/*
    * 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.util.internal;
  
  import io.netty5.util.Resource;
  import io.netty5.util.Send;
  
  import java.lang.invoke.VarHandle;
  import java.util.Objects;
  import java.util.function.Supplier;
  
  import static java.lang.invoke.MethodHandles.lookup;
  
  public class SendFromSupplier<T extends Resource<T>> implements Send<T> {
      private static final VarHandle GATE;
      static {
          try {
              GATE = lookup().findVarHandle(SendFromSupplier.class, "gate", boolean.class);
          } catch (Exception e) {
              throw new ExceptionInInitializerError(e);
          }
      }
  
      private final Class<T> concreteObjectType;
      private final Supplier<? extends T> supplier;
  
      @SuppressWarnings("unused") // Accessed via VarHandle GATE.
      private volatile boolean gate;
  
      public SendFromSupplier(Class<T> concreteObjectType, Supplier<? extends T> supplier) {
          this.concreteObjectType = Objects.requireNonNull(concreteObjectType, "Concrete type cannot be null.");
          this.supplier = Objects.requireNonNull(supplier, "Supplier cannot be null.");
      }
  
      @Override
      public T receive() {
          if (passGate()) {
              throw new IllegalStateException("This object has already been received.");
          }
          return supplier.get();
      }
  
      @Override
      public boolean referentIsInstanceOf(Class<?> cls) {
          return cls.isAssignableFrom(concreteObjectType);
      }
  
      @Override
      public void close() {
          if (!passGate()) {
              supplier.get().close();
          }
      }
  
      /**
       * Atomically check and pass through the gate.
       *
       * @return {@code true} if the gate has already been passed,
       * otherwise {@code false} if we got through the gate first.
       */
      private boolean passGate() {
          return (boolean) GATE.getAndSet(this, true);
      }
  }