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/*
 * Copyright 2014 Basho Technologies Inc.
 *
 * 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 com.basho.riak.client.api.cap;

import com.fasterxml.jackson.core.type.TypeReference;
import java.lang.reflect.Type;
import java.util.Map;
import java.util.concurrent.ConcurrentHashMap;

/**
 * Simple factory for ConflictResolver objects.
 * 
 * When you have multiple writers there may be multiple versions of the same
 * object stored in Riak. When fetching all of these will be returned and you
 * will need to resolve the conflict.
 * 
 * 
 * To facilitate this, you can store an instance of the {@link ConflictResolver}
 * in this factory for a class. It will then be used by the {@link com.basho.riak.client.api.commands.kv.FetchValue.Response}
 * to resolve a set a of siblings to a single object.
 * 
 *
 * @author Brian Roach 
 * @since 2.0
 */
public enum ConflictResolverFactory
{
    INSTANCE;

    private final Map> resolverInstances = new ConcurrentHashMap<>();

    /**
     * Returns the instance of the ConflictResolverFactory.
     * @return The ConflictResolverFactory
     */
    public static ConflictResolverFactory getInstance()
    {
        return INSTANCE;
    }

    public  ConflictResolver getConflictResolver(Class clazz)
    {
        if (clazz == null)
        {
            throw new IllegalArgumentException("clazz cannot be null");
        }
        return getConflictResolver(clazz, null);
    }

    public  ConflictResolver getConflictResolver(TypeReference typeReference)
    {
        if (typeReference == null)
        {
            throw new IllegalArgumentException("typeReference cannot be null");
        }
        return getConflictResolver(null, typeReference);
    }

    /**
     * Return the ConflictResolver for the given class.
     * 
     * If no ConflictResolver is registered for the provided class, an instance of the
     * {@link com.basho.riak.client.cap.DefaultResolver} is returned.
     * 
     * @param  The type being resolved
     * @param clazz the class of the type being resolved
     * @return The conflict resolver for the type.
     * @throws UnresolvedConflictException
     */
    @SuppressWarnings("unchecked")
    private  ConflictResolver getConflictResolver(Type type, TypeReference typeReference)
    {
        type = type != null ? type : typeReference.getType();

        ConflictResolver resolver = (ConflictResolver) resolverInstances.get(type);
        if (resolver == null)
        {
            // Cache this?
            resolver = (ConflictResolver) new DefaultResolver();
        }

        return resolver;
    }

    /**
     * Register a ConflictResolver.
     * 
     * The instance provided will be used to resolve siblings for the given type.
     * 
     *
     * @param  The type being resolved
     * @param clazz the class of the type being resolved
     * @param resolver an instance of a class implementing ConflictResolver.
     */
    public  void registerConflictResolver(Class clazz, ConflictResolver resolver)
    {
        resolverInstances.put(clazz, resolver);
    }

    public  void registerConflictResolver(TypeReference typeReference, ConflictResolver resolver)
    {
        resolverInstances.put(typeReference.getType(), resolver);
    }

    /**
     * Unregister a ConflictResolver.
     * @param  The type being Resolved
     * @param clazz the class of the type being resolved.
     */
    public  void unregisterConflictResolver(Class clazz)
    {
        resolverInstances.remove(clazz);
    }

    public  void unregisterConflictResolver(TypeReference typeReference)
    {
        resolverInstances.remove(typeReference.getType());
    }
}