/*
    * 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.FileDescriptor;
  import java.io.IOException;
  import java.net.SocketAddress;
  import java.net.SocketException;
  import java.nio.ByteBuffer;
  import java.util.concurrent.atomic.AtomicBoolean;
  
  /**
   * The core functionality of file descriptor based I/O.
   *
   * @author Christian Kohlschütter
   */
  class AFCore extends CleanableState {
    private static final ThreadLocal<ByteBuffer> TL_BUFFER = new ThreadLocal<>();
  
    private static final String PROP_TL_BUFFER_MAX_CAPACITY =
        "org.newsclub.net.unix.thread-local-buffer.max-capacity"; // 0 means "no limit" (discouraged)
  
    private static final int TL_BUFFER_MIN_CAPACITY = 8192; // 8 kb per thread
    private static final int TL_BUFFER_MAX_CAPACITY = Integer.parseInt(System.getProperty(
        PROP_TL_BUFFER_MAX_CAPACITY, Integer.toString(1 * 1024 * 1024))); // 1 MB per thread
  
    private final AtomicBoolean closed = new AtomicBoolean(false);
  
    final FileDescriptor fd;
    final AncillaryDataSupport ancillaryDataSupport;
  
    private final boolean datagramMode;
  
    private boolean blocking = true;
    private boolean cleanFd = true;
  
    AFCore(Object observed, FileDescriptor fd, AncillaryDataSupport ancillaryDataSupport,
        boolean datagramMode) {
      super(observed);
      this.datagramMode = datagramMode;
      this.ancillaryDataSupport = ancillaryDataSupport;
  
      this.fd = fd == null ? new FileDescriptor() : fd;
    }
  
    AFCore(Object observed, FileDescriptor fd) {
      this(observed, fd, null, false);
    }
  
    @Override
    protected final void doClean() {
      if (fd != null && fd.valid() && cleanFd) {
        try {
          doClose();
        } catch (IOException e) {
          // ignore
        }
      }
      if (ancillaryDataSupport != null) {
        ancillaryDataSupport.close();
      }
    }
  
    void disableCleanFd() {
      this.cleanFd = false;
    }
  
    boolean isClosed() {
      return closed.get();
    }
  
    void doClose() throws IOException {
      if (closed.compareAndSet(false, true)) {
        NativeUnixSocket.close(fd);
      }
    }
  
    FileDescriptor validFdOrException() throws SocketException {
      FileDescriptor fdesc = validFd();
      if (fdesc == null) {
        closed.set(true);
        throw new SocketClosedException("Not open");
      }
      return fdesc;
   }
 
   synchronized FileDescriptor validFd() {
     if (isClosed()) {
       return null;
     }
     FileDescriptor descriptor = this.fd;
     if (descriptor != null) {
       if (descriptor.valid()) {
         return descriptor;
       }
     }
     return null;
   }
 
   int read(ByteBuffer dst) throws IOException {
     return read(dst, null, 0);
   }
 
   int read(ByteBuffer dst, ByteBuffer socketAddressBuffer, int options) throws IOException {
     int remaining = dst.remaining();
     if (remaining == 0) {
       return 0;
     }
     FileDescriptor fdesc = validFdOrException();
 
     int dstPos = dst.position();
 
     ByteBuffer buf;
     int pos;
 
     boolean direct = dst.isDirect();
     if (direct) {
       buf = dst;
       pos = dstPos;
     } else {
       buf = getThreadLocalDirectByteBuffer(remaining);
       remaining = Math.min(remaining, buf.remaining());
       pos = buf.position();
     }
 
     if (!blocking) {
       options |= NativeUnixSocket.OPT_NON_BLOCKING;
     }
 
     int count = NativeUnixSocket.receive(fdesc, buf, pos, remaining, socketAddressBuffer, options,
         ancillaryDataSupport, 0);
     if (count == -1) {
       return count;
     }
 
     if (direct) {
       if (count < 0) {
         throw new IllegalStateException();
       }
       dst.position(pos + count);
     } else {
       int oldLimit = buf.limit();
       if (count < oldLimit) {
         buf.limit(count);
       }
       try {
         while (buf.hasRemaining()) {
           dst.put(buf);
         }
       } finally {
         if (count < oldLimit) {
           buf.limit(oldLimit);
         }
       }
     }
     return count;
   }
 
   int write(ByteBuffer src) throws IOException {
     return write(src, null, 0);
   }
 
   int write(ByteBuffer src, SocketAddress target, int options) throws IOException {
     int remaining = src.remaining();
 
     if (remaining == 0) {
       return 0;
     }
 
     FileDescriptor fdesc = validFdOrException();
     final ByteBuffer addressTo;
     final int addressToLen;
     if (target == null) {
       addressTo = null;
       addressToLen = 0;
     } else {
       addressTo = AFSocketAddress.SOCKETADDRESS_BUFFER_TL.get();
       addressToLen = AFSocketAddress.unwrapAddressDirectBufferInternal(addressTo, target);
     }
 
     // accept "send buffer overflow" as packet loss
     // and don't retry (which may slow things down quite a bit)
     if (!blocking) {
       options |= NativeUnixSocket.OPT_NON_BLOCKING;
     }
 
     int pos = src.position();
     boolean isDirect = src.isDirect();
     ByteBuffer buf;
     int bufPos;
     if (isDirect) {
       buf = src;
       bufPos = pos;
     } else {
       buf = getThreadLocalDirectByteBuffer(remaining);
       remaining = Math.min(remaining, buf.remaining());
 
       bufPos = buf.position();
 
       while (src.hasRemaining() && buf.hasRemaining()) {
         buf.put(src);
       }
 
       buf.position(bufPos);
     }
     if (datagramMode) {
       options |= NativeUnixSocket.OPT_DGRAM_MODE;
     }
 
     int written = NativeUnixSocket.send(fdesc, buf, bufPos, remaining, addressTo, addressToLen,
         options, ancillaryDataSupport);
     src.position(pos + written);
 
     return written;
   }
 
   /**
    * Returns a per-thread reusable byte buffer for a given capacity.
    *
    * If a thread-local buffer currently uses a smaller capacity, the buffer is replaced by a larger
    * one. If the capacity exceeds a configurable maximum, a new direct buffer is allocated but not
    * cached (i.e., the previously cached one is kept but not immediately returned to the caller).
    *
    * @param capacity The desired capacity.
    * @return A byte buffer satisfying the requested capacity.
    */
   ByteBuffer getThreadLocalDirectByteBuffer(int capacity) {
     if (capacity > TL_BUFFER_MAX_CAPACITY && TL_BUFFER_MAX_CAPACITY > 0) {
       // Capacity exceeds configurable maximum limit;
       // allocate but do not cache direct buffer.
       // This may incur a performance penalty at the cost of correctness when using such capacities.
       return ByteBuffer.allocateDirect(capacity);
     }
     if (capacity < TL_BUFFER_MIN_CAPACITY) {
       capacity = TL_BUFFER_MIN_CAPACITY;
     }
     ByteBuffer buffer = TL_BUFFER.get();
     if (buffer == null || capacity > buffer.capacity()) {
       buffer = ByteBuffer.allocateDirect(capacity);
       TL_BUFFER.set(buffer);
     }
     buffer.clear();
     return buffer;
   }
 
   void implConfigureBlocking(boolean block) throws IOException {
     NativeUnixSocket.configureBlocking(validFdOrException(), block);
     this.blocking = block;
   }
 
   boolean isBlocking() {
     return blocking;
   }
 }