/*
 * 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.tensorflow.core.longrunning.task;

import java.util.ArrayList;
import java.util.List;
import java.util.Map;
import java.util.UUID;
import java.util.concurrent.Executors;
import java.util.concurrent.Future;
import org.apache.ignite.tensorflow.core.longrunning.LongRunningProcess;
import org.apache.ignite.tensorflow.core.util.CustomizableThreadFactory;

/**
 * Task that starts long running processes by their specifications.
 */
public class LongRunningProcessStartTask extends LongRunningProcessTask<List<UUID>> {
    /** */
    private static final long serialVersionUID = -3934183044853083034L;

    /** Process specifications. */
    private final List<LongRunningProcess> processes;

    /**
     * Constructs a new instance of start task.
     *
     * @param processes Process specifications.
     */
    public LongRunningProcessStartTask(List<LongRunningProcess> processes) {
        assert processes != null : "Processes should not be null";

        this.processes = processes;
    }

    /** {@inheritDoc} */
    @Override public List<UUID> call() {
        ArrayList<UUID> res = new ArrayList<>();

        try {
            for (LongRunningProcess proc : processes) {
                Future<?> fut = runTask(proc.getTask());

                UUID procId = saveProcMetadata(fut);

                res.add(procId);
            }
        }
        catch (Exception e) {
            // All-or-nothing strategy. In case of exception already started processes will be stopped.
            stopAllProcessesAndClearMetadata(res);

            throw e;
        }

        return res;
    }

    /**
     * Executes the task in a separate thread.
     *
     * @param task Task to be executed.
     * @return Future that allows to interrupt or get the status of the task.
     */
    private Future<?> runTask(Runnable task) {
        return Executors
            .newSingleThreadExecutor(new CustomizableThreadFactory("tf-long-running", true))
            .submit(task);
    }

    /**
     * Saves process metadata into the local metadata storage.
     *
     * @param fut Future that allows to interrupt or get the status of the task.
     * @return Process identifier.
     */
    private UUID saveProcMetadata(Future<?> fut) {
        Map<UUID, Future<?>> metadataStorage = getMetadataStorage();

        UUID procId = UUID.randomUUID();

        metadataStorage.put(procId, fut);

        return procId;
    }

    /**
     * Stop all processes by their identifiers and removes them from the metadata storage.
     *
     * @param procIds Process identifiers.
     */
    private void stopAllProcessesAndClearMetadata(List<UUID> procIds) {
        Map<UUID, Future<?>> metadataStorage = getMetadataStorage();

        for (UUID procId : procIds) {
            Future<?> fut = metadataStorage.remove(procId);
            fut.cancel(true);
        }
    }
}