/*
 * Copyright 2018-present Open Networking Foundation
 *
 * 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 org.onosproject.workflow.impl;

import com.fasterxml.jackson.databind.node.JsonNodeFactory;
import org.onosproject.cluster.ClusterService;
import org.onosproject.cluster.LeadershipService;
import org.onosproject.cluster.NodeId;
import org.onosproject.core.ApplicationId;
import org.onosproject.core.CoreService;
import org.onosproject.store.service.StorageException;
import org.onosproject.workflow.api.DefaultWorkplace;
import org.onosproject.workflow.api.EventHintSupplier;
import org.onosproject.workflow.api.EventTask;
import org.onosproject.workflow.api.JsonDataModelInjector;
import org.onosproject.workflow.api.JsonDataModelTree;
import org.onosproject.workflow.api.ProgramCounter;
import org.onosproject.workflow.api.SystemWorkflowContext;
import org.onosproject.workflow.api.EventTimeoutTask;
import org.onosproject.workflow.api.TimeoutTask;
import org.onosproject.workflow.api.TimerChain;
import org.onosproject.workflow.api.TriggerWorklet;
import org.onosproject.workflow.api.WorkflowEventMetaData;
import org.onosproject.workflow.api.Worklet;
import org.onosproject.workflow.api.Workflow;
import org.onosproject.workflow.api.WorkflowContext;
import org.onosproject.workflow.api.WorkflowData;
import org.onosproject.workflow.api.ContextEventMapStore;
import org.onosproject.workflow.api.WorkflowState;
import org.onosproject.workflow.api.WorkflowStore;
import org.onosproject.workflow.api.WorkflowBatchDelegate;
import org.onosproject.workflow.api.WorkflowDataEvent;
import org.onosproject.workflow.api.WorkflowDataListener;
import org.onosproject.workflow.api.WorkflowException;
import org.onosproject.workflow.api.HandlerTask;
import org.onosproject.workflow.api.HandlerTaskBatchDelegate;
import org.onosproject.workflow.api.Workplace;
import org.onosproject.workflow.api.WorkplaceStore;
import org.onosproject.workflow.api.WorkplaceStoreDelegate;
import org.onosproject.workflow.api.WorkflowExecutionService;
import org.onosproject.workflow.api.WorkletDescription;
import org.onosproject.workflow.api.StaticDataModelInjector;
import org.onosproject.event.AbstractListenerManager;
import org.onosproject.event.Event;
import org.onosproject.net.intent.WorkPartitionService;
import org.osgi.service.component.annotations.Activate;
import org.osgi.service.component.annotations.Component;
import org.osgi.service.component.annotations.Deactivate;
import org.osgi.service.component.annotations.Reference;
import org.osgi.service.component.annotations.ReferenceCardinality;
import org.slf4j.Logger;

import java.util.Collection;
import java.util.List;
import java.util.Map;
import java.util.Objects;
import java.util.Set;
import java.util.UUID;
import java.util.concurrent.CompletableFuture;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.ScheduledExecutorService;
import java.util.stream.Collectors;

import static java.util.concurrent.Executors.newFixedThreadPool;
import static java.util.concurrent.Executors.newSingleThreadExecutor;
import static java.util.concurrent.Executors.newSingleThreadScheduledExecutor;
import static org.onlab.util.Tools.groupedThreads;
import static org.onosproject.workflow.api.WorkflowAttribute.REMOVE_AFTER_COMPLETE;
import static org.slf4j.LoggerFactory.getLogger;

@Component(immediate = true, service = WorkflowExecutionService.class)
public class WorkFlowEngine extends AbstractListenerManager<WorkflowDataEvent, WorkflowDataListener>
        implements WorkflowExecutionService {

    protected static final Logger log = getLogger(WorkFlowEngine.class);
    @Reference(cardinality = ReferenceCardinality.MANDATORY)
    protected CoreService coreService;

    @Reference(cardinality = ReferenceCardinality.MANDATORY)
    protected ClusterService clusterService;

    @Reference(cardinality = ReferenceCardinality.MANDATORY)
    protected LeadershipService leadershipService;

    @Reference(cardinality = ReferenceCardinality.MANDATORY)
    protected WorkPartitionService partitionService;

    @Reference(cardinality = ReferenceCardinality.MANDATORY)
    protected WorkplaceStore workplaceStore;

    @Reference(cardinality = ReferenceCardinality.MANDATORY)
    protected WorkflowStore workflowStore;

    @Reference(cardinality = ReferenceCardinality.MANDATORY)
    protected ContextEventMapStore eventMapStore;

    private final WorkplaceStoreDelegate workplaceStoreDelegate = this::post;

    private final WorkflowBatchDelegate workflowBatchDelegate = new InternalWorkflowBatchDelegate();
    private final WorkflowAccumulator workflowAccumulator = new WorkflowAccumulator(workflowBatchDelegate);

    private final HandlerTaskBatchDelegate eventtaskBatchDelegate = new InternalHandlerTaskBatchDelegate();
    private final HandlerTaskAccumulator eventtaskAccumulator = new HandlerTaskAccumulator(eventtaskBatchDelegate);

    private ExecutorService workflowBatchExecutor;
    private ExecutorService workflowExecutor;

    private ExecutorService handlerTaskBatchExecutor;
    private ExecutorService handlerTaskExecutor;

    private static final int DEFAULT_WORKFLOW_THREADS = 12;
    private static final int DEFAULT_EVENTTASK_THREADS = 12;
    private static final int MAX_REGISTER_EVENTMAP_WAITS = 10;

    private ScheduledExecutorService eventMapTriggerExecutor;

    private TimerChain timerChain = new TimerChain();

    private JsonDataModelInjector dataModelInjector = new JsonDataModelInjector();
    private StaticDataModelInjector staticDataModelInjector = new StaticDataModelInjector();

    public static final String APPID = "org.onosproject.workflow";
    private ApplicationId appId;
    private NodeId localNodeId;

    @Activate
    public void activate() {
        appId = coreService.registerApplication(APPID);
        workplaceStore.setDelegate(workplaceStoreDelegate);
        localNodeId = clusterService.getLocalNode().id();
        leadershipService.runForLeadership(appId.name());

        workflowBatchExecutor = newSingleThreadExecutor(
                groupedThreads("onos/workflow", "workflow-batch", log));
        workflowExecutor = newFixedThreadPool(DEFAULT_WORKFLOW_THREADS,
                groupedThreads("onos/workflow-exec", "worker-%d", log));
        handlerTaskBatchExecutor = newSingleThreadExecutor(
                groupedThreads("onos/workflow", "handlertask-batch", log));
        handlerTaskExecutor = newFixedThreadPool(DEFAULT_EVENTTASK_THREADS,
                groupedThreads("onos/handlertask-exec", "worker-%d", log));
        eventMapTriggerExecutor = newSingleThreadScheduledExecutor(
                groupedThreads("onos/workflow-engine", "eventmap-trigger-executor"));

        (new WorkplaceWorkflow(this, workflowStore)).registerWorkflows();
        JsonDataModelTree data = new JsonDataModelTree(JsonNodeFactory.instance.objectNode());
        workplaceStore.registerWorkplace(Workplace.SYSTEM_WORKPLACE,
                new DefaultWorkplace(Workplace.SYSTEM_WORKPLACE, data));

        log.info("Started");
    }

    @Deactivate
    public void deactivate() {
        leadershipService.withdraw(appId.name());
        workplaceStore.unsetDelegate(workplaceStoreDelegate);
        workflowBatchExecutor.shutdown();
        workflowExecutor.shutdown();
        handlerTaskBatchExecutor.shutdown();
        handlerTaskExecutor.shutdown();
        eventMapTriggerExecutor.shutdown();
        log.info("Stopped");
    }

    @Override
    public void execInitWorklet(WorkflowContext context) {

        Workflow workflow = workflowStore.get(context.workflowId());
        if (workflow == null) {
            log.error("Invalid workflow {}", context.workflowId());
            return;
        }

        initWorkletExecution(context);
        try {
            Worklet initWorklet = workflow.init(context);
            if (initWorklet != null) {

                log.info("{} worklet.process:{}", context.name(), initWorklet.tag());
                log.trace("{} context: {}", context.name(), context);

                dataModelInjector.inject(initWorklet, context);
                initWorklet.process(context);
                dataModelInjector.inhale(initWorklet, context);

                log.info("{} worklet.process(done): {}", context.name(), initWorklet.tag());
                log.trace("{} context: {}", context.name(), context);
            }

        } catch (WorkflowException e) {
            log.error("Exception: ", e);
            context.setCause(e.getMessage());
            context.setState(WorkflowState.EXCEPTION);
            workplaceStore.commitContext(context.name(), context, false);
            return;
        }
        // trigger the execution of next worklet.
        workplaceStore.registerContext(context.name(), context);
    }

    @Override
    public void eval(String contextName) {

        final WorkflowContext latestContext = workplaceStore.getContext(contextName);
        if (latestContext == null) {
            log.error("Invalid workflow context {}", contextName);
            return;
        }

        initWorkletExecution(latestContext);

        workplaceStore.commitContext(latestContext.name(), latestContext, true);

    }

    @Override
    public void eventMapTrigger(Event event, EventHintSupplier supplier) {

        if (event.subject() instanceof SystemWorkflowContext) {
            return;
        }

        Map<String, WorkflowEventMetaData> eventMap;

        String eventHint;
        try {
            eventHint = supplier.apply(event);
        } catch (Throwable e) {
            log.error("Exception: ", e);
            return;
        }

        if (eventHint == null) {
            // do nothing
            log.error("Invalid eventHint, event: {}", event);
            return;
        }

        try {
            eventMap = eventMapStore.getEventMapByHint(event.getClass().getName(), eventHint);
            if (Objects.isNull(eventMap) || eventMap.isEmpty()) {
                // do nothing;
                log.debug("Invalid eventMap, event: {}", event);
                return;
            }

            for (Map.Entry<String, WorkflowEventMetaData> entry : eventMap.entrySet()) {
                String contextName = entry.getKey();
                ProgramCounter pc = ProgramCounter.valueOf("INVALID_WORKLET", 0);
                WorkflowContext context = null;

                context = workplaceStore.getContext(contextName);

                if (Objects.isNull(context)) {
                    log.info("Invalid context: {}, event: {}", contextName, event);
                    continue;
                }

                EventTask eventtask = null;
                if (eventMapStore.isTriggerSet(event.getClass().getName(), eventHint, contextName)) {
                    try {
                        eventtask = EventTask.builder()
                               .event(event)
                               .eventHint(eventHint)
                               .context(context)
                               .programCounter(pc)
                               .build();
                    } catch (WorkflowException e) {
                        log.error("Exception: ", e);
                    }

                    log.debug("eventtaskAccumulator.add: task: {}", eventtask);
                    if (!Objects.isNull(eventtask)) {
                        eventtaskAccumulator.add(eventtask);
                    }
                }
                /*Both type of event is being scheduled here if applicable.
                If worfklow trigger event is set but may not be a valid one for current event type,
                then normal worklet event should be processed if applicable. But validity of workflow
                trigger event would be checked later, so as of now both kind of event would be scheduled.
                later while trigger event processing, its validity is found to be true, then worklet events
                would be unregistered and eventually these events wont be processed.*/
                if (eventMapStore.isEventMapPresent(contextName)) {
                    try {
                        pc = entry.getValue().getProgramCounter();
                    } catch (IllegalArgumentException e) {
                        log.error("Exception: ", e);
                        continue;
                    }
                    try {
                        eventtask = EventTask.builder()
                               .event(event)
                               .eventHint(eventHint)
                               .context(context)
                               .programCounter(pc)
                               .build();
                    } catch (WorkflowException e) {
                        log.error("Exception: ", e);
                    }

                    log.debug("eventtaskAccumulator.add: task: {}", eventtask);
                    if (!Objects.isNull(eventtask)) {
                        eventtaskAccumulator.add(eventtask);
                    }

                }
            }

        } catch (WorkflowException we) {
            log.error("Exception {} occured in fetching contexts for trigger event {}", we, event);
        }
    }

    @Override
    public void registerEventMap(Class<? extends Event> eventType, Set<String> eventHintSet,
                                 String contextName, ProgramCounter programCounter) throws WorkflowException {
        eventMapStore.registerEventMap(eventType.getName(), eventHintSet, contextName, programCounter);
        for (String eventHint : eventHintSet) {
            for (int i = 0; i < MAX_REGISTER_EVENTMAP_WAITS; i++) {
                Map<String, WorkflowEventMetaData> eventMap =
                        eventMapStore.getEventMapByHint(eventType.getName(), eventHint);
                if (eventMap != null && eventMap.containsKey(contextName)) {
                    break;
                }
                try {
                    log.info("sleep {}", i);
                    Thread.sleep(10L * (i + 1));
                } catch (InterruptedException e) {
                    log.error("Exception: ", e);
                    Thread.currentThread().interrupt();
                }
            }
        }

    }

    @Override
    protected void post(WorkflowDataEvent event) {

        if (event.subject() == null || !isRelevant(event.subject())) {
            log.debug("ignore event {}", event);
            return;
        }

        // trigger next worklet selection
        WorkflowData dataModelContainer = event.subject();
        switch (event.type()) {
            case INSERT:
            case UPDATE:
                if (dataModelContainer.triggerNext()) {
                    log.debug("workflowAccumulator.add: {}", dataModelContainer);
                    workflowAccumulator.add(dataModelContainer);
                } else {
                    log.debug("pass-workflowAccumulator.add: {}", dataModelContainer);
                }
                break;
            case REMOVE:
                break;
            default:
        }

        // trigger EventTask for WorkflowDataEvent
        eventMapTriggerExecutor.submit(
                () -> eventMapTrigger(
                        event,
                        // event hint supplier
                        (ev) -> {
                            if (ev == null || ev.subject() == null) {
                                return null;
                            }

                            if (ev.subject() instanceof WorkflowData) {
                                return ((WorkflowData) ev.subject()).name();
                            } else {
                                return null;
                            }
                        }
                )
        );
    }

    /**
     * Checks whether this workflow data job is relevant to this ONOS node.
     *
     * @param job workflow data
     * @return checking result
     */
    private boolean isRelevant(WorkflowData job) {
        // distributes event processing with work-partition
        return partitionService.isMine(job.distributor(), this::stringHash);
    }

    /**
     * Gets hash of the string.
     *
     * @param str string to get a hash
     * @return hash value
     */
    public Long stringHash(String str) {
        return UUID.nameUUIDFromBytes(str.getBytes()).getMostSignificantBits();
    }

    /**
     * Class for handler task batch delegation.
     */
    private class InternalHandlerTaskBatchDelegate implements HandlerTaskBatchDelegate {
        @Override
        public void execute(Collection<Collection<HandlerTask>> operations) {
            log.debug("Execute {} operation(s).", operations.size());

            CompletableFuture.runAsync(() -> {
                List<CompletableFuture<Collection<HandlerTask>>> futures = operations.stream()
                        .map(
                                x -> CompletableFuture.completedFuture(x)
                                        .thenApplyAsync(WorkFlowEngine.this::processHandlerTask, handlerTaskExecutor)
                                        .exceptionally(e -> null)
                        )
                        .collect(Collectors.toList());

                // waiting the completion of futures
                futures.parallelStream().forEach(x -> x.join());

            }, handlerTaskBatchExecutor).exceptionally(e -> {
                log.error("Error submitting batches:", e);
                return null;
            }).thenRun(eventtaskAccumulator::ready);
        }
    }

    /**
     * Initializes worklet execution.
     *
     * @param context workflow context
     */
    private void initWorkletExecution(WorkflowContext context) {
        context.setState(WorkflowState.RUNNING);
        context.setCause("");
        context.setWorkflowExecutionService(this);
        context.setWorkflowStore(workflowStore);
        context.setWorkplaceStore(workplaceStore);
        context.setEventMapStore(eventMapStore);
        context.waitCompletion(null, null, null, 0L);
        context.setTriggerNext(false);
    }

    /**
     * Processes handler tasks.
     *
     * @param tasks handler tasks
     * @return handler tasks processed
     */
    private Collection<HandlerTask> processHandlerTask(Collection<HandlerTask> tasks) {

        for (HandlerTask task : tasks) {
            if (task instanceof EventTimeoutTask) {
                execEventTimeoutTask((EventTimeoutTask) task);
            } else if (task instanceof TimeoutTask) {
                execTimeoutTask((TimeoutTask) task);
            } else if (task instanceof EventTask) {
                execEventTask((EventTask) task);
            } else {
                log.error("Unsupported handler task {}", task);
            }
        }

        return null;
    }

    /**
     * Executes event task.
     *
     * @param task event task
     * @return event task
     */
    private EventTask execEventTask(EventTask task) {

        WorkflowContext context = (WorkflowContext) (task.context());
        String cxtName = context.name();
        try {
            if (eventMapStore.isTriggerSet(task.event().getClass().getName(), task.eventHint(), cxtName)) {
                WorkflowContext workflowContext = workplaceStore.getContext(cxtName);
                Workflow workflow = workflowStore.get(workflowContext.workflowId());
                String triggerWorkletName = workflow.getTriggerWorkletClassName().get();
                Worklet worklet = workflow.getTriggerWorkletInstance(triggerWorkletName);
                if (worklet instanceof TriggerWorklet) {
                    if (((TriggerWorklet) worklet).isTriggerValid(workflowContext, task.event())) {
                        if (Objects.nonNull(workflowContext.completionEventType())) {
                            eventMapStore.unregisterEventMap(workflowContext.completionEventType().getName(),
                                                             workflowContext.name());
                        }
                        initWorkletExecution(workflowContext);
                        workflowContext.setCurrent(ProgramCounter.INIT_PC);
                        workplaceStore.commitContext(cxtName, workflowContext, true);
                    }
                }
            }

        } catch (WorkflowException we) {
            log.error("Error Occurred in validating trigger for eventType {} eventHint {} context name {}",
                      task.eventType(), task.eventHint(), cxtName);
        }

        if (!eventMapStore.isEventMapPresent(cxtName)) {
            log.trace("EventMap doesnt exist for taskcontext:{}", cxtName);
            return task;
        }

        log.debug("execEventTask- task: {}, hash: {}", task, stringHash(task.context().distributor()));

        Workflow workflow = workflowStore.get(context.workflowId());
        if (workflow == null) {
            log.error("Invalid workflow {}", context.workflowId());
            return task;
        }

        WorkflowContext latestContext = workplaceStore.getContext(context.name());
        if (latestContext == null) {
            log.error("Invalid workflow context {}", context.name());
            return task;
        }

        try {
            if (!Objects.equals(latestContext.current(), task.programCounter())) {
                log.error("Current worklet({}) is not mismatched with task work({}). Ignored.",
                        latestContext.current(), task.programCounter());
                return task;
            }

            Worklet worklet = workflow.getWorkletInstance(task.programCounter());
            if (Worklet.Common.COMPLETED.equals(worklet) || Worklet.Common.INIT.equals(worklet)) {
                log.error("Current worklet is {}, Ignored", worklet);
                return task;
            }

            initWorkletExecution(latestContext);

            log.info("{} worklet.isCompleted:{}", latestContext.name(), worklet.tag());
            log.trace("{} task:{}, context: {}", latestContext.name(), task, latestContext);

            dataModelInjector.inject(worklet, latestContext);
            boolean completed = worklet.isCompleted(latestContext, task.event());
            dataModelInjector.inhale(worklet, latestContext);

            if (completed) {

                log.info("{} worklet.isCompleted(true):{}", latestContext.name(), worklet.tag());
                log.trace("{} task:{}, context: {}", latestContext.name(), task, latestContext);

                eventMapStore.unregisterEventMap(
                        task.eventType(), latestContext.name());

                //completed case
                //increase program counter
                ProgramCounter pc = latestContext.current();
                latestContext.setCurrent(workflow.increased(pc));

                workplaceStore.commitContext(latestContext.name(), latestContext, true);
                return null;
            } else {

                log.info("{} worklet.isCompleted(false):{}", latestContext.name(), worklet.tag());
                log.trace("{} task:{}, context: {}", latestContext.name(), task, latestContext);

                workplaceStore.commitContext(latestContext.name(), latestContext, false);
            }

        } catch (WorkflowException e) {
            log.error("Exception: ", e);
            latestContext.setCause(e.getMessage());
            latestContext.setState(WorkflowState.EXCEPTION);
            workplaceStore.commitContext(latestContext.name(), latestContext, false);
        } catch (StorageException e) {
            log.error("Exception: ", e);
            // StorageException does not commit context.
        } catch (Exception e) {
            log.error("Exception: ", e);
            latestContext.setCause(e.getMessage());
            latestContext.setState(WorkflowState.EXCEPTION);
            workplaceStore.commitContext(latestContext.name(), latestContext, false);
        }

        return task;
    }

    /**
     * Executes event timeout task.
     *
     * @param task event timeout task
     * @return handler task
     */
    private HandlerTask execEventTimeoutTask(EventTimeoutTask task) {

        if (!eventMapStore.isEventMapPresent(task.context().name())) {
            log.trace("EventMap doesnt exist for taskcontext:{}", task.context().name());
            return task;
        }

        log.debug("execEventTimeoutTask- task: {}, hash: {}", task, stringHash(task.context().distributor()));

        WorkflowContext context = (WorkflowContext) (task.context());
        Workflow workflow = workflowStore.get(context.workflowId());
        if (workflow == null) {
            log.error("execEventTimeoutTask: Invalid workflow {}", context.workflowId());
            return task;
        }

        WorkflowContext latestContext = workplaceStore.getContext(context.name());
        if (latestContext == null) {
            log.error("execEventTimeoutTask: Invalid workflow context {}", context.name());
            return task;
        }

        try {
            if (!Objects.equals(latestContext.current(), task.programCounter())) {
                log.error("execEventTimeoutTask: Current worklet({}) is not mismatched with task work({}). Ignored.",
                        latestContext.current(), task.programCounter());
                return task;
            }

            Worklet worklet = workflow.getWorkletInstance(task.programCounter());
            if (worklet == Worklet.Common.COMPLETED || worklet == Worklet.Common.INIT) {
                log.error("execEventTimeoutTask: Current worklet is {}, Ignored", worklet);
                return task;
            }

            initWorkletExecution(latestContext);

            eventMapStore.unregisterEventMap(task.eventType(), latestContext.name());

            log.info("{} worklet.timeout(for event):{}", latestContext.name(), worklet.tag());
            log.trace("{} task:{}, context: {}", latestContext.name(), task, latestContext);

            dataModelInjector.inject(worklet, latestContext);

            WorkletDescription workletDesc = workflow.getWorkletDesc(task.programCounter());
            if (Objects.nonNull(workletDesc)) {
                if (!(workletDesc.tag().equals("INIT") || workletDesc.tag().equals("COMPLETED"))) {
                    staticDataModelInjector.inject(worklet, workletDesc);
                }
            }

            worklet.timeout(latestContext);
            dataModelInjector.inhale(worklet, latestContext);

            log.info("{} worklet.timeout(for event)(done):{}", latestContext.name(), worklet.tag());
            log.trace("{} task:{}, context: {}", latestContext.name(), task, latestContext);


            workplaceStore.commitContext(latestContext.name(), latestContext, latestContext.triggerNext());

        } catch (WorkflowException e) {
            log.error("Exception: ", e);
            latestContext.setCause(e.getMessage());
            latestContext.setState(WorkflowState.EXCEPTION);
            workplaceStore.commitContext(latestContext.name(), latestContext, false);
        } catch (StorageException e) {
            log.error("Exception: ", e);
            // StorageException does not commit context.
        } catch (Exception e) {
            log.error("Exception: ", e);
            latestContext.setCause(e.getMessage());
            latestContext.setState(WorkflowState.EXCEPTION);
            workplaceStore.commitContext(latestContext.name(), latestContext, false);
        }

        return task;
    }

    /**
     * Executes timeout task.
     *
     * @param task time out task
     * @return handler task
     */
    private HandlerTask execTimeoutTask(TimeoutTask task) {

        log.debug("execTimeoutTask- task: {}, hash: {}", task, stringHash(task.context().distributor()));

        WorkflowContext context = (WorkflowContext) (task.context());
        Workflow workflow = workflowStore.get(context.workflowId());
        if (workflow == null) {
            log.error("execTimeoutTask: Invalid workflow {}", context.workflowId());
            return task;
        }

        WorkflowContext latestContext = workplaceStore.getContext(context.name());
        if (latestContext == null) {
            log.error("execTimeoutTask: Invalid workflow context {}", context.name());
            return task;
        }

        try {
            if (!Objects.equals(latestContext.current(), task.programCounter())) {
                log.error("execTimeoutTask: Current worklet({}) is not mismatched with task work({}). Ignored.",
                        latestContext.current(), task.programCounter());
                return task;
            }

            Worklet worklet = workflow.getWorkletInstance(task.programCounter());
            if (worklet == Worklet.Common.COMPLETED || worklet == Worklet.Common.INIT) {
                log.error("execTimeoutTask: Current worklet is {}, Ignored", worklet);
                return task;
            }

            initWorkletExecution(latestContext);

            log.info("{} worklet.timeout:{}", latestContext.name(), worklet.tag());
            log.trace("{} context: {}", latestContext.name(), latestContext);

            dataModelInjector.inject(worklet, latestContext);

            WorkletDescription workletDesc = workflow.getWorkletDesc(task.programCounter());
            if (Objects.nonNull(workletDesc)) {
                if (!(workletDesc.tag().equals("INIT") || workletDesc.tag().equals("COMPLETED"))) {
                    staticDataModelInjector.inject(worklet, workletDesc);
                }
            }

            worklet.timeout(latestContext);
            dataModelInjector.inhale(worklet, latestContext);

            log.info("{} worklet.timeout(done):{}", latestContext.name(), worklet.tag());
            log.trace("{} context: {}", latestContext.name(), latestContext);

            workplaceStore.commitContext(latestContext.name(), latestContext, latestContext.triggerNext());

        } catch (WorkflowException e) {
            log.error("Exception: ", e);
            latestContext.setCause(e.getMessage());
            latestContext.setState(WorkflowState.EXCEPTION);
            workplaceStore.commitContext(latestContext.name(), latestContext, false);
        } catch (StorageException e) {
            log.error("Exception: ", e);
            // StorageException does not commit context.
        } catch (Exception e) {
            log.error("Exception: ", e);
            latestContext.setCause(e.getMessage());
            latestContext.setState(WorkflowState.EXCEPTION);
            workplaceStore.commitContext(latestContext.name(), latestContext, false);
        }

        return task;
    }

    /**
     * Class for delegation of workflow batch execution.
     */
    private class InternalWorkflowBatchDelegate implements WorkflowBatchDelegate {
        @Override
        public void execute(Collection<WorkflowData> operations) {
            log.debug("Execute {} operation(s).", operations.size());

            CompletableFuture.runAsync(() -> {
                List<CompletableFuture<WorkflowData>> futures = operations.stream()
                        .map(
                                x -> CompletableFuture.completedFuture(x)
                                        .thenApplyAsync(WorkFlowEngine.this::execWorkflow, workflowExecutor)
                                        .exceptionally(e -> null)
                        )
                        .collect(Collectors.toList());

                // waiting the completion of futures
                futures.parallelStream().forEach(x -> x.join());

            }, workflowBatchExecutor).exceptionally(e -> {
                log.error("Error submitting batches:", e);
                return null;
            }).thenRun(workflowAccumulator::ready);
        }
    }

    /**
     * Executes workflow.
     *
     * @param dataModelContainer workflow data model container(workflow or workplace)
     * @return
     */
    private WorkflowData execWorkflow(WorkflowData dataModelContainer) {
        if (dataModelContainer instanceof WorkflowContext) {
            return execWorkflowContext((WorkflowContext) dataModelContainer);
        } else if (dataModelContainer instanceof Workplace) {
            return execWorkplace((Workplace) dataModelContainer);
        } else {
            log.error("Invalid context {}", dataModelContainer);
            return null;
        }
    }

    /**
     * Executes workflow context.
     *
     * @param context workflow context
     * @return workflow context
     */
    private WorkflowContext execWorkflowContext(WorkflowContext context) {

        Workflow workflow = workflowStore.get(context.workflowId());
        if (workflow == null) {
            log.error("Invalid workflow {}", context.workflowId());
            return null;
        }

        final WorkflowContext latestContext = workplaceStore.getContext(context.name());
        if (latestContext == null) {
            log.error("Invalid workflow context {}", context.name());
            return null;
        }

        initWorkletExecution(latestContext);

        try {
            final ProgramCounter pc = workflow.next(latestContext);
            final Worklet worklet = workflow.getWorkletInstance(pc);

            if (worklet == Worklet.Common.INIT) {
                log.error("workflow.next gave INIT. It cannot be executed (context: {})", context.name());
                return latestContext;
            }

            latestContext.setCurrent(pc);
            if (worklet == Worklet.Common.COMPLETED) {

                if (workflow.attributes().contains(REMOVE_AFTER_COMPLETE)) {
                    workplaceStore.removeContext(latestContext.name());
                    return null;
                } else {
                    latestContext.setState(WorkflowState.IDLE);
                    workplaceStore.commitContext(latestContext.name(), latestContext, false);
                    return latestContext;
                }
            }

            log.info("{} worklet.process:{}", latestContext.name(), worklet.tag());
            log.trace("{} context: {}", latestContext.name(), latestContext);


            dataModelInjector.inject(worklet, latestContext);

            WorkletDescription workletDesc = workflow.getWorkletDesc(pc);
            if (Objects.nonNull(workletDesc)) {
                if (!(workletDesc.tag().equals("INIT") || workletDesc.tag().equals("COMPLETED"))) {
                    staticDataModelInjector.inject(worklet, workletDesc);
                }
            }

            worklet.process(latestContext);
            dataModelInjector.inhale(worklet, latestContext);

            log.info("{} worklet.process(done): {}", latestContext.name(), worklet.tag());
            log.trace("{} context: {}", latestContext.name(), latestContext);

            if (latestContext.completionEventType() != null) {
                if (latestContext.completionEventGenerator() == null) {
                    String msg = String.format("Invalid exepecting event(%s), generator(%s)",
                            latestContext.completionEventType(),
                            latestContext.completionEventGenerator());
                    throw new WorkflowException(msg);
                }

                registerEventMap(latestContext.completionEventType(), latestContext.completionEventHints(),
                        latestContext.name(), pc);
                latestContext.completionEventGenerator().apply();

                if (latestContext.completionEventTimeout() != 0L) {
                    final EventTimeoutTask eventTimeoutTask = EventTimeoutTask.builder()
                            .context(latestContext)
                            .programCounter(pc)
                            .eventType(latestContext.completionEventType().getName())
                            .eventHintSet(latestContext.completionEventHints())
                            .build();
                    timerChain.schedule(latestContext.completionEventTimeout(),
                            () -> {
                                eventtaskAccumulator.add(eventTimeoutTask);
                            });
                }
            } else {
                if (latestContext.completionEventTimeout() != 0L) {
                    final TimeoutTask timeoutTask = TimeoutTask.builder()
                            .context(latestContext)
                            .programCounter(pc)
                            .build();

                    timerChain.schedule(latestContext.completionEventTimeout(),
                            () -> {
                                eventtaskAccumulator.add(timeoutTask);
                            });
                } else {
                    //completed case
                    // increase program counter
                    latestContext.setCurrent(workflow.increased(pc));
                }
            }
            workplaceStore.commitContext(latestContext.name(), latestContext, latestContext.triggerNext());

        } catch (WorkflowException e) {
            log.error("Exception: ", e);
            latestContext.setCause(e.getMessage());
            latestContext.setState(WorkflowState.EXCEPTION);
            workplaceStore.commitContext(latestContext.name(), latestContext, false);
        } catch (StorageException e) {
            log.error("Exception: ", e);
            // StorageException does not commit context.
        } catch (Exception e) {
            log.error("Exception: ", e);
            latestContext.setCause(e.getMessage());
            latestContext.setState(WorkflowState.EXCEPTION);
            workplaceStore.commitContext(latestContext.name(), latestContext, false);
        }

        return latestContext;
    }

    /**
     * Execute workplace.
     *
     * @param workplace workplace
     * @return workplace
     */
    private Workplace execWorkplace(Workplace workplace) {

        return null;
    }

}