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/*
 * Copyright 2015 Ben Manes. All Rights Reserved.
 *
 * 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 com.github.benmanes.caffeine.cache;

import static com.github.benmanes.caffeine.cache.BoundedLocalCache.MAXIMUM_EXPIRY;
import static java.util.Objects.requireNonNull;

import java.io.Serializable;
import java.util.Map;
import java.util.concurrent.CancellationException;
import java.util.concurrent.CompletableFuture;
import java.util.concurrent.CompletionException;
import java.util.concurrent.Executor;

import org.checkerframework.checker.nullness.qual.Nullable;

/**
 * Static utility methods and classes pertaining to asynchronous operations.
 *
 * @author [email protected] (Ben Manes)
 */
@SuppressWarnings("serial")
final class Async {
  static final long ASYNC_EXPIRY = (Long.MAX_VALUE >> 1) + (Long.MAX_VALUE >> 2); // 220 years

  private Async() {}

  /** Returns if the future has successfully completed. */
  static boolean isReady(@Nullable CompletableFuture future) {
    return (future != null) && future.isDone()
        && !future.isCompletedExceptionally()
        && (future.join() != null);
  }

  /** Returns the current value or null if either not done or failed. */
  @SuppressWarnings("NullAway")
  static @Nullable  V getIfReady(@Nullable CompletableFuture future) {
    return isReady(future) ? future.join() : null;
  }

  /** Returns the value when completed successfully or null if failed. */
  static @Nullable  V getWhenSuccessful(@Nullable CompletableFuture future) {
    try {
      return (future == null) ? null : future.join();
    } catch (CancellationException | CompletionException e) {
      return null;
    }
  }

  /**
   * A removal listener that asynchronously forwards the value stored in a {@link CompletableFuture}
   * if successful to the user-supplied removal listener.
   */
  static final class AsyncRemovalListener
      implements RemovalListener>, Serializable {
    private static final long serialVersionUID = 1L;

    final RemovalListener delegate;
    final Executor executor;

    AsyncRemovalListener(RemovalListener delegate, Executor executor) {
      this.delegate = requireNonNull(delegate);
      this.executor = requireNonNull(executor);
    }

    @Override
    @SuppressWarnings("FutureReturnValueIgnored")
    public void onRemoval(@Nullable K key,
        @Nullable CompletableFuture future, RemovalCause cause) {
      if (future != null) {
        future.thenAcceptAsync(value -> {
          if (value != null) {
            delegate.onRemoval(key, value, cause);
          }
        }, executor);
      }
    }

    Object writeReplace() {
      return delegate;
    }
  }

  /**
   * An eviction listener that forwards the value stored in a {@link CompletableFuture} to the
   * user-supplied eviction listener.
   */
  static final class AsyncEvictionListener
      implements RemovalListener>, Serializable {
    private static final long serialVersionUID = 1L;

    final RemovalListener delegate;

    AsyncEvictionListener(RemovalListener delegate) {
      this.delegate = requireNonNull(delegate);
    }

    @Override
    public void onRemoval(@Nullable K key,
        @Nullable CompletableFuture future, RemovalCause cause) {
      // Must have been completed and be non-null to be eligible for eviction
      V value = Async.getIfReady(future);
      if (value != null) {
        delegate.onRemoval(key, value, cause);
      }
    }

    Object writeReplace() {
      return delegate;
    }
  }

  /**
   * A weigher for asynchronous computations. When the value is being loaded this weigher returns
   * {@code 0} to indicate that the entry should not be evicted due to a size constraint. If the
   * value is computed successfully then the entry must be reinserted so that the weight is updated
   * and the expiration timeouts reflect the value once present. This can be done safely using
   * {@link Map#replace(Object, Object, Object)}.
   */
  static final class AsyncWeigher implements Weigher>, Serializable {
    private static final long serialVersionUID = 1L;

    final Weigher delegate;

    AsyncWeigher(Weigher delegate) {
      this.delegate = requireNonNull(delegate);
    }

    @Override
    public int weigh(K key, CompletableFuture future) {
      return isReady(future) ? delegate.weigh(key, future.join()) : 0;
    }

    Object writeReplace() {
      return delegate;
    }
  }

  /**
   * An expiry for asynchronous computations. When the value is being loaded this expiry returns
   * {@code ASYNC_EXPIRY} to indicate that the entry should not be evicted due to an expiry
   * constraint. If the value is computed successfully then the entry must be reinserted so that the
   * expiration is updated and the expiration timeouts reflect the value once present. The
   * duration's maximum range is reserved to coordinate with the asynchronous life cycle.
   */
  static final class AsyncExpiry implements Expiry>, Serializable {
    private static final long serialVersionUID = 1L;

    final Expiry delegate;

    AsyncExpiry(Expiry delegate) {
      this.delegate = requireNonNull(delegate);
    }

    @Override
    public long expireAfterCreate(K key, CompletableFuture future, long currentTime) {
      if (isReady(future)) {
        long duration = delegate.expireAfterCreate(key, future.join(), currentTime);
        return Math.min(duration, MAXIMUM_EXPIRY);
      }
      return ASYNC_EXPIRY;
    }

    @Override
    public long expireAfterUpdate(K key, CompletableFuture future,
        long currentTime, long currentDuration) {
      if (isReady(future)) {
        long duration = (currentDuration > MAXIMUM_EXPIRY)
            ? delegate.expireAfterCreate(key, future.join(), currentTime)
            : delegate.expireAfterUpdate(key, future.join(), currentTime, currentDuration);
        return Math.min(duration, MAXIMUM_EXPIRY);
      }
      return ASYNC_EXPIRY;
    }

    @Override
    public long expireAfterRead(K key, CompletableFuture future,
        long currentTime, long currentDuration) {
      if (isReady(future)) {
        long duration = delegate.expireAfterRead(key, future.join(), currentTime, currentDuration);
        return Math.min(duration, MAXIMUM_EXPIRY);
      }
      return ASYNC_EXPIRY;
    }

    Object writeReplace() {
      return delegate;
    }
  }
}