/*
 * Copyright 2017-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.concurrent.CompletableFuture;
import java.util.function.Consumer;

import com.google.common.cache.CacheBuilder;
import com.google.common.cache.CacheLoader;
import com.google.common.cache.LoadingCache;
import org.onosproject.store.service.AsyncDocumentTree;
import org.onosproject.store.service.DocumentPath;
import org.onosproject.store.service.DocumentTreeListener;
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 asynchronous document tree.
 */
public class CachingAsyncDocumentTree<V> extends DelegatingAsyncDocumentTree<V> implements AsyncDocumentTree<V> {
    private static final int DEFAULT_CACHE_SIZE = 10000;
    private final Logger log = getLogger(getClass());

    private final LoadingCache<DocumentPath, CompletableFuture<Versioned<V>>> cache;
    private final DocumentTreeListener<V> cacheUpdater;
    private final Consumer<Status> statusListener;

    /**
     * Default constructor.
     *
     * @param backingTree a distributed, strongly consistent map for backing
     */
    public CachingAsyncDocumentTree(AsyncDocumentTree<V> backingTree) {
        this(backingTree, DEFAULT_CACHE_SIZE);
    }

    /**
     * Constructor to configure cache size.
     *
     * @param backingTree a distributed, strongly consistent map for backing
     * @param cacheSize the maximum size of the cache
     */
    public CachingAsyncDocumentTree(AsyncDocumentTree<V> backingTree, int cacheSize) {
        super(backingTree);
        cache = CacheBuilder.newBuilder()
                .maximumSize(cacheSize)
                .build(CacheLoader.from(CachingAsyncDocumentTree.super::get));
        cacheUpdater = event -> {
            if (!event.newValue().isPresent()) {
                cache.invalidate(event.path());
            } else {
                cache.put(event.path(), CompletableFuture.completedFuture(event.newValue().get()));
            }
        };
        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);
        super.addStatusChangeListener(statusListener);
    }

    @Override
    public CompletableFuture<Versioned<V>> get(DocumentPath path) {
        return cache.getUnchecked(path);
    }

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

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

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

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

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

    @Override
    public CompletableFuture<Versioned<V>> removeNode(DocumentPath path) {
        return super.removeNode(path)
                .whenComplete((r, e) -> cache.invalidate(path));
    }
}