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/*
 * Copyright 2018 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
 *
 *      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.springframework.data.redis.support.atomic;

import lombok.RequiredArgsConstructor;

import java.util.Collection;
import java.util.function.Consumer;
import java.util.function.Supplier;

import org.springframework.dao.DataAccessException;
import org.springframework.data.redis.core.RedisOperations;
import org.springframework.data.redis.core.SessionCallback;
import org.springframework.util.CollectionUtils;

/**
 * Compare-and-set (CAS) operation using Redis Transactions ({@literal WATCH} and {@literal MULTI}) to atomically update
 * the value at {@code key}.
 * 
 * The CAS block registers a {@literal WATCH} on the key holding the expected value which guarantees that changes after
 * watching and comparing the key will rollback the transaction. The {@literal WATCH} is reset if the comparison fails.
 *
 * @author Mark Paluch
 * @since 2.0.8
 * @see RedisAtomicDouble
 * @see RedisAtomicInteger
 * @see RedisAtomicLong
 */
@RequiredArgsConstructor
class CompareAndSet implements SessionCallback {

	private final Supplier getter;
	private final Consumer setter;
	private final Object key;
	private final T expect;
	private final T update;

	/*
	 * (non-Javadoc)
	 * @see org.springframework.data.redis.core.SessionCallback#execute(org.springframework.data.redis.core.RedisOperations)
	 */
	@Override
	@SuppressWarnings("unchecked")
	public  Boolean execute(RedisOperations operations) throws DataAccessException {

		operations.watch((K) key);

		if (expect.equals(getter.get())) {

			operations.multi();
			setter.accept(update);

			if (updateSuccessful(operations.exec())) {
				return true;
			}
		}

		operations.unwatch();
		return false;
	}

	private static boolean updateSuccessful(Collection exec) {
		return !CollectionUtils.isEmpty(exec);
	}
}