/*
    * 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.netty5.channel.unix;
  
  import io.netty5.buffer.api.Buffer;
  import io.netty5.buffer.api.ReadableComponent;
  import io.netty5.buffer.api.ReadableComponentProcessor;
  import io.netty5.buffer.api.WritableComponent;
  import io.netty5.buffer.api.WritableComponentProcessor;
  import io.netty5.channel.ChannelOutboundBuffer.MessageProcessor;
  import io.netty5.util.internal.PlatformDependent;
  
  import java.nio.ByteBuffer;
  import java.nio.ByteOrder;
  
  import static io.netty5.channel.unix.Buffer.addressSize;
  import static io.netty5.channel.unix.Buffer.allocateDirectWithNativeOrder;
  import static io.netty5.channel.unix.Buffer.free;
  import static io.netty5.channel.unix.Buffer.nativeAddressOf;
  import static io.netty5.channel.unix.Limits.IOV_MAX;
  import static io.netty5.channel.unix.Limits.SSIZE_MAX;
  import static io.netty5.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, ReadableComponentProcessor<RuntimeException>,
                                         WritableComponentProcessor<RuntimeException> {
  
      /** The size of an address which should be 8 for 64 bits and 4 for 32 bits. */
      private static final int ADDRESS_SIZE = 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 ByteBuffer memory;
      private int count;
      private long size;
      private long maxBytes = SSIZE_MAX;
  
      public IovArray() {
          this(allocateDirectWithNativeOrder(MAX_CAPACITY));
      }
  
      public IovArray(ByteBuffer memory) {
          assert memory.position() == 0;
          if (!memory.isDirect()) {
              memory = ByteBuffer.allocateDirect(memory.capacity());
          }
          if (memory.order() != ByteOrder.nativeOrder()) {
              memory = memory.order(ByteOrder.nativeOrder());
          }
          this.memory = memory;
          memoryAddress = nativeAddressOf(memory);
      }
  
      public void clear() {
          count = 0;
          size = 0;
      }
  
     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.putLong(baseOffset, addr);
                 memory.putLong(lengthOffset, len);
             }
         } else {
             assert ADDRESS_SIZE == 4;
             if (PlatformDependent.hasUnsafe()) {
                 PlatformDependent.putInt(baseOffset + memoryAddress, (int) addr);
                 PlatformDependent.putInt(lengthOffset + memoryAddress, len);
             } else {
                 memory.putInt(baseOffset, (int) addr);
                 memory.putInt(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(long, long, int)} or
      * {@link #processMessage(Object)}.
      * <p>
      * This will not impact the existing state of the {@link IovArray}, and only applies to subsequent calls to
      * {@link #add(long, long, int)} or {@link #processMessage(Object)}.
      * <p>
      * In order to ensure some progress is made at least one {@link Buffer} 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 index}.
      */
     public long memoryAddress(int index) {
         return memoryAddress + idx(index);
     }
 
     /**
      * Release the {@link IovArray}. Once release further using of it may crash the JVM!
      */
     public void release() {
         free(memory);
     }
 
     @Override
     public boolean processMessage(Object msg) {
         if (msg instanceof io.netty5.buffer.api.Buffer) {
             var buffer = (io.netty5.buffer.api.Buffer) msg;
             if (buffer.readableBytes() == 0) {
                 return true;
             }
             return buffer.forEachReadable(0, this) >= 0;
         }
         return false;
     }
 
     private static int idx(int index) {
         return IOV_SIZE * index;
     }
 
     @Override
     public boolean process(int index, ReadableComponent component) {
         return process(component, component.readableBytes());
     }
 
     public boolean process(ReadableComponent component, int byteCount) {
         if (count == IOV_MAX) {
             // No more room!
             return false;
         }
         long nativeAddress = component.readableNativeAddress();
         assert nativeAddress != 0;
         return add(memoryAddress, nativeAddress, byteCount);
     }
 
     @Override
     public boolean process(int index, WritableComponent component) {
         return process(component, component.writableBytes());
     }
 
     public boolean process(WritableComponent component, int byteCount) {
         if (count == IOV_MAX) {
             // No more room!
             return false;
         }
         long nativeAddress = component.writableNativeAddress();
         assert nativeAddress != 0;
         return add(memoryAddress, nativeAddress, byteCount);
     }
 }