/*
    * Copyright 2021 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.buffer.api.internal;
  
  import io.netty5.buffer.api.Drop;
  
  import java.lang.invoke.MethodHandles;
  import java.lang.invoke.VarHandle;
  
  public final class ArcDrop<T> implements Drop<T> {
      private static final VarHandle COUNT;
      static {
          try {
              COUNT = MethodHandles.lookup().findVarHandle(ArcDrop.class, "count", int.class);
          } catch (Exception e) {
              throw new ExceptionInInitializerError(e);
          }
      }
  
      private final Drop<T> delegate;
      @SuppressWarnings("FieldMayBeFinal")
      private volatile int count;
  
      public ArcDrop(Drop<T> delegate) {
          this.delegate = delegate;
      }
  
      public static <X> Drop<X> wrap(Drop<X> drop) {
          if (drop.getClass() == ArcDrop.class) {
              return drop;
          }
          return new ArcDrop<>(drop);
      }
  
      public static <X> Drop<X> acquire(Drop<X> drop) {
          if (drop.getClass() == ArcDrop.class) {
              ((ArcDrop<X>) drop).increment();
              return drop;
          }
          return new ArcDrop<>(drop);
      }
  
      public ArcDrop<T> increment() {
          int c;
          do {
              c = count;
              checkValidState(c);
          } while (!COUNT.compareAndSet(this, c, c + 1));
          return this;
      }
  
      @Override
      public void drop(T obj) {
          int c;
          int n;
          do {
              c = count;
              n = c - 1;
              checkValidState(c);
          } while (!COUNT.compareAndSet(this, c, n));
          if (n == -1) {
              delegate.drop(obj);
          }
      }
  
      @Override
      public Drop<T> fork() {
          return increment();
      }
  
      @Override
      public void attach(T obj) {
          delegate.attach(obj);
      }
  
      public Drop<T> unwrap() {
          return delegate;
      }
  
      @Override
      public String toString() {
          StringBuilder builder = new StringBuilder()
                  .append("ArcDrop@")
                  .append(Integer.toHexString(System.identityHashCode(this)))
                  .append('(').append(count).append(", ");
          Drop<T> drop = this;
         while ((drop = ((ArcDrop<T>) drop).unwrap()) instanceof ArcDrop) {
             builder.append(((ArcDrop<T>) drop).count).append(", ");
         }
         return builder.append(drop).append(')').toString();
     }
 
     private static void checkValidState(int count) {
         if (count == -1) {
             throw new IllegalStateException("Underlying resources have already been freed.");
         }
     }
 }