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Qetcher Java client
There is a newer version: 2.0.42.rc
package de.mklinger.qetcher.client.impl.lookup;

import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
import java.util.Optional;
import java.util.concurrent.ThreadLocalRandom;
import java.util.concurrent.atomic.AtomicReference;
import java.util.stream.Collectors;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import de.mklinger.qetcher.client.model.v1.AvailableNode;
import de.mklinger.qetcher.client.model.v1.NodeLifecycle;

/**
 * @author Marc Klinger - mklinger[at]mklinger[dot]de
 */
public class NodesHolder {
	private static final Logger LOG = LoggerFactory.getLogger(NodesHolder.class);

	private final AtomicReference> fullyFunctionalNodes;
	private final AtomicReference> otherNodes;

	public NodesHolder() {
		this.fullyFunctionalNodes = new AtomicReference<>(Collections.emptyList());
		this.otherNodes = new AtomicReference<>(Collections.emptyList());
	}

	public void setNodes(final List availableNodes) {
		this.fullyFunctionalNodes.set(availableNodes.stream()
				.filter(this::isFullyFunctionalNode)
				.collect(Collectors.toList()));

		this.otherNodes.set(availableNodes.stream()
				.filter(this::isOtherNode)
				.collect(Collectors.toList()));
	}

	private boolean isFullyFunctionalNode(final AvailableNode node) {
		return node.getNodeLifecycle() == NodeLifecycle.FULLY_FUNCTIONAL;
	}

	private boolean isOtherNode(final AvailableNode node) {
		return !isFullyFunctionalNode(node);
	}

	public List getNodes() {
		final List currentFullyFunctionalNodes = fullyFunctionalNodes.get();
		final List currentOtherNodes = otherNodes.get();

		final List availableNodes = new ArrayList<>(currentFullyFunctionalNodes.size() + currentOtherNodes.size());
		availableNodes.addAll(currentFullyFunctionalNodes);
		availableNodes.addAll(currentOtherNodes);

		return availableNodes;
	}

	public Optional getRandomNode() {
		final List currentFullyFunctionalNodes = fullyFunctionalNodes.get();
		final List currentOtherNodes = otherNodes.get();

		Optional node = getRandomNode(currentFullyFunctionalNodes);

		if (!node.isPresent()) {
			node = getRandomNode(currentOtherNodes);
		}

		if (LOG.isDebugEnabled() && node.isPresent()) {
			LOG.debug("Choosing node {} at {} ({})",
					node.get().getNodeName(),
					node.get().getAddress().toUriString(),
					node.get().getNodeLifecycle());
		}

		return node;
	}

	private Optional getRandomNode(final List nodes) {
		if (nodes.isEmpty()) {
			return Optional.empty();
		}

		final int randomIdx = ThreadLocalRandom.current()
				.nextInt(nodes.size());

		return Optional.of(nodes.get(randomIdx));
	}
}