/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You 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.apache.ignite.compute;

import java.util.Collection;
import java.util.List;
import java.util.Map;
import org.apache.ignite.IgniteException;
import org.apache.ignite.cluster.ClusterNode;
import org.apache.ignite.internal.util.typedef.F;
import org.apache.ignite.internal.util.typedef.internal.U;
import org.apache.ignite.resources.LoadBalancerResource;
import org.jetbrains.annotations.NotNull;

/**
 * This class defines simplified adapter for {@link ComputeTask}. This adapter can be used
 * when jobs can be randomly assigned to available grid nodes. This adapter is sufficient
 * in most homogeneous environments where all nodes are equally suitable for executing grid
 * job. See {@link #split(int, Object)} method for more details.
 * <p>
 * Below is a coding example of how you would use {@code ComputeTaskSplitAdapter}:
 * <pre name="code" class="java">
 * public class MyFooBarTask extends ComputeTaskSplitAdapter&lt;Object, String&gt; {
 *     &#64;Override
 *     protected Collection&lt;? extends ComputeJob&gt; split(int gridSize, Object arg) throws IgniteCheckedException {
 *         List&lt;MyFooBarJob&gt; jobs = new ArrayList&lt;MyFooBarJob&gt;(gridSize);
 *
 *         for (int i = 0; i &lt; gridSize; i++) {
 *             jobs.add(new MyFooBarJob(arg));
 *         }
 *
 *         // Node assignment via load balancer
 *         // happens automatically.
 *         return jobs;
 *     }
 *
 *     // Aggregate results into one compound result.
 *     public String reduce(List&lt;ComputeJobResult&gt; results) throws IgniteCheckedException {
 *         // For the purpose of this example we simply
 *         // concatenate string representation of every
 *         // job result
 *         StringBuilder buf = new StringBuilder();
 *
 *         for (ComputeJobResult res : results) {
 *             // Append string representation of result
 *             // returned by every job.
 *             buf.append(res.getData().string());
 *         }
 *
 *         return buf.string();
 *     }
 * }
 * </pre>
 * @param <T> Type of the task execution argument.
 * @param <R> Type of the task result returning from {@link ComputeTask#reduce(List)} method.
 */
public abstract class ComputeTaskSplitAdapter<T, R> extends ComputeTaskAdapter<T, R> {
    /** */
    private static final long serialVersionUID = 0L;

    /** Load balancer. */
    @LoadBalancerResource
    private ComputeLoadBalancer balancer;

    /**
     * This is a simplified version of {@link ComputeTask#map(List, Object)} method.
     * <p>
     * This method basically takes given argument and splits it into a collection
     * of {@link ComputeJob} using provided grid size as indication of how many node are
     * available. These jobs will be randomly mapped to available grid nodes. Note that
     * if number of jobs is greater than number of grid nodes (i.e, grid size), the grid
     * nodes will be reused and some jobs will end up on the same grid nodes.
     *
     * @param gridSize Number of available grid nodes. Note that returned number of
     *      jobs can be less, equal or greater than this grid size.
     * @param arg Task execution argument. Can be {@code null}.
     * @return Collection of grid jobs. These jobs will be randomly mapped to
     *      available grid nodes. Note that if number of jobs is greater than number of
     *      grid nodes (i.e, grid size), the grid nodes will be reused and some jobs
     *      will end up on the same grid nodes.
     * @throws IgniteException Thrown in case of any errors.
     *
     * @see ComputeTask#map(List, Object)
     */
    protected abstract Collection<? extends ComputeJob> split(int gridSize, T arg) throws IgniteException;

    /** {@inheritDoc} */
    @NotNull @Override public final Map<? extends ComputeJob, ClusterNode> map(List<ClusterNode> subgrid, T arg) {
        assert subgrid != null;
        assert !subgrid.isEmpty();

        Collection<? extends ComputeJob> jobs = split(subgrid.size(), arg);

        if (F.isEmpty(jobs))
            throw new IgniteException("Split returned no jobs.");

        Map<ComputeJob, ClusterNode> map = U.newHashMap(jobs.size());

        for (ComputeJob job : jobs) {
            ClusterNode old = map.put(job, balancer.getBalancedNode(job, null));

            if (old != null)
                throw new IgniteException("Failed to map task (same job instance is being mapped more than once) " +
                    "[job=" + job + ", task=" + this + ']');
        }

        return map;
    }
}