/*
    * 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.AllocatorControl;
  import io.netty5.buffer.api.Buffer;
  import io.netty5.buffer.api.BufferAllocator;
  import io.netty5.buffer.api.Drop;
  import io.netty5.buffer.api.MemoryManager;
  
  import java.lang.ref.Cleaner;
  import java.util.concurrent.atomic.AtomicReference;
  
  /**
   * A drop implementation that delegates to another drop instance, either when called directly, or when it becomes
   * cleanable. This ensures that objects are dropped even if they leak.
   */
  public final class CleanerDrop<T extends Buffer> implements Drop<T> {
      private Cleaner.Cleanable cleanable;
      private GatedRunner<T> runner;
  
      /**
       * Wrap the given drop instance, and produce a new drop instance that will also call the delegate drop instance if
       * it becomes cleanable.
       */
      public static <T extends Buffer> Drop<T> wrap(Drop<T> drop, MemoryManager manager) {
          return innerWrap(drop, manager);
      }
  
      private static <T extends Buffer> CleanerDrop<T> innerWrap(Drop<T> drop, MemoryManager manager) {
          CleanerDrop<T> cleanerDrop = new CleanerDrop<>();
          GatedRunner<T> runner = new GatedRunner<>(drop, manager);
          cleanerDrop.cleanable = Statics.CLEANER.register(cleanerDrop, runner);
          cleanerDrop.runner = runner;
          return cleanerDrop;
      }
  
      private CleanerDrop() {
      }
  
      @Override
      public void attach(T obj) {
          runner.prepareRecover(obj);
          runner.drop.attach(obj);
      }
  
      @Override
      public void drop(T obj) {
          runner.dropping = true;
          runner.set(obj);
          cleanable.clean();
      }
  
      @Override
      public Drop<T> fork() {
          CleanerDrop<T> drop = innerWrap(runner.drop.fork(), runner.manager);
          drop.runner.tracerFromSplitParent = true;
          drop.runner.tracer = runner.tracer;
          return drop;
      }
  
      @Override
      public String toString() {
          return "CleanerDrop(" + runner.drop + ')';
      }
  
      private static final class GatedRunner<T extends Buffer> extends AtomicReference<Object> implements Runnable {
          private static final NoOpAllocatorControl ALLOC_CONTROL = new NoOpAllocatorControl();
          private static final long serialVersionUID = 2685535951915798850L;
          final Drop<T> drop;
          final MemoryManager manager;
          volatile boolean dropping;
          volatile boolean tracerFromSplitParent;
          LifecycleTracer tracer;
  
          private GatedRunner(Drop<T> drop, MemoryManager manager) {
              this.drop = drop;
              this.manager = manager;
          }
  
          @SuppressWarnings("unchecked")
          @Override
          public void run() {
              Object obj = getAndSet(null); // Make absolutely sure we only delegate once.
              if (obj != null) {
                  if (dropping) {
                     drop.drop((T) obj);
                 } else {
                     try (Buffer recoveredBuffer = manager.recoverMemory(ALLOC_CONTROL, obj, (Drop<Buffer>) drop)) {
                         LeakDetection.reportLeak(tracer, "buffer (" + recoveredBuffer.capacity() + " bytes)");
                     }
                 }
             }
         }
 
         public void prepareRecover(T obj) {
             LifecycleTracer recoveredTracer = ResourceSupport.getTracer((ResourceSupport<?, ?>) obj);
             if (tracerFromSplitParent) {
                 tracerFromSplitParent = false;
                 tracer.splitTo(recoveredTracer);
             }
             tracer = recoveredTracer;
             set(manager.unwrapRecoverableMemory(obj));
         }
     }
 
     private static final class NoOpAllocatorControl implements AllocatorControl {
         @Override
         public BufferAllocator getAllocator() {
             throw new UnsupportedOperationException();
         }
     }
 }