/*
    * Copyright 2016 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.kqueue;
  
  import io.netty.channel.unix.Buffer;
  import io.netty.util.internal.PlatformDependent;
  
  import java.nio.ByteBuffer;
  
  /**
   * Represents an array of kevent structures, backed by offheap memory.
   *
   * struct kevent {
   *  uintptr_t ident;
   *  short     keventFilter;
   *  u_short   flags;
   *  u_int     fflags;
   *  intptr_t  data;
   *  void      *udata;
   * };
   */
  final class KQueueEventArray {
      private static final int KQUEUE_EVENT_SIZE = Native.sizeofKEvent();
      private static final int KQUEUE_IDENT_OFFSET = Native.offsetofKEventIdent();
      private static final int KQUEUE_FILTER_OFFSET = Native.offsetofKEventFilter();
      private static final int KQUEUE_FFLAGS_OFFSET = Native.offsetofKEventFFlags();
      private static final int KQUEUE_FLAGS_OFFSET = Native.offsetofKEventFlags();
      private static final int KQUEUE_DATA_OFFSET = Native.offsetofKeventData();
  
      private ByteBuffer memory;
      private long memoryAddress;
      private int size;
      private int capacity;
  
      KQueueEventArray(int capacity) {
          if (capacity < 1) {
              throw new IllegalArgumentException("capacity must be >= 1 but was " + capacity);
          }
          memory = Buffer.allocateDirectWithNativeOrder(calculateBufferCapacity(capacity));
          memoryAddress = Buffer.memoryAddress(memory);
          this.capacity = capacity;
      }
  
      /**
       * Return the {@code memoryAddress} which points to the start of this {@link KQueueEventArray}.
       */
      long memoryAddress() {
          return memoryAddress;
      }
  
      /**
       * Return the capacity of the {@link KQueueEventArray} which represent the maximum number of {@code kevent}s
       * that can be stored in it.
       */
      int capacity() {
          return capacity;
      }
  
      int size() {
          return size;
      }
  
      void clear() {
          size = 0;
      }
  
      void evSet(int ident, short filter, short flags, int fflags) {
          reallocIfNeeded();
          evSet(getKEventOffset(size++) + memoryAddress, ident, filter, flags, fflags);
      }
  
      private void reallocIfNeeded() {
          if (size == capacity) {
              realloc(true);
          }
      }
  
      /**
       * Increase the storage of this {@link KQueueEventArray}.
       */
      void realloc(boolean throwIfFail) {
          // Double the capacity while it is "sufficiently small", and otherwise increase by 50%.
          int newLength = capacity <= 65536 ? capacity << 1 : capacity + capacity >> 1;
  
          try {
              ByteBuffer buffer = Buffer.allocateDirectWithNativeOrder(calculateBufferCapacity(newLength));
             // Copy over the old content of the memory and reset the position as we always act on the buffer as if
             // the position was never increased.
             memory.position(0).limit(size);
             buffer.put(memory);
             buffer.position(0);
 
             Buffer.free(memory);
             memory = buffer;
             memoryAddress = Buffer.memoryAddress(buffer);
         } catch (OutOfMemoryError e) {
             if (throwIfFail) {
                 OutOfMemoryError error = new OutOfMemoryError(
                         "unable to allocate " + newLength + " new bytes! Existing capacity is: " + capacity);
                 error.initCause(e);
                 throw error;
             }
         }
     }
 
     /**
      * Free this {@link KQueueEventArray}. Any usage after calling this method may segfault the JVM!
      */
     void free() {
         Buffer.free(memory);
         memoryAddress = size = capacity = 0;
     }
 
     private static int getKEventOffset(int index) {
         return index * KQUEUE_EVENT_SIZE;
     }
 
     private long getKEventOffsetAddress(int index) {
         return getKEventOffset(index) + memoryAddress;
     }
 
     private short getShort(int index, int offset) {
         if (PlatformDependent.hasUnsafe()) {
             return PlatformDependent.getShort(getKEventOffsetAddress(index) + offset);
         }
         return memory.getShort(getKEventOffset(index) + offset);
     }
 
     short flags(int index) {
         return getShort(index, KQUEUE_FLAGS_OFFSET);
     }
 
     short filter(int index) {
         return getShort(index, KQUEUE_FILTER_OFFSET);
     }
 
     short fflags(int index) {
         return getShort(index, KQUEUE_FFLAGS_OFFSET);
     }
 
     int ident(int index) {
         if (PlatformDependent.hasUnsafe()) {
             return PlatformDependent.getInt(getKEventOffsetAddress(index) + KQUEUE_IDENT_OFFSET);
         }
         return memory.getInt(getKEventOffset(index) + KQUEUE_IDENT_OFFSET);
     }
 
     long data(int index) {
         if (PlatformDependent.hasUnsafe()) {
             return PlatformDependent.getLong(getKEventOffsetAddress(index) + KQUEUE_DATA_OFFSET);
         }
         return memory.getLong(getKEventOffset(index) + KQUEUE_DATA_OFFSET);
     }
 
     private static int calculateBufferCapacity(int capacity) {
         return capacity * KQUEUE_EVENT_SIZE;
     }
 
     private static native void evSet(long keventAddress, int ident, short filter, short flags, int fflags);
 }