package org.onlab.onos.net.intent.impl;

import com.google.common.collect.ImmutableList;
import com.google.common.collect.ImmutableMap;
import com.google.common.collect.Lists;
import org.apache.felix.scr.annotations.Activate;
import org.apache.felix.scr.annotations.Component;
import org.apache.felix.scr.annotations.Deactivate;
import org.apache.felix.scr.annotations.Reference;
import org.apache.felix.scr.annotations.ReferenceCardinality;
import org.apache.felix.scr.annotations.Service;
import org.onlab.onos.event.AbstractListenerRegistry;
import org.onlab.onos.event.EventDeliveryService;
import org.onlab.onos.net.flow.CompletedBatchOperation;
import org.onlab.onos.net.flow.FlowRuleBatchOperation;
import org.onlab.onos.net.flow.FlowRuleService;
import org.onlab.onos.net.intent.Intent;
import org.onlab.onos.net.intent.IntentCompiler;
import org.onlab.onos.net.intent.IntentEvent;
import org.onlab.onos.net.intent.IntentException;
import org.onlab.onos.net.intent.IntentExtensionService;
import org.onlab.onos.net.intent.IntentId;
import org.onlab.onos.net.intent.IntentInstaller;
import org.onlab.onos.net.intent.IntentListener;
import org.onlab.onos.net.intent.IntentOperations;
import org.onlab.onos.net.intent.IntentService;
import org.onlab.onos.net.intent.IntentState;
import org.onlab.onos.net.intent.IntentStore;
import org.onlab.onos.net.intent.IntentStoreDelegate;
import org.slf4j.Logger;

import java.util.ArrayList;
import java.util.Iterator;
import java.util.List;
import java.util.Map;
import java.util.Objects;
import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.ConcurrentMap;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Future;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.TimeoutException;

import static com.google.common.base.Preconditions.checkNotNull;
import static java.util.concurrent.Executors.newSingleThreadExecutor;
import static org.onlab.onos.net.intent.IntentState.*;
import static org.onlab.util.Tools.namedThreads;
import static org.slf4j.LoggerFactory.getLogger;

/**
 * An implementation of Intent Manager.
 */
@Component(immediate = true)
@Service
public class IntentManager
        implements IntentService, IntentExtensionService {
    private final Logger log = getLogger(getClass());

    public static final String INTENT_NULL = "Intent cannot be null";
    public static final String INTENT_ID_NULL = "Intent ID cannot be null";

    // Collections for compiler, installer, and listener are ONOS instance local
    private final ConcurrentMap<Class<? extends Intent>,
            IntentCompiler<? extends Intent>> compilers = new ConcurrentHashMap<>();
    private final ConcurrentMap<Class<? extends Intent>,
            IntentInstaller<? extends Intent>> installers = new ConcurrentHashMap<>();

    private final AbstractListenerRegistry<IntentEvent, IntentListener>
            listenerRegistry = new AbstractListenerRegistry<>();

    private ExecutorService executor;
    private ExecutorService monitorExecutor;

    private final IntentStoreDelegate delegate = new InternalStoreDelegate();
    private final TopologyChangeDelegate topoDelegate = new InternalTopoChangeDelegate();

    @Reference(cardinality = ReferenceCardinality.MANDATORY_UNARY)
    protected IntentStore store;

    @Reference(cardinality = ReferenceCardinality.MANDATORY_UNARY)
    protected ObjectiveTrackerService trackerService;

    @Reference(cardinality = ReferenceCardinality.MANDATORY_UNARY)
    protected EventDeliveryService eventDispatcher;

    @Reference(cardinality = ReferenceCardinality.MANDATORY_UNARY)
    protected FlowRuleService flowRuleService;

    @Activate
    public void activate() {
        store.setDelegate(delegate);
        trackerService.setDelegate(topoDelegate);
        eventDispatcher.addSink(IntentEvent.class, listenerRegistry);
        executor = newSingleThreadExecutor(namedThreads("onos-intents"));
        monitorExecutor = newSingleThreadExecutor(namedThreads("onos-intent-monitor"));
        log.info("Started");
    }

    @Deactivate
    public void deactivate() {
        store.unsetDelegate(delegate);
        trackerService.unsetDelegate(topoDelegate);
        eventDispatcher.removeSink(IntentEvent.class);
        executor.shutdown();
        monitorExecutor.shutdown();
        log.info("Stopped");
    }

    @Override
    public void submit(Intent intent) {
        checkNotNull(intent, INTENT_NULL);
        registerSubclassCompilerIfNeeded(intent);
        IntentEvent event = store.createIntent(intent);
        if (event != null) {
            eventDispatcher.post(event);
            executor.execute(new IntentTask(COMPILING, intent));
        }
    }

    @Override
    public void withdraw(Intent intent) {
        checkNotNull(intent, INTENT_NULL);
        executor.execute(new IntentTask(WITHDRAWING, intent));
    }

    // FIXME: implement this method
    @Override
    public Future<IntentOperations> execute(IntentOperations operations) {
        throw new UnsupportedOperationException("execute() is not implemented yet");
    }

    @Override
    public Iterable<Intent> getIntents() {
        return store.getIntents();
    }

    @Override
    public long getIntentCount() {
        return store.getIntentCount();
    }

    @Override
    public Intent getIntent(IntentId id) {
        checkNotNull(id, INTENT_ID_NULL);
        return store.getIntent(id);
    }

    @Override
    public IntentState getIntentState(IntentId id) {
        checkNotNull(id, INTENT_ID_NULL);
        return store.getIntentState(id);
    }

    @Override
    public List<Intent> getInstallableIntents(IntentId intentId) {
        checkNotNull(intentId, INTENT_ID_NULL);
        return store.getInstallableIntents(intentId);
    }

    @Override
    public void addListener(IntentListener listener) {
        listenerRegistry.addListener(listener);
    }

    @Override
    public void removeListener(IntentListener listener) {
        listenerRegistry.removeListener(listener);
    }

    @Override
    public <T extends Intent> void registerCompiler(Class<T> cls, IntentCompiler<T> compiler) {
        compilers.put(cls, compiler);
    }

    @Override
    public <T extends Intent> void unregisterCompiler(Class<T> cls) {
        compilers.remove(cls);
    }

    @Override
    public Map<Class<? extends Intent>, IntentCompiler<? extends Intent>> getCompilers() {
        return ImmutableMap.copyOf(compilers);
    }

    @Override
    public <T extends Intent> void registerInstaller(Class<T> cls, IntentInstaller<T> installer) {
        installers.put(cls, installer);
    }

    @Override
    public <T extends Intent> void unregisterInstaller(Class<T> cls) {
        installers.remove(cls);
    }

    @Override
    public Map<Class<? extends Intent>, IntentInstaller<? extends Intent>> getInstallers() {
        return ImmutableMap.copyOf(installers);
    }

    /**
     * Returns the corresponding intent compiler to the specified intent.
     *
     * @param intent intent
     * @param <T>    the type of intent
     * @return intent compiler corresponding to the specified intent
     */
    private <T extends Intent> IntentCompiler<T> getCompiler(T intent) {
        @SuppressWarnings("unchecked")
        IntentCompiler<T> compiler = (IntentCompiler<T>) compilers.get(intent.getClass());
        if (compiler == null) {
            throw new IntentException("no compiler for class " + intent.getClass());
        }
        return compiler;
    }

    /**
     * Returns the corresponding intent installer to the specified installable intent.
     *
     * @param intent intent
     * @param <T>    the type of installable intent
     * @return intent installer corresponding to the specified installable intent
     */
    private <T extends Intent> IntentInstaller<T> getInstaller(T intent) {
        @SuppressWarnings("unchecked")
        IntentInstaller<T> installer = (IntentInstaller<T>) installers.get(intent.getClass());
        if (installer == null) {
            throw new IntentException("no installer for class " + intent.getClass());
        }
        return installer;
    }

    /**
     * Compiles the specified intent.
     *
     * @param intent intent to be compiled
     */
    private void executeCompilingPhase(Intent intent) {
        // Indicate that the intent is entering the compiling phase.
        store.setState(intent, COMPILING);

        try {
            // Compile the intent into installable derivatives.
            List<Intent> installable = compileIntent(intent);

            // If all went well, associate the resulting list of installable
            // intents with the top-level intent and proceed to install.
            store.addInstallableIntents(intent.id(), installable);
            executeInstallingPhase(intent);

        } catch (Exception e) {
            log.warn("Unable to compile intent {} due to:", intent.id(), e);

            // If compilation failed, mark the intent as failed.
            store.setState(intent, FAILED);
        }
    }

    /**
     * Compiles an intent recursively.
     *
     * @param intent intent
     * @return result of compilation
     */
    private List<Intent> compileIntent(Intent intent) {
        if (intent.isInstallable()) {
            return ImmutableList.of(intent);
        }

        List<Intent> installable = new ArrayList<>();
        // TODO do we need to registerSubclassCompiler?
        for (Intent compiled : getCompiler(intent).compile(intent)) {
            installable.addAll(compileIntent(compiled));
        }

        return installable;
    }

    /**
     * Installs all installable intents associated with the specified top-level
     * intent.
     *
     * @param intent intent to be installed
     */
    private void executeInstallingPhase(Intent intent) {
        // Indicate that the intent is entering the installing phase.
        store.setState(intent, INSTALLING);

        List<FlowRuleBatchOperation> installWork = Lists.newArrayList();
        try {
            List<Intent> installables = store.getInstallableIntents(intent.id());
            if (installables != null) {
                for (Intent installable : installables) {
                    registerSubclassInstallerIfNeeded(installable);
                    trackerService.addTrackedResources(intent.id(),
                                                       installable.resources());
                    List<FlowRuleBatchOperation> batch = getInstaller(installable).install(installable);
                    installWork.addAll(batch);
                }
            }
            // FIXME we have to wait for the installable intents
            //eventDispatcher.post(store.setState(intent, INSTALLED));
            monitorExecutor.execute(new IntentInstallMonitor(intent, installWork, INSTALLED));
        } catch (Exception e) {
            log.warn("Unable to install intent {} due to:", intent.id(), e);
            uninstallIntent(intent, RECOMPILING);

            // If compilation failed, kick off the recompiling phase.
            // FIXME
            //executeRecompilingPhase(intent);
        }
    }

    /**
     * Recompiles the specified intent.
     *
     * @param intent intent to be recompiled
     */
    private void executeRecompilingPhase(Intent intent) {
        // Indicate that the intent is entering the recompiling phase.
        store.setState(intent, RECOMPILING);

        try {
            // Compile the intent into installable derivatives.
            List<Intent> installable = compileIntent(intent);

            // If all went well, compare the existing list of installable
            // intents with the newly compiled list. If they are the same,
            // bail, out since the previous approach was determined not to
            // be viable.
            List<Intent> originalInstallable = store.getInstallableIntents(intent.id());

            if (Objects.equals(originalInstallable, installable)) {
                eventDispatcher.post(store.setState(intent, FAILED));
            } else {
                // Otherwise, re-associate the newly compiled installable intents
                // with the top-level intent and kick off installing phase.
                store.addInstallableIntents(intent.id(), installable);
                executeInstallingPhase(intent);
            }
        } catch (Exception e) {
            log.warn("Unable to recompile intent {} due to:", intent.id(), e);

            // If compilation failed, mark the intent as failed.
            eventDispatcher.post(store.setState(intent, FAILED));
        }
    }

    /**
     * Uninstalls the specified intent by uninstalling all of its associated
     * installable derivatives.
     *
     * @param intent intent to be installed
     */
    private void executeWithdrawingPhase(Intent intent) {
        // Indicate that the intent is being withdrawn.
        store.setState(intent, WITHDRAWING);
        uninstallIntent(intent, WITHDRAWN);

        // If all went well, disassociate the top-level intent with its
        // installable derivatives and mark it as withdrawn.
        // FIXME need to clean up
        //store.removeInstalledIntents(intent.id());
        // FIXME
        //eventDispatcher.post(store.setState(intent, WITHDRAWN));
    }

    /**
     * Uninstalls all installable intents associated with the given intent.
     *
     * @param intent intent to be uninstalled
     */
    private void uninstallIntent(Intent intent, IntentState nextState) {
        List<FlowRuleBatchOperation> uninstallWork = Lists.newArrayList();
        try {
            List<Intent> installables = store.getInstallableIntents(intent.id());
            if (installables != null) {
                for (Intent installable : installables) {
                    List<FlowRuleBatchOperation> batches = getInstaller(installable).uninstall(installable);
                    uninstallWork.addAll(batches);
                }
            }
            monitorExecutor.execute(new IntentInstallMonitor(intent, uninstallWork, nextState));
        } catch (IntentException e) {
            log.warn("Unable to uninstall intent {} due to:", intent.id(), e);
        }
    }

    /**
     * Registers an intent compiler of the specified intent if an intent compiler
     * for the intent is not registered. This method traverses the class hierarchy of
     * the intent. Once an intent compiler for a parent type is found, this method
     * registers the found intent compiler.
     *
     * @param intent intent
     */
    private void registerSubclassCompilerIfNeeded(Intent intent) {
        if (!compilers.containsKey(intent.getClass())) {
            Class<?> cls = intent.getClass();
            while (cls != Object.class) {
                // As long as we're within the Intent class descendants
                if (Intent.class.isAssignableFrom(cls)) {
                    IntentCompiler<?> compiler = compilers.get(cls);
                    if (compiler != null) {
                        compilers.put(intent.getClass(), compiler);
                        return;
                    }
                }
                cls = cls.getSuperclass();
            }
        }
    }

    /**
     * Registers an intent installer of the specified intent if an intent installer
     * for the intent is not registered. This method traverses the class hierarchy of
     * the intent. Once an intent installer for a parent type is found, this method
     * registers the found intent installer.
     *
     * @param intent intent
     */
    private void registerSubclassInstallerIfNeeded(Intent intent) {
        if (!installers.containsKey(intent.getClass())) {
            Class<?> cls = intent.getClass();
            while (cls != Object.class) {
                // As long as we're within the Intent class descendants
                if (Intent.class.isAssignableFrom(cls)) {
                    IntentInstaller<?> installer = installers.get(cls);
                    if (installer != null) {
                        installers.put(intent.getClass(), installer);
                        return;
                    }
                }
                cls = cls.getSuperclass();
            }
        }
    }

    // Store delegate to re-post events emitted from the store.
    private class InternalStoreDelegate implements IntentStoreDelegate {
        @Override
        public void notify(IntentEvent event) {
            eventDispatcher.post(event);
            if (event.type() == IntentEvent.Type.SUBMITTED) {
                executor.execute(new IntentTask(COMPILING, event.subject()));
            }
        }
    }

    // Topology change delegate
    private class InternalTopoChangeDelegate implements TopologyChangeDelegate {
        @Override
        public void triggerCompile(Iterable<IntentId> intentIds,
                                   boolean compileAllFailed) {
            // Attempt recompilation of the specified intents first.
            for (IntentId intentId : intentIds) {
                Intent intent = getIntent(intentId);
                uninstallIntent(intent, RECOMPILING);

                //FIXME
                //executeRecompilingPhase(intent);
            }

            if (compileAllFailed) {
                // If required, compile all currently failed intents.
                for (Intent intent : getIntents()) {
                    if (getIntentState(intent.id()) == FAILED) {
                        executeCompilingPhase(intent);
                    }
                }
            }
        }
    }

    // Auxiliary runnable to perform asynchronous tasks.
    private class IntentTask implements Runnable {
        private final IntentState state;
        private final Intent intent;

        public IntentTask(IntentState state, Intent intent) {
            this.state = state;
            this.intent = intent;
        }

        @Override
        public void run() {
            if (state == COMPILING) {
                executeCompilingPhase(intent);
            } else if (state == RECOMPILING) {
                executeRecompilingPhase(intent);
            } else if (state == WITHDRAWING) {
                executeWithdrawingPhase(intent);
            }
        }
    }

    private class IntentInstallMonitor implements Runnable {

        private final Intent intent;
        private final List<FlowRuleBatchOperation> work;
        private final List<Future<CompletedBatchOperation>> futures;
        private final IntentState nextState;

        public IntentInstallMonitor(Intent intent,
                                    List<FlowRuleBatchOperation> work,
                                    IntentState nextState) {
            this.intent = intent;
            this.work = work;
            // TODO how many Futures can be outstanding? one?
            this.futures = Lists.newLinkedList();
            this.nextState = nextState;

            // TODO need to kick off the first batch sometime, why not now?
            futures.add(applyNextBatch());
        }

        /**
         * Update the intent store with the next status for this intent.
         */
        private void updateIntent() {
            if (nextState == RECOMPILING) {
                executor.execute(new IntentTask(nextState, intent));
            } else if (nextState == INSTALLED || nextState == WITHDRAWN) {
                eventDispatcher.post(store.setState(intent, nextState));
            } else {
                log.warn("Invalid next intent state {} for intent {}", nextState, intent);
            }
        }

        /**
         * Applies the next batch.
         */
        private Future<CompletedBatchOperation> applyNextBatch() {
            if (work.isEmpty()) {
                return null;
            }
            FlowRuleBatchOperation batch = work.remove(0);
            return flowRuleService.applyBatch(batch);
        }

        /**
         * Iterate through the pending futures, and remove them when they have completed.
         */
        private void processFutures() {
            List<Future<CompletedBatchOperation>> newFutures = Lists.newArrayList();
            for (Iterator<Future<CompletedBatchOperation>> i = futures.iterator(); i.hasNext();) {
                Future<CompletedBatchOperation> future = i.next();
                try {
                    // TODO: we may want to get the future here and go back to the future.
                    CompletedBatchOperation completed = future.get(100, TimeUnit.NANOSECONDS);
                    if (completed.isSuccess()) {
                        Future<CompletedBatchOperation> newFuture = applyNextBatch();
                        if (newFuture != null) {
                            // we'll add this later so that we don't get a ConcurrentModException
                            newFutures.add(newFuture);
                        }
                    } else {
                        // TODO check if future succeeded and if not report fail items
                        log.warn("Failed items: {}", completed.failedItems());
                        // TODO revert....
                        //uninstallIntent(intent, RECOMPILING);
                    }
                    i.remove();
                } catch (TimeoutException | InterruptedException | ExecutionException te) {
                    log.debug("Intallations of intent {} is still pending", intent);
                }
            }
            futures.addAll(newFutures);
        }

        @Override
        public void run() {
            processFutures();
            if (futures.isEmpty()) {
                // woohoo! we are done!
                updateIntent();
            } else {
                // resubmit ourselves if we are not done yet
                monitorExecutor.submit(this);
            }
        }
    }
}