/*
    * junixsocket
    *
    * Copyright 2009-2024 Christian Kohlschütter
    *
    * Licensed 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
    *
   *     http://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 org.newsclub.net.unix.pool;
  
  import java.util.Objects;
  import java.util.Queue;
  import java.util.concurrent.ConcurrentLinkedQueue;
  import java.util.concurrent.atomic.AtomicInteger;
  
  import org.eclipse.jdt.annotation.NonNull;
  import org.eclipse.jdt.annotation.Nullable;
  
  /**
   * An {@link ObjectPool} implemented using {@link ConcurrentLinkedQueue}.
   *
   * @param <O> The object type.
   * @author Christian Kohlschütter
   */
  public final class ConcurrentQueueObjectPool<O> implements ObjectPool<O> {
    private final AtomicInteger count = new AtomicInteger(0);
    private final Queue<O> queue = new ConcurrentLinkedQueue<>();
    private final ObjectSupplier<O> supplier;
    private final int maxCapacity;
    private final ObjectSanitizer<O> sanitizer;
  
    /**
     * Constructs a {@link ConcurrentQueueObjectPool} with the given capacity, supplier and sanitizer.
     *
     * @param supplier The supplier.
     * @param sanitizer The sanitizer.
     * @param maxCapacity The maximum capacity.
     */
    public ConcurrentQueueObjectPool(ObjectSupplier<@NonNull O> supplier,
        ObjectSanitizer<@NonNull O> sanitizer, final int maxCapacity) {
      if (maxCapacity < 0) {
        throw new IllegalArgumentException("maxCapacity");
      }
      this.supplier = Objects.requireNonNull(supplier);
      this.sanitizer = Objects.requireNonNull(sanitizer);
      this.maxCapacity = maxCapacity;
    }
  
    @Override
    public Lease<O> take() {
      O obj = queue.poll();
      if (obj == null) {
        obj = Objects.requireNonNull(supplier.get());
      } else {
        count.decrementAndGet();
      }
      return new LeaseImpl(obj);
    }
  
    private final class LeaseImpl implements Lease<O> {
      private @Nullable O obj;
  
      public LeaseImpl(O obj) {
        this.obj = obj;
      }
  
      @SuppressWarnings("null")
      @Override
      public O get() {
        return obj;
      }
  
      @Override
      public synchronized void close() {
        @Nullable
        O theObject = obj;
        obj = null;
        if (theObject != null) {
          if (count.get() >= maxCapacity) {
            // enough objects
          } else if (!sanitizer.sanitize(theObject)) {
            // decided not to reuse
          } else {
            if (queue.offer(theObject)) {
              count.incrementAndGet();
            }
          }
        }
      }
  
     @Override
     public void discard() {
       obj = null;
     }
   }
 }