext instance.
    * @throws Exception if an error occurs while creating the context.
    */
   public static SSLContext createSslContext(NettyTransportSslOptions options) throws Exception {
      try {
         String contextProtocol = options.getContextProtocol();
         LOG.trace("Getting SSLContext instance using protocol: {}", contextProtocol);

         SSLContext context = SSLContext.getInstance(contextProtocol);
         KeyManager[] keyMgrs = loadKeyManagers(options);
         TrustManager[] trustManagers = loadTrustManagers(options);

         context.init(keyMgrs, trustManagers, new SecureRandom());
         return context;
      } catch (Exception e) {
         LOG.error("Failed to create SSLContext: {}", e, e);
         throw e;
      }
   }

   /**
    * Create a new SSLEngine instance in client mode from the given SSLContext and
    * TransportSslOptions instances.
    *
    * @param context the SSLContext to use when creating the engine.
    * @param options the TransportSslOptions to use to configure the new SSLEngine.
    * @return a new SSLEngine instance in client mode.
    * @throws Exception if an error occurs while creating the new SSLEngine.
    */
   public static SSLEngine createSslEngine(SSLContext context, NettyTransportSslOptions options) throws Exception {
      return createSslEngine(null, context, options);
   }

   /**
    * Create a new SSLEngine instance in client mode from the given SSLContext and
    * TransportSslOptions instances.
    *
    * @param remote  the URI of the remote peer that will be used to initialize the engine, may be null if none should.
    * @param context the SSLContext to use when creating the engine.
    * @param options the TransportSslOptions to use to configure the new SSLEngine.
    * @return a new SSLEngine instance in client mode.
    * @throws Exception if an error occurs while creating the new SSLEngine.
    */
   public static SSLEngine createSslEngine(URI remote,
                                           SSLContext context,
                                           NettyTransportSslOptions options) throws Exception {
      SSLEngine engine = null;
      if (remote == null) {
         engine = context.createSSLEngine();
      } else {
         engine = context.createSSLEngine(remote.getHost(), remote.getPort());
      }

      engine.setEnabledProtocols(buildEnabledProtocols(engine, options));
      engine.setEnabledCipherSuites(buildEnabledCipherSuites(engine, options));
      engine.setUseClientMode(true);

      if (options.isVerifyHost()) {
         SSLParameters sslParameters = engine.getSSLParameters();
         sslParameters.setEndpointIdentificationAlgorithm("HTTPS");
         engine.setSSLParameters(sslParameters);
      }

      return engine;
   }

   private static String[] buildEnabledProtocols(SSLEngine engine, NettyTransportSslOptions options) {
      List<String> enabledProtocols = new ArrayList<>();

      if (options.getEnabledProtocols() != null) {
         List<String> configuredProtocols = Arrays.asList(options.getEnabledProtocols());
         LOG.trace("Configured protocols from transport options: {}", configuredProtocols);
         enabledProtocols.addAll(configuredProtocols);
      } else {
         List<String> engineProtocols = Arrays.asList(engine.getEnabledProtocols());
         LOG.trace("Default protocols from the SSLEngine: {}", engineProtocols);
         enabledProtocols.addAll(engineProtocols);
      }

      String[] disabledProtocols = options.getDisabledProtocols();
      if (disabledProtocols != null) {
         List<String> disabled = Arrays.asList(disabledProtocols);
         LOG.trace("Disabled protocols: {}", disabled);
         enabledProtocols.removeAll(disabled);
      }

      LOG.trace("Enabled protocols: {}", enabledProtocols);

      return enabledProtocols.toArray(new String[0]);
   }

   private static String[] buildEnabledCipherSuites(SSLEngine engine, NettyTransportSslOptions options) {
      List<String> enabledCipherSuites = new ArrayList<>();

      if (options.getEnabledCipherSuites() != null) {
         List<String> configuredCipherSuites = Arrays.asList(options.getEnabledCipherSuites());
         LOG.trace("Configured cipher suites from transport options: {}", configuredCipherSuites);
         enabledCipherSuites.addAll(configuredCipherSuites);
      } else {
         List<String> engineCipherSuites = Arrays.asList(engine.getEnabledCipherSuites());
         LOG.trace("Default cipher suites from the SSLEngine: {}", engineCipherSuites);
         enabledCipherSuites.addAll(engineCipherSuites);
      }

      String[] disabledCipherSuites = options.getDisabledCipherSuites();
      if (disabledCipherSuites != null) {
         List<String> disabled = Arrays.asList(disabledCipherSuites);
         LOG.trace("Disabled cipher suites: {}", disabled);
         enabledCipherSuites.removeAll(disabled);
      }

      LOG.trace("Enabled cipher suites: {}", enabledCipherSuites);

      return enabledCipherSuites.toArray(new String[0]);
   }

   private static TrustManager[] loadTrustManagers(NettyTransportSslOptions options) throws Exception {
      if (options.isTrustAll()) {
         return new TrustManager[]{createTrustAllTrustManager()};
      }

      if (options.getTrustStoreLocation() == null) {
         return null;
      }

      TrustManagerFactory fact = TrustManagerFactory.getInstance(TrustManagerFactory.getDefaultAlgorithm());

      String storeLocation = options.getTrustStoreLocation();
      String storePassword = options.getTrustStorePassword();
      String storeType = options.getStoreType();

      LOG.trace("Attempt to load TrustStore from location {} of type {}", storeLocation, storeType);

      KeyStore trustStore = loadStore(storeLocation, storePassword, storeType);
      fact.init(trustStore);

      return fact.getTrustManagers();
   }

   private static KeyManager[] loadKeyManagers(NettyTransportSslOptions options) throws Exception {
      if (options.getKeyStoreLocation() == null) {
         return null;
      }

      KeyManagerFactory fact = KeyManagerFactory.getInstance(KeyManagerFactory.getDefaultAlgorithm());

      String storeLocation = options.getKeyStoreLocation();
      String storePassword = options.getKeyStorePassword();
      String storeType = options.getStoreType();
      String alias = options.getKeyAlias();

      LOG.trace("Attempt to load KeyStore from location {} of type {}", storeLocation, storeType);

      KeyStore keyStore = loadStore(storeLocation, storePassword, storeType);
      fact.init(keyStore, storePassword != null ? storePassword.toCharArray() : null);

      if (alias == null) {
         return fact.getKeyManagers();
      } else {
         validateAlias(keyStore, alias);
         return wrapKeyManagers(alias, fact.getKeyManagers());
      }
   }

   private static KeyManager[] wrapKeyManagers(String alias, KeyManager[] origKeyManagers) {
      KeyManager[] keyManagers = new KeyManager[origKeyManagers.length];
      for (int i = 0; i < origKeyManagers.length; i++) {
         KeyManager km = origKeyManagers[i];
         if (km instanceof X509ExtendedKeyManager) {
            km = new X509AliasKeyManager(alias, (X509ExtendedKeyManager) km);
         }

         keyManagers[i] = km;
      }

      return keyManagers;
   }

   private static void validateAlias(KeyStore store, String alias) throws IllegalArgumentException, KeyStoreException {
      if (!store.containsAlias(alias)) {
         throw new IllegalArgumentException("The alias '" + alias + "' doesn't exist in the key store");
      }

      if (!store.isKeyEntry(alias)) {
         throw new IllegalArgumentException("The alias '" + alias + "' in the keystore doesn't represent a key entry");
      }
   }

   private static KeyStore loadStore(String storePath, final String password, String storeType) throws Exception {
      KeyStore store = KeyStore.getInstance(storeType);
      try (InputStream in = new FileInputStream(new File(storePath));) {
         store.load(in, password != null ? password.toCharArray() : null);
      }

      return store;
   }

   private static TrustManager createTrustAllTrustManager() {
      return new X509TrustManager() {
         @Override
         public void checkClientTrusted(X509Certificate[] x509Certificates, String s) throws CertificateException {
         }

         @Override
         public void checkServerTrusted(X509Certificate[] x509Certificates, String s) throws CertificateException {
         }

         @Override
         public X509Certificate[] getAcceptedIssuers() {
            return new X509Certificate[0];
         }
      };
   }
}
