/*
 * Copyright Terracotta, Inc.
 *
 * 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.ehcache.impl.internal.events;

import org.ehcache.event.EventType;
import org.ehcache.core.spi.store.events.StoreEventFilter;
import org.ehcache.core.spi.store.events.StoreEventListener;

import java.util.Iterator;
import java.util.Set;
import java.util.concurrent.BlockingQueue;
import java.util.function.Supplier;

This class is responsible for handling the event fudging that needs to happen
in AbstractOffHeapStore because eviction event is fired after create / update
events have been recorded. But in reality, eviction happened first as the memory
limit on offheap is hard.

This creates a special case where we have to rewrite events in case we get an evicted
event on the same key than the previous non eviction event. In that case we need to get rid
of that former event (in case of UPDATED) or former events (EXPIRED followed by CREATED) and
add a CREATED event after the EXPIRED one.
/**
 * This class is responsible for handling the event fudging that needs to happen
 * in AbstractOffHeapStore because eviction event is fired after create / update
 * events have been recorded. But in reality, eviction happened first as the memory
 * limit on offheap is hard.
 * <p>
 * This creates a special case where we have to rewrite events in case we get an evicted
 * event on the same key than the previous non eviction event. In that case we need to get rid
 * of that former event (in case of UPDATED) or former events (EXPIRED followed by CREATED) and
 * add a CREATED event after the EXPIRED one.
 */
class FudgingInvocationScopedEventSink<K, V> extends InvocationScopedEventSink<K, V> {

  FudgingInvocationScopedEventSink(Set<StoreEventFilter<K, V>> filters, boolean ordered,
                                   BlockingQueue<FireableStoreEventHolder<K, V>>[] orderedQueues,
                                   Set<StoreEventListener<K, V>> listeners) {
    super(filters, ordered, orderedQueues, listeners);
  }

  @Override
  public void evicted(K key, Supplier<V> value) {
    V eventFudgingValue = handleEvictionPostWriteOnSameKey(key);
    super.evicted(key, value);
    if (eventFudgingValue != null) {
      created(key, eventFudgingValue);
    }
  }

  private V handleEvictionPostWriteOnSameKey(K key) {
      Iterator<FireableStoreEventHolder<K, V>> iterator = getEvents().descendingIterator();
      while (iterator.hasNext()) {
        FireableStoreEventHolder<K, V> eventHolder = iterator.next();
        if (eventHolder.getEvent().getType() != EventType.EVICTED) {
          if (eventHolder.getEvent().getKey().equals(key)) {
            // Found the previous non eviction event
            switch (eventHolder.getEvent().getType()) {
              case UPDATED:
                eventHolder.markFailed();
                return eventHolder.getEvent().getNewValue();
              case CREATED:
                eventHolder.markFailed();
                if (iterator.hasNext()) { // Expecting previous event to be EXPIRY
                  FireableStoreEventHolder<K, V> next = iterator.next();
                  if (next.getEvent().getType() == EventType.EXPIRED && next.getEvent().getKey().equals(key)) {
                    next.markFailed();
                  }
                }
                return eventHolder.getEvent().getNewValue();
            }
          } else {
            return null;
          }
        }
      }
    return null;
  }
}