package envoy.client.data;

import java.io.Serializable;
import java.util.*;
import java.util.function.Consumer;
import java.util.logging.*;

import envoy.util.EnvoyLog;

/**
 * Stores elements in a queue to process them later.
 *
 * @param <T> the type of cached elements
 * @author Kai S. K. Engelbart
 * @since Envoy Client v0.3-alpha
 */
public final class Cache<T> implements Consumer<T>, Serializable {

	private final Queue<T>			elements	= new LinkedList<>();
	private transient Consumer<T>	processor;

	private static final Logger	logger				= EnvoyLog.getLogger(Cache.class);
	private static final long	serialVersionUID	= 0L;

	/**
	 * Adds an element to the cache.
	 *
	 * @param element the element to add
	 * @since Envoy Client v0.3-alpha
	 */
	@Override
	public void accept(T element) {
		logger.log(Level.FINE, String.format("Adding element %s to cache", element));
		elements.offer(element);
	}

	@Override
	public String toString() {
		return String.format("Cache[elements=" + elements + "]");
	}

	/**
	 * Sets the processor to which cached elements are relayed.
	 *
	 * @param processor the processor to set
	 * @since Envoy Client v0.3-alpha
	 */
	public void setProcessor(Consumer<T> processor) { this.processor = processor; }

	/**
	 * Relays all cached elements to the processor.
	 *
	 * @throws IllegalStateException if the processor is not initialized
	 * @since Envoy Client v0.3-alpha
	 */
	public void relay() {
		if (processor == null)
			throw new IllegalStateException("Processor is not defined");
		elements.forEach(processor::accept);
		elements.clear();
	}

	/**
	 * Clears this cache of all stored elements.
	 *
	 * @since Envoy Client v0.2-beta
	 */
	public void clear() {
		elements.clear();
	}
}