/*
 * Copyright 2018-present Open Networking Foundation
 *
 * 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.onosproject.store.primitives.impl;

import java.util.Collection;
import java.util.Map;
import java.util.Objects;
import java.util.concurrent.CompletableFuture;
import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.Executor;
import java.util.function.Consumer;
import java.util.stream.Collectors;

import com.google.common.cache.CacheBuilder;
import com.google.common.cache.CacheLoader;
import com.google.common.cache.LoadingCache;
import com.google.common.collect.ImmutableSet;
import com.google.common.util.concurrent.MoreExecutors;
import org.onosproject.store.service.AsyncConsistentMultimap;
import org.onosproject.store.service.MultimapEventListener;
import org.onosproject.store.service.Versioned;
import org.slf4j.Logger;

import static org.onosproject.store.service.DistributedPrimitive.Status.INACTIVE;
import static org.onosproject.store.service.DistributedPrimitive.Status.SUSPENDED;
import static org.slf4j.LoggerFactory.getLogger;

/**
 * Caching {@link AsyncConsistentMultimap} implementation.
 */
public class CachingAsyncConsistentMultimap<K, V> extends DelegatingAsyncConsistentMultimap<K, V> {
    private static final int DEFAULT_CACHE_SIZE = 10000;
    private final Logger log = getLogger(getClass());

    private final Map<MultimapEventListener<K, V>, Executor> mapEventListeners = new ConcurrentHashMap<>();
    private final LoadingCache<K, CompletableFuture<Versioned<Collection<? extends V>>>> cache;
    private final MultimapEventListener<K, V> cacheUpdater;
    private final Consumer<Status> statusListener;

    /**
     * Default constructor.
     *
     * @param backingMap a distributed, strongly consistent map for backing
     */
    public CachingAsyncConsistentMultimap(AsyncConsistentMultimap<K, V> backingMap) {
        this(backingMap, DEFAULT_CACHE_SIZE);
    }

    /**
     * Constructor to configure cache size.
     *
     * @param backingMap a distributed, strongly consistent map for backing
     * @param cacheSize  the maximum size of the cache
     */
    public CachingAsyncConsistentMultimap(AsyncConsistentMultimap<K, V> backingMap, int cacheSize) {
        super(backingMap);
        cache = CacheBuilder.newBuilder()
            .maximumSize(cacheSize)
            .build(CacheLoader.from(CachingAsyncConsistentMultimap.super::get));
        cacheUpdater = event -> {
            V oldValue = event.oldValue();
            V newValue = event.newValue();
            CompletableFuture<Versioned<Collection<? extends V>>> future = cache.getUnchecked(event.key());
            switch (event.type()) {
                case INSERT:
                    if (future.isDone()) {
                        Versioned<Collection<? extends V>> oldVersioned = future.join();
                        Versioned<Collection<? extends V>> newVersioned = new Versioned<>(
                            ImmutableSet.<V>builder().addAll(oldVersioned.value()).add(newValue).build(),
                            oldVersioned.version(),
                            oldVersioned.creationTime());
                        cache.put(event.key(), CompletableFuture.completedFuture(newVersioned));
                    } else {
                        cache.put(event.key(), future.thenApply(versioned -> new Versioned<>(
                            ImmutableSet.<V>builder().addAll(versioned.value()).add(newValue).build(),
                            versioned.version(),
                            versioned.creationTime())));
                    }
                    break;
                case REMOVE:
                    if (future.isDone()) {
                        Versioned<Collection<? extends V>> oldVersioned = future.join();
                        cache.put(event.key(), CompletableFuture.completedFuture(new Versioned<>(oldVersioned.value()
                            .stream()
                            .filter(value -> !Objects.equals(value, oldValue))
                            .collect(Collectors.toSet()), oldVersioned.version(), oldVersioned.creationTime())));
                    } else {
                        cache.put(event.key(), future.thenApply(versioned -> new Versioned<>(versioned.value()
                            .stream()
                            .filter(value -> !Objects.equals(value, oldValue))
                            .collect(Collectors.toSet()), versioned.version(), versioned.creationTime())));
                    }
                    break;
                default:
                    break;
            }
            mapEventListeners.forEach((listener, executor) -> executor.execute(() -> listener.event(event)));
        };
        statusListener = status -> {
            log.debug("{} status changed to {}", this.name(), status);
            // If the status of the underlying map is SUSPENDED or INACTIVE
            // we can no longer guarantee that the cache will be in sync.
            if (status == SUSPENDED || status == INACTIVE) {
                cache.invalidateAll();
            }
        };
        super.addListener(cacheUpdater, MoreExecutors.directExecutor());
        super.addStatusChangeListener(statusListener);
    }

    @Override
    public CompletableFuture<Boolean> containsKey(K key) {
        return get(key).thenApply(value -> value != null && !value.value().isEmpty());
    }

    @Override
    public CompletableFuture<Boolean> put(K key, V value) {
        return super.put(key, value)
            .whenComplete((r, e) -> cache.invalidate(key));
    }

    @Override
    public CompletableFuture<Boolean> remove(K key, V value) {
        return super.remove(key, value)
            .whenComplete((r, e) -> cache.invalidate(key));
    }

    @Override
    public CompletableFuture<Boolean> removeAll(K key, Collection<? extends V> values) {
        return super.removeAll(key, values)
            .whenComplete((r, e) -> cache.invalidate(key));
    }

    @Override
    public CompletableFuture<Versioned<Collection<? extends V>>> removeAll(K key) {
        return super.removeAll(key)
            .whenComplete((r, e) -> cache.invalidate(key));
    }

    @Override
    public CompletableFuture<Boolean> putAll(K key, Collection<? extends V> values) {
        return super.putAll(key, values)
            .whenComplete((r, e) -> cache.invalidate(key));
    }

    @Override
    public CompletableFuture<Versioned<Collection<? extends V>>> replaceValues(K key, Collection<V> values) {
        return super.replaceValues(key, values)
            .whenComplete((r, e) -> cache.invalidate(key));
    }

    @Override
    public CompletableFuture<Void> clear() {
        return super.clear()
            .whenComplete((r, e) -> cache.invalidateAll());
    }

    @Override
    public CompletableFuture<Versioned<Collection<? extends V>>> get(K key) {
        return cache.getUnchecked(key)
            .whenComplete((r, e) -> {
                if (e != null) {
                    cache.invalidate(key);
                }
            });
    }

    @Override
    public CompletableFuture<Void> addListener(MultimapEventListener<K, V> listener, Executor executor) {
        mapEventListeners.put(listener, executor);
        return CompletableFuture.completedFuture(null);
    }

    @Override
    public CompletableFuture<Void> removeListener(MultimapEventListener<K, V> listener) {
        mapEventListeners.remove(listener);
        return CompletableFuture.completedFuture(null);
    }

    @Override
    public CompletableFuture<Void> destroy() {
        super.removeStatusChangeListener(statusListener);
        return super.destroy().thenCompose(v -> removeListener(cacheUpdater));
    }
}