/*
 * Copyright 2016-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 static org.slf4j.LoggerFactory.getLogger;

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.BiFunction;
import java.util.function.Consumer;
import java.util.function.Predicate;

import com.google.common.util.concurrent.MoreExecutors;
import org.onosproject.store.service.AsyncConsistentMap;
import org.onosproject.store.service.MapEventListener;
import org.onosproject.store.service.Versioned;
import org.slf4j.Logger;

import com.google.common.cache.CacheBuilder;
import com.google.common.cache.CacheLoader;
import com.google.common.cache.LoadingCache;

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

/**
 * {@code AsyncConsistentMap} that caches entries on read.
 * <p>
 * The cache entries are automatically invalidated when updates are detected either locally or
 * remotely.
 * <p> This implementation only attempts to serve cached entries for {@link AsyncConsistentMap#get get}
 * {@link AsyncConsistentMap#getOrDefault(Object, Object) getOrDefault}, and
 * {@link AsyncConsistentMap#containsKey(Object) containsKey} calls. All other calls skip the cache
 * and directly go the backing map.
 *
 * @param <K> key type
 * @param <V> value type
 */
public class CachingAsyncConsistentMap<K, V> extends DelegatingAsyncConsistentMap<K, V> {
    private static final int DEFAULT_CACHE_SIZE = 10000;
    private final Logger log = getLogger(getClass());

    private final Map<MapEventListener<K, V>, Executor> mapEventListeners = new ConcurrentHashMap<>();
    private final LoadingCache<K, CompletableFuture<Versioned<V>>> cache;
    private final AsyncConsistentMap<K, V> backingMap;
    private final MapEventListener<K, V> cacheUpdater;
    private final Consumer<Status> statusListener;

    /**
     * Default constructor.
     *
     * @param backingMap a distributed, strongly consistent map for backing
     */
    public CachingAsyncConsistentMap(AsyncConsistentMap<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 CachingAsyncConsistentMap(AsyncConsistentMap<K, V> backingMap, int cacheSize) {
        super(backingMap);
        this.backingMap = backingMap;
        cache = CacheBuilder.newBuilder()
                            .maximumSize(cacheSize)
                            .build(CacheLoader.from(CachingAsyncConsistentMap.super::get));
        cacheUpdater = event -> {
            Versioned<V> newValue = event.newValue();
            if (newValue == null) {
                cache.invalidate(event.key());
            } else {
                cache.put(event.key(), CompletableFuture.completedFuture(newValue));
            }
            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<Void> destroy() {
        super.removeStatusChangeListener(statusListener);
        return super.destroy().thenCompose(v -> removeListener(cacheUpdater));
    }

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

    @Override
    public CompletableFuture<Versioned<V>> getOrDefault(K key, V defaultValue) {
        return cache.getUnchecked(key).thenCompose(r -> {
            if (r == null) {
                CompletableFuture<Versioned<V>> versioned = backingMap.getOrDefault(key, defaultValue);
                cache.put(key, versioned);
                return versioned;
            } else {
                return CompletableFuture.completedFuture(r);
            }
        }).whenComplete((r, e) -> {
            if (e != null) {
                cache.invalidate(key);
            }
        });
    }

    @Override
    public CompletableFuture<Versioned<V>> computeIf(K key,
            Predicate<? super V> condition,
            BiFunction<? super K, ? super V, ? extends V> remappingFunction) {
        return super.computeIf(key, condition, remappingFunction)
                .whenComplete((r, e) -> cache.invalidate(key));
    }

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

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

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

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

    @Override
    public CompletableFuture<Boolean> containsKey(K key) {
        return cache.getUnchecked(key).thenApply(Objects::nonNull)
                .whenComplete((r, e) -> {
                    if (e != null) {
                        cache.invalidate(key);
                    }
                });
    }

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

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

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

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

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

    @Override
    public CompletableFuture<Boolean> replace(K key, long oldVersion, V newValue) {
        return super.replace(key, oldVersion, newValue)
                .whenComplete((r, e) -> {
                    if (r) {
                        cache.invalidate(key);
                    }
                });
    }

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

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