/*
 * Copyright 2002-2020 the original author or authors.
 *
 * 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
 *
 *      https://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.springframework.cache.concurrent;

import java.util.concurrent.Callable;
import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.ConcurrentMap;

import org.springframework.cache.support.AbstractValueAdaptingCache;
import org.springframework.core.serializer.support.SerializationDelegate;
import org.springframework.lang.Nullable;
import org.springframework.util.Assert;

/**
 * Simple {@link org.springframework.cache.Cache} implementation based on the
 * core JDK {@code java.util.concurrent} package.
 *
 * <p>Useful for testing or simple caching scenarios, typically in combination
 * with {@link org.springframework.cache.support.SimpleCacheManager} or
 * dynamically through {@link ConcurrentMapCacheManager}.
 *
 * <p><b>Note:</b> As {@link ConcurrentHashMap} (the default implementation used)
 * does not allow for {@code null} values to be stored, this class will replace
 * them with a predefined internal object. This behavior can be changed through the
 * {@link #ConcurrentMapCache(String, ConcurrentMap, boolean)} constructor.
 *
 * @author Costin Leau
 * @author Juergen Hoeller
 * @author Stephane Nicoll
 * @since 3.1
 * @see ConcurrentMapCacheManager
 */
public class ConcurrentMapCache extends AbstractValueAdaptingCache {

        private final String name;

        private final ConcurrentMap<Object, Object> store;

        @Nullable
        private final SerializationDelegate serialization;


        /**
         * Create a new ConcurrentMapCache with the specified name.
         * @param name the name of the cache
         */
        public ConcurrentMapCache(String name) {
                this(name, new ConcurrentHashMap<>(256), true);
        }

        /**
         * Create a new ConcurrentMapCache with the specified name.
         * @param name the name of the cache
         * @param allowNullValues whether to accept and convert {@code null}
         * values for this cache
         */
        public ConcurrentMapCache(String name, boolean allowNullValues) {
                this(name, new ConcurrentHashMap<>(256), allowNullValues);
        }

        /**
         * Create a new ConcurrentMapCache with the specified name and the
         * given internal {@link ConcurrentMap} to use.
         * @param name the name of the cache
         * @param store the ConcurrentMap to use as an internal store
         * @param allowNullValues whether to allow {@code null} values
         * (adapting them to an internal null holder value)
         */
        public ConcurrentMapCache(String name, ConcurrentMap<Object, Object> store, boolean allowNullValues) {
                this(name, store, allowNullValues, null);
        }

        /**
         * Create a new ConcurrentMapCache with the specified name and the
         * given internal {@link ConcurrentMap} to use. If the
         * {@link SerializationDelegate} is specified,
         * {@link #isStoreByValue() store-by-value} is enabled
         * @param name the name of the cache
         * @param store the ConcurrentMap to use as an internal store
         * @param allowNullValues whether to allow {@code null} values
         * (adapting them to an internal null holder value)
         * @param serialization the {@link SerializationDelegate} to use
         * to serialize cache entry or {@code null} to store the reference
         * @since 4.3
         */
        protected ConcurrentMapCache(String name, ConcurrentMap<Object, Object> store,
                        boolean allowNullValues, @Nullable SerializationDelegate serialization) {

                super(allowNullValues);
                Assert.notNull(name, "Name must not be null");
                Assert.notNull(store, "Store must not be null");
                this.name = name;
                this.store = store;
                this.serialization = serialization;
        }


        /**
         * Return whether this cache stores a copy of each entry ({@code true}) or
         * a reference ({@code false}, default). If store by value is enabled, each
         * entry in the cache must be serializable.
         * @since 4.3
         */
        public final boolean isStoreByValue() {
                return (this.serialization != null);
        }

        @Override
        public final String getName() {
                return this.name;
        }

        @Override
        public final ConcurrentMap<Object, Object> getNativeCache() {
                return this.store;
        }

        @Override
        @Nullable
        protected Object lookup(Object key) {
                return this.store.get(key);
        }

        @SuppressWarnings("unchecked")
        @Override
        @Nullable
        public <T> T get(Object key, Callable<T> valueLoader) {
                return (T) fromStoreValue(this.store.computeIfAbsent(key, k -> {
                        try {
                                return toStoreValue(valueLoader.call());
                        }
                        catch (Throwable ex) {
                                throw new ValueRetrievalException(key, valueLoader, ex);
                        }
                }));
        }

        @Override
        public void put(Object key, @Nullable Object value) {
                this.store.put(key, toStoreValue(value));
        }

        @Override
        @Nullable
        public ValueWrapper putIfAbsent(Object key, @Nullable Object value) {
                Object existing = this.store.putIfAbsent(key, toStoreValue(value));
                return toValueWrapper(existing);
        }

        @Override
        public void evict(Object key) {
                this.store.remove(key);
        }

        @Override
        public boolean evictIfPresent(Object key) {
                return (this.store.remove(key) != null);
        }

        @Override
        public void clear() {
                this.store.clear();
        }

        @Override
        public boolean invalidate() {
                boolean notEmpty = !this.store.isEmpty();
                this.store.clear();
                return notEmpty;
        }

        @Override
        protected Object toStoreValue(@Nullable Object userValue) {
                Object storeValue = super.toStoreValue(userValue);
                if (this.serialization != null) {
                        try {
                                return this.serialization.serializeToByteArray(storeValue);
                        }
                        catch (Throwable ex) {
                                throw new IllegalArgumentException("Failed to serialize cache value '" + userValue +
                                                "'. Does it implement Serializable?", ex);
                        }
                }
                else {
                        return storeValue;
                }
        }

        @Override
        protected Object fromStoreValue(@Nullable Object storeValue) {
                if (storeValue != null && this.serialization != null) {
                        try {
                                return super.fromStoreValue(this.serialization.deserializeFromByteArray((byte[]) storeValue));
                        }
                        catch (Throwable ex) {
                                throw new IllegalArgumentException("Failed to deserialize cache value '" + storeValue + "'", ex);
                        }
                }
                else {
                        return super.fromStoreValue(storeValue);
                }
        }

}