/*
    * Copyright 2014 The Netty Project
    *
    * The Netty Project 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:
    *
    *   https://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 io.netty.channel.unix;
  
  import io.netty.buffer.ByteBuf;
  import io.netty.buffer.Unpooled;
  import io.netty.channel.ChannelOutboundBuffer.MessageProcessor;
  import io.netty.util.internal.PlatformDependent;
  
  import java.nio.ByteBuffer;
  import java.nio.ByteOrder;
  
  import static io.netty.channel.unix.Limits.IOV_MAX;
  import static io.netty.channel.unix.Limits.SSIZE_MAX;
  import static io.netty.util.internal.ObjectUtil.checkPositive;
  import static java.lang.Math.min;
  
  /**
   * Represent an array of struct array and so can be passed directly over via JNI without the need to do any more
   * array copies.
   *
   * The buffers are written out directly into direct memory to match the struct iov. See also {@code man writev}.
   *
   * <pre>
   * struct iovec {
   *   void  *iov_base;
   *   size_t iov_len;
   * };
   * </pre>
   *
   * See also
   * <a href="https://rkennke.wordpress.com/2007/07/30/efficient-jni-programming-iv-wrapping-native-data-objects/"
   * >Efficient JNI programming IV: Wrapping native data objects</a>.
   */
  public final class IovArray implements MessageProcessor {
  
      /** The size of an address which should be 8 for 64 bits and 4 for 32 bits. */
      private static final int ADDRESS_SIZE = Buffer.addressSize();
  
      /**
       * The size of an {@code iovec} struct in bytes. This is calculated as we have 2 entries each of the size of the
       * address.
       */
      public static final int IOV_SIZE = 2 * ADDRESS_SIZE;
  
      /**
       * The needed memory to hold up to {@code IOV_MAX} iov entries, where {@code IOV_MAX} signified
       * the maximum number of {@code iovec} structs that can be passed to {@code writev(...)}.
       */
      private static final int MAX_CAPACITY = IOV_MAX * IOV_SIZE;
  
      private final long memoryAddress;
      private final ByteBuf memory;
      private int count;
      private long size;
      private long maxBytes = SSIZE_MAX;
  
      public IovArray() {
          this(Unpooled.wrappedBuffer(Buffer.allocateDirectWithNativeOrder(MAX_CAPACITY)).setIndex(0, 0));
      }
  
      @SuppressWarnings("deprecation")
      public IovArray(ByteBuf memory) {
          assert memory.writerIndex() == 0;
          assert memory.readerIndex() == 0;
          this.memory = PlatformDependent.hasUnsafe() ? memory : memory.order(
                  PlatformDependent.BIG_ENDIAN_NATIVE_ORDER ? ByteOrder.BIG_ENDIAN : ByteOrder.LITTLE_ENDIAN);
          if (memory.hasMemoryAddress()) {
              memoryAddress = memory.memoryAddress();
          } else {
              // Fallback to using JNI as we were not be able to access the address otherwise.
  
              // Use internalNioBuffer to reduce object creation.
              // It is important to add the position as the returned ByteBuffer might be shared by multiple ByteBuf
              // instances and so has an address that starts before the start of the ByteBuf itself.
              ByteBuffer byteBuffer = memory.internalNioBuffer(0, memory.capacity());
              memoryAddress = Buffer.memoryAddress(byteBuffer) + byteBuffer.position();
          }
      }
  
      public void clear() {
          count = 0;
          size = 0;
      }
  
      /**
      * @deprecated Use {@link #add(ByteBuf, int, int)}
      */
     @Deprecated
     public boolean add(ByteBuf buf) {
         return add(buf, buf.readerIndex(), buf.readableBytes());
     }
 
     public boolean add(ByteBuf buf, int offset, int len) {
         if (count == IOV_MAX) {
             // No more room!
             return false;
         }
         if (buf.nioBufferCount() == 1) {
             if (len == 0) {
                 return true;
             }
             if (buf.hasMemoryAddress()) {
                 return add(memoryAddress, buf.memoryAddress() + offset, len);
             } else {
                 ByteBuffer nioBuffer = buf.internalNioBuffer(offset, len);
                 return add(memoryAddress, Buffer.memoryAddress(nioBuffer) + nioBuffer.position(), len);
             }
         } else {
             ByteBuffer[] buffers = buf.nioBuffers(offset, len);
             for (ByteBuffer nioBuffer : buffers) {
                 final int remaining = nioBuffer.remaining();
                 if (remaining != 0 &&
                         (!add(memoryAddress, Buffer.memoryAddress(nioBuffer) + nioBuffer.position(), remaining)
                                 || count == IOV_MAX)) {
                     return false;
                 }
             }
             return true;
         }
     }
 
     private boolean add(long memoryAddress, long addr, int len) {
         assert addr != 0;
 
         // If there is at least 1 entry then we enforce the maximum bytes. We want to accept at least one entry so we
         // will attempt to write some data and make progress.
         if ((maxBytes - len < size && count > 0) ||
                 // Check if we have enough space left
                 memory.capacity() < (count + 1) * IOV_SIZE) {
             // If the size + len will overflow SSIZE_MAX we stop populate the IovArray. This is done as linux
             //  not allow to write more bytes then SSIZE_MAX with one writev(...) call and so will
             // return 'EINVAL', which will raise an IOException.
             //
             // See also:
             // - https://linux.die.net//man/2/writev
             return false;
         }
         final int baseOffset = idx(count);
         final int lengthOffset = baseOffset + ADDRESS_SIZE;
 
         size += len;
         ++count;
 
         if (ADDRESS_SIZE == 8) {
             // 64bit
             if (PlatformDependent.hasUnsafe()) {
                 PlatformDependent.putLong(baseOffset + memoryAddress, addr);
                 PlatformDependent.putLong(lengthOffset + memoryAddress, len);
             } else {
                 memory.setLong(baseOffset, addr);
                 memory.setLong(lengthOffset, len);
             }
         } else {
             assert ADDRESS_SIZE == 4;
             if (PlatformDependent.hasUnsafe()) {
                 PlatformDependent.putInt(baseOffset + memoryAddress, (int) addr);
                 PlatformDependent.putInt(lengthOffset + memoryAddress, len);
             } else {
                 memory.setInt(baseOffset, (int) addr);
                 memory.setInt(lengthOffset, len);
             }
         }
         return true;
     }
 
     /**
      * Returns the number if iov entries.
      */
     public int count() {
         return count;
     }
 
     /**
      * Returns the size in bytes
      */
     public long size() {
         return size;
     }
 
     /**
      * Set the maximum amount of bytes that can be added to this {@link IovArray} via {@link #add(ByteBuf, int, int)}
      * <p>
      * This will not impact the existing state of the {@link IovArray}, and only applies to subsequent calls to
      * {@link #add(ByteBuf)}.
      * <p>
      * In order to ensure some progress is made at least one {@link ByteBuf} will be accepted even if it's size exceeds
      * this value.
      * @param maxBytes the maximum amount of bytes that can be added to this {@link IovArray}.
      */
     public void maxBytes(long maxBytes) {
         this.maxBytes = min(SSIZE_MAX, checkPositive(maxBytes, "maxBytes"));
     }
 
     /**
      * Get the maximum amount of bytes that can be added to this {@link IovArray}.
      * @return the maximum amount of bytes that can be added to this {@link IovArray}.
      */
     public long maxBytes() {
         return maxBytes;
     }
 
     /**
      * Returns the {@code memoryAddress} for the given {@code offset}.
      */
     public long memoryAddress(int offset) {
         return memoryAddress + idx(offset);
     }
 
     /**
      * Release the {@link IovArray}. Once release further using of it may crash the JVM!
      */
     public void release() {
         memory.release();
     }
 
     @Override
     public boolean processMessage(Object msg) throws Exception {
         if (msg instanceof ByteBuf) {
             ByteBuf buffer = (ByteBuf) msg;
             return add(buffer, buffer.readerIndex(), buffer.readableBytes());
         }
         return false;
     }
 
     private static int idx(int index) {
         return IOV_SIZE * index;
     }
 }