/*
 * Copyright 2014-2017 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.integration.selector;

import org.springframework.integration.core.MessageSelector;
import org.springframework.integration.handler.MessageProcessor;
import org.springframework.integration.metadata.ConcurrentMetadataStore;
import org.springframework.integration.metadata.SimpleMetadataStore;
import org.springframework.messaging.Message;
import org.springframework.util.Assert;

/**
 * The {@link MessageSelector} implementation using a {@link ConcurrentMetadataStore}
 * and {@link MessageProcessor}.
 * <p>
 * The {@link #accept} method extracts {@code metadataKey} from the provided {@code message}
 * using {@link MessageProcessor} and uses the {@code timestamp} header as the {@code value}
 * (hex) by default. The {@link #valueStrategy} can be provided to override the default behaviour.
 * <p>
 * The successful result of the {@link #accept} method is based on the
 * {@link ConcurrentMetadataStore#putIfAbsent} return value. {@code true} is returned
 * if {@code putIfAbsent} returns {@code null}.
 * And, at the same time, it means that the value has been placed in the {@code MetadataStore}.
 * Otherwise the messages isn't accepted because there is already a value in the
 * {@code MetadataStore} associated with the {@code key}.
 * <p>
 * This {@link MessageSelector} is useful for an
 * <a href="http://www.eaipatterns.com/IdempotentReceiver.html">Idempotent Receiver</a>
 * implementation.
 * <p>
 * It can be used in a {@link org.springframework.integration.filter.MessageFilter}
 * or {@link org.springframework.integration.handler.advice.IdempotentReceiverInterceptor}.
 *
 * @author Artem Bilan
 * @since 4.1
 */
public class MetadataStoreSelector implements MessageSelector {

	private final ConcurrentMetadataStore metadataStore;

	private final MessageProcessor<String> keyStrategy;

	private final MessageProcessor<String> valueStrategy;

	public MetadataStoreSelector(MessageProcessor<String> keyStrategy) {
		this(keyStrategy, (MessageProcessor<String>) null);
	}

	public MetadataStoreSelector(MessageProcessor<String> keyStrategy, MessageProcessor<String> valueStrategy) {
		this(keyStrategy, valueStrategy, new SimpleMetadataStore());
	}

	public MetadataStoreSelector(MessageProcessor<String> keyStrategy, ConcurrentMetadataStore metadataStore) {
		this(keyStrategy, null, metadataStore);
	}

	public MetadataStoreSelector(MessageProcessor<String> keyStrategy, MessageProcessor<String> valueStrategy,
			ConcurrentMetadataStore metadataStore) {
		Assert.notNull(keyStrategy, "'keyStrategy' must not be null");
		Assert.notNull(metadataStore, "'metadataStore' must not be null");
		this.metadataStore = metadataStore;
		this.keyStrategy = keyStrategy;
		this.valueStrategy = valueStrategy;
	}


	@Override
	public boolean accept(Message<?> message) {
		String key = this.keyStrategy.processMessage(message);
		String value = (this.valueStrategy != null)
				? this.valueStrategy.processMessage(message)
				: Long.toString(message.getHeaders().getTimestamp());

		return this.metadataStore.putIfAbsent(key, value) == null;
	}

}