/*
    * 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.maven.scm.provider.git;
  
  import java.io.IOException;
  import java.io.OutputStream;
  import java.io.Writer;
  import java.nio.file.FileSystem;
  import java.nio.file.Files;
  import java.nio.file.Path;
  import java.nio.file.attribute.PosixFilePermissions;
  import java.security.GeneralSecurityException;
  import java.security.KeyPair;
  import java.security.PublicKey;
  import java.util.ArrayList;
  import java.util.List;
  
  import org.apache.sshd.common.config.keys.KeyUtils;
  import org.apache.sshd.common.config.keys.writer.openssh.OpenSSHKeyEncryptionContext;
  import org.apache.sshd.common.config.keys.writer.openssh.OpenSSHKeyPairResourceWriter;
  import org.apache.sshd.git.GitLocationResolver;
  import org.apache.sshd.git.pack.GitPackCommandFactory;
  import org.apache.sshd.server.SshServer;
  import org.apache.sshd.server.auth.pubkey.KeySetPublickeyAuthenticator;
  import org.apache.sshd.server.auth.pubkey.PublickeyAuthenticator;
  import org.apache.sshd.server.session.ServerSession;
  import org.apache.sshd.util.test.CommonTestSupportUtils;
  import org.apache.sshd.util.test.CoreTestSupportUtils;
  import org.bouncycastle.openssl.PKCS8Generator;
  import org.bouncycastle.openssl.jcajce.JcaPEMWriter;
  import org.bouncycastle.openssl.jcajce.JcaPKCS8Generator;
  import org.bouncycastle.util.io.pem.PemObject;
  
  /**
   * Local Git SSH server for testing purposes.
   * It acts on top of an existing repository root directory.
   * It uses <a href="https://mina.apache.org/sshd-project/">Apache MINA SSHD</a> for the SSH server implementation.
   * <p>
   * The server generates a key pair during initialization and accepts connections using the private key which can be
   * extracted via {@link GitSshServer#writePrivateKeyAsPkcs8(Path, String)}.
   * Alternatively one may use a custom key pair and add the public key using {@link GitSshServer#addPublicKey(PublicKey)}.
   */
  public class GitSshServer {
  
      protected final SshServer sshServer;
      protected final KeyPair keyPair;
      protected final List<PublicKey> acceptedPublicKeys;
  
      public GitSshServer() throws GeneralSecurityException {
          sshServer = CoreTestSupportUtils.setupTestServer(getClass());
          keyPair = CommonTestSupportUtils.generateKeyPair(KeyUtils.RSA_ALGORITHM, 2048);
          acceptedPublicKeys = new ArrayList<>();
          acceptedPublicKeys.add(keyPair.getPublic());
          PublickeyAuthenticator authenticator = new KeySetPublickeyAuthenticator("onlykey", acceptedPublicKeys);
          sshServer.setPublickeyAuthenticator(authenticator);
      }
  
      /**
       * Writes a private key which is accepted by this server to the specified file in PKCS8 format.
       * If a passphrase is provided, the key will be encrypted using OpenSSH's format.
       * If no passphrase is provided, the key will be written as an unencrypted PKCS8 private key.
       * For the same server instance the private key is always the same, so it can be reused.
       *
       * @param file the file to write the private key to
       * @param passphrase the passphrase for encryption, or null for unencrypted
       * @throws GeneralSecurityException if a security error occurs
       * @throws IOException if an I/O error occurs
       */
      public void writePrivateKeyAsPkcs8(Path file, String passphrase) throws IOException, GeneralSecurityException {
          // encryption only optional
          if (passphrase != null) {
              // encryption with format outlined in https://dnaeon.github.io/openssh-private-key-binary-format/
              OpenSSHKeyPairResourceWriter writer = new OpenSSHKeyPairResourceWriter();
              OpenSSHKeyEncryptionContext context = new OpenSSHKeyEncryptionContext();
              context.setCipherType("192");
              context.setPassword(passphrase);
              try (OutputStream output = Files.newOutputStream(file)) {
                  writer.writePrivateKey(keyPair, "comment", context, output);
              }
          } else {
              // wrap unencrypted private key as regular PKCS8 private key
              PKCS8Generator pkcs8Generator = new JcaPKCS8Generator(keyPair.getPrivate(), null);
              PemObject pemObject = pkcs8Generator.generate();
 
             try (Writer writer = Files.newBufferedWriter(file);
                     JcaPEMWriter pw = new JcaPEMWriter(writer)) {
                 pw.writeObject(pemObject);
             }
         }
 
         if (file.getFileSystem().supportedFileAttributeViews().contains("posix")) {
             // must only be readable/writeable by me
             Files.setPosixFilePermissions(file, PosixFilePermissions.fromString("rwx------"));
         }
     }
 
     public void addPublicKey(PublicKey publicKey) {
         if (publicKey == null) {
             throw new IllegalArgumentException("Public key must not be null");
         }
         acceptedPublicKeys.add(publicKey);
     }
 
     public int getPort() {
         if (!sshServer.isStarted()) {
             throw new IllegalStateException("SSH server is not started");
         }
         return sshServer.getPort();
     }
 
     public void start(Path repositoryRoot) throws IOException {
         GitLocationResolver gitLocationResolver = new GitLocationResolver() {
             @Override
             public Path resolveRootDirectory(String command, String[] args, ServerSession session, FileSystem fs)
                     throws IOException {
                 return repositoryRoot;
             }
         };
         sshServer.setCommandFactory(new GitPackCommandFactory(gitLocationResolver));
         sshServer.start();
     }
 
     public void stop() throws IOException {
         sshServer.stop();
     }
 }