/*
    * junixsocket
    *
    * Copyright 2009-2024 Christian Kohlschütter
    *
    * Licensed 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.newsclub.net.unix;
  
  import java.io.File;
  import java.io.FileDescriptor;
  import java.io.IOException;
  import java.io.RandomAccessFile;
  import java.nio.channels.FileChannel;
  import java.util.UUID;
  import java.util.concurrent.atomic.AtomicBoolean;
  
  /**
   * Hack to get a readable AND writable {@link FileChannel} for a {@link FileDescriptor}.
   *
   * @author Christian Kohlschütter
   */
  final class RAFChannelProvider extends RandomAccessFile implements FileDescriptorAccess {
    private final File tempPath;
    private final FileDescriptor fdObj;
    private final FileDescriptor rafFdOrig = new FileDescriptor();
    private final AtomicBoolean closed = new AtomicBoolean(false);
  
    private RAFChannelProvider(FileDescriptor fdObj) throws IOException {
      this(fdObj, File.createTempFile("jux", ".sock"));
    }
  
    private RAFChannelProvider(FileDescriptor fdObj, File tempPath) throws IOException {
      super(tempPath, "rw");
      this.tempPath = tempPath;
      if (!tempPath.delete() && tempPath.exists()) {
        if (!tempPath.delete()) {
          // we tried our best (looking at you, Windows)
        }
        tempPath = new File(tempPath.getParentFile(), "jux-" + UUID.randomUUID().toString()
            + ".sock");
        if (tempPath.exists()) {
          throw new IOException("Could not create a temporary path: " + tempPath);
        }
      }
      tempPath.deleteOnExit();
  
      NativeUnixSocket.ensureSupported();
  
      this.fdObj = fdObj;
  
      FileDescriptor rafFdObj = getFD();
      NativeUnixSocket.copyFileDescriptor(rafFdObj, rafFdOrig);
      NativeUnixSocket.copyFileDescriptor(fdObj, rafFdObj);
    }
  
    @Override
    public FileDescriptor getFileDescriptor() {
      return fdObj;
    }
  
    @Override
    public synchronized void close() throws IOException {
      if (!closed.getAndSet(true)) {
        NativeUnixSocket.copyFileDescriptor(rafFdOrig, getFD());
        if (!tempPath.delete()) {
          // we tried our best
        }
      }
    }
  
    public static FileChannel getFileChannel(FileDescriptor fd) throws IOException {
      return getFileChannel0(fd);
    }
  
    @SuppressWarnings("resource")
    private static FileChannel getFileChannel0(FileDescriptor fd) throws IOException {
      return new RAFChannelProvider(fd).getChannel();
    }
  }