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 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
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 *     http://www.apache.org/licenses/LICENSE-2.0
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package org.apache.cassandra.db.view;

import java.net.InetAddress;
import java.util.ArrayList;
import java.util.List;
import java.util.Optional;

import org.apache.cassandra.config.DatabaseDescriptor;
import org.apache.cassandra.db.Keyspace;
import org.apache.cassandra.dht.Token;
import org.apache.cassandra.locator.AbstractReplicationStrategy;
import org.apache.cassandra.locator.NetworkTopologyStrategy;
import org.apache.cassandra.utils.FBUtilities;

public final class ViewUtils
{
    private ViewUtils()
    {
    }

    
Calculate the natural endpoint for the view. The view natural endpoint is the endpoint which has the same cardinality as this node in the replication factor. The cardinality is the number at which this node would store a piece of data, given the change in replication factor. If the keyspace's replication strategy is a NetworkTopologyStrategy, we filter the ring to contain only nodes in the local datacenter when calculating cardinality. For example, if we have the following ring: A, T1 -> B, T2 -> C, T3 -> A For the token T1, at RF=1, A would be included, so A's cardinality for T1 is 1. For the token T1, at RF=2, B would be included, so B's cardinality for token T1 is 2. For token T3, at RF = 2, A would be included, so A's cardinality for T3 is 2. For a view whose base token is T1 and whose view token is T3, the pairings between the nodes would be: A writes to C (A's cardinality is 1 for T1, and C's cardinality is 1 for T3) B writes to A (B's cardinality is 2 for T1, and A's cardinality is 2 for T3) C writes to B (C's cardinality is 3 for T1, and B's cardinality is 3 for T3) 
Returns:
Optional.empty() if this method is called using a base token which does not belong to this replica/**
     * Calculate the natural endpoint for the view.
     *
     * The view natural endpoint is the endpoint which has the same cardinality as this node in the replication factor.
     * The cardinality is the number at which this node would store a piece of data, given the change in replication
     * factor. If the keyspace's replication strategy is a NetworkTopologyStrategy, we filter the ring to contain only
     * nodes in the local datacenter when calculating cardinality.
     *
     * For example, if we have the following ring:
     *   {@code A, T1 -> B, T2 -> C, T3 -> A}
     *
     * For the token T1, at RF=1, A would be included, so A's cardinality for T1 is 1. For the token T1, at RF=2, B would
     * be included, so B's cardinality for token T1 is 2. For token T3, at RF = 2, A would be included, so A's cardinality
     * for T3 is 2.
     *
     * For a view whose base token is T1 and whose view token is T3, the pairings between the nodes would be:
     *  A writes to C (A's cardinality is 1 for T1, and C's cardinality is 1 for T3)
     *  B writes to A (B's cardinality is 2 for T1, and A's cardinality is 2 for T3)
     *  C writes to B (C's cardinality is 3 for T1, and B's cardinality is 3 for T3)
     *
     * @return Optional.empty() if this method is called using a base token which does not belong to this replica
     */
    public static Optional<InetAddress> getViewNaturalEndpoint(String keyspaceName, Token baseToken, Token viewToken)
    {
        AbstractReplicationStrategy replicationStrategy = Keyspace.open(keyspaceName).getReplicationStrategy();

        String localDataCenter = DatabaseDescriptor.getEndpointSnitch().getDatacenter(FBUtilities.getBroadcastAddress());
        List<InetAddress> baseEndpoints = new ArrayList<>();
        List<InetAddress> viewEndpoints = new ArrayList<>();
        for (InetAddress baseEndpoint : replicationStrategy.getNaturalEndpoints(baseToken))
        {
            // An endpoint is local if we're not using Net
            if (!(replicationStrategy instanceof NetworkTopologyStrategy) ||
                DatabaseDescriptor.getEndpointSnitch().getDatacenter(baseEndpoint).equals(localDataCenter))
                baseEndpoints.add(baseEndpoint);
        }

        for (InetAddress viewEndpoint : replicationStrategy.getNaturalEndpoints(viewToken))
        {
            // If we are a base endpoint which is also a view replica, we use ourselves as our view replica
            if (viewEndpoint.equals(FBUtilities.getBroadcastAddress()))
                return Optional.of(viewEndpoint);

            // We have to remove any endpoint which is shared between the base and the view, as it will select itself
            // and throw off the counts otherwise.
            if (baseEndpoints.contains(viewEndpoint))
                baseEndpoints.remove(viewEndpoint);
            else if (!(replicationStrategy instanceof NetworkTopologyStrategy) ||
                     DatabaseDescriptor.getEndpointSnitch().getDatacenter(viewEndpoint).equals(localDataCenter))
                viewEndpoints.add(viewEndpoint);
        }

        // The replication strategy will be the same for the base and the view, as they must belong to the same keyspace.
        // Since the same replication strategy is used, the same placement should be used and we should get the same
        // number of replicas for all of the tokens in the ring.
        assert baseEndpoints.size() == viewEndpoints.size() : "Replication strategy should have the same number of endpoints for the base and the view";
        int baseIdx = baseEndpoints.indexOf(FBUtilities.getBroadcastAddress());

        if (baseIdx < 0)
            //This node is not a base replica of this key, so we return empty
            return Optional.empty();

        return Optional.of(viewEndpoints.get(baseIdx));
    }
}