package net.onrc.onos.core.registry;

import java.io.IOException;
import java.util.ArrayList;
import java.util.Collection;
import java.util.Collections;
import java.util.Comparator;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import java.util.Random;
import java.util.concurrent.BlockingQueue;
import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.LinkedBlockingQueue;

import net.floodlightcontroller.core.IFloodlightProviderService;
import net.floodlightcontroller.core.module.FloodlightModuleContext;
import net.floodlightcontroller.core.module.FloodlightModuleException;
import net.floodlightcontroller.core.module.IFloodlightModule;
import net.floodlightcontroller.core.module.IFloodlightService;
import net.floodlightcontroller.restserver.IRestApiService;
import net.onrc.onos.core.registry.web.RegistryWebRoutable;

import org.apache.curator.RetryPolicy;
import org.apache.curator.framework.CuratorFramework;
import org.apache.curator.framework.CuratorFrameworkFactory;
import org.apache.curator.framework.recipes.atomic.AtomicValue;
import org.apache.curator.framework.recipes.atomic.DistributedAtomicLong;
import org.apache.curator.framework.recipes.cache.ChildData;
import org.apache.curator.framework.recipes.cache.PathChildrenCache;
import org.apache.curator.framework.recipes.cache.PathChildrenCache.StartMode;
import org.apache.curator.framework.recipes.cache.PathChildrenCacheEvent;
import org.apache.curator.framework.recipes.cache.PathChildrenCacheListener;
import org.apache.curator.framework.recipes.leader.LeaderLatch;
import org.apache.curator.framework.recipes.leader.LeaderLatchListener;
import org.apache.curator.framework.recipes.leader.Participant;
import org.apache.curator.retry.ExponentialBackoffRetry;
import org.apache.curator.retry.RetryOneTime;
import org.apache.curator.x.discovery.ServiceCache;
import org.apache.curator.x.discovery.ServiceDiscovery;
import org.apache.curator.x.discovery.ServiceDiscoveryBuilder;
import org.apache.curator.x.discovery.ServiceInstance;
import org.openflow.util.HexString;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import com.google.common.base.Charsets;

/**
 * A registry service that uses Zookeeper. All data is stored in Zookeeper,
 * so this can be used as a global registry in a multi-node ONOS cluster.
 * @author jono
 *
 */
public class ZookeeperRegistry implements IFloodlightModule, IControllerRegistryService {

	protected final static Logger log = LoggerFactory.getLogger(ZookeeperRegistry.class);
	protected String controllerId = null;
	
	protected IRestApiService restApi;
	
	//This is the default, it's overwritten by the connectionString configuration parameter
	protected String connectionString = "localhost:2181";
	
	private final String namespace = "onos";
	private final String switchLatchesPath = "/switches";
	private final String CLUSTER_LEADER_PATH = "/cluster/leader";

	private final String SERVICES_PATH = "/"; //i.e. the root of our namespace
	private final String CONTROLLER_SERVICE_NAME = "controllers";
	
	protected CuratorFramework client;
	
	protected PathChildrenCache switchCache;

	protected ConcurrentHashMap<String, SwitchLeadershipData> switches;
	protected Map<String, PathChildrenCache> switchPathCaches;

	protected LeaderLatch clusterLeaderLatch;
	protected ClusterLeaderListener clusterLeaderListener;
	private static final long CLUSTER_LEADER_ELECTION_RETRY_MS = 100;

	private final String ID_COUNTER_PATH = "/flowidcounter";
	private final Long ID_BLOCK_SIZE = 0x100000000L;
	protected DistributedAtomicLong distributedIdCounter;
	
	//Zookeeper performance-related configuration
	protected static final int sessionTimeout = 5000;
	protected static final int connectionTimeout = 7000;

	//
	// Unique ID generation state
	// TODO: The implementation must be updated to use the Zookeeper
	// instead of a ramdon generator.
	//
	private static Random randomGenerator = new Random();
	private static int nextUniqueIdPrefix = 0;
	private static int nextUniqueIdSuffix = 0;

    private final BlockingQueue<SwitchLeaderEvent> switchLeadershipEvents = 
    		new LinkedBlockingQueue<SwitchLeaderEvent>();
    
    private ExecutorService eventThreadExecutorService;
    
    private static class SwitchLeaderEvent {
    	public final long dpid;
    	public final boolean isLeader;
    	
    	public SwitchLeaderEvent(long dpid, boolean isLeader) {
    		this.dpid = dpid;
    		this.isLeader = isLeader;
    	}
    }
    
    /*
     * Dispatcher thread for leadership change events coming from Curator.
     */
    private void dispatchEvents() {
    	while (!Thread.currentThread().isInterrupted()) {
    		try {
    			SwitchLeaderEvent event = switchLeadershipEvents.take();
    			SwitchLeadershipData swData = switches.get(HexString.toHexString(event.dpid));
    			if (swData == null) {
    				log.debug("Leadership data {} not found", event.dpid);
    				continue;
    			}
    			
    			swData.getCallback().controlChanged(event.dpid, event.isLeader);
    		} catch (InterruptedException e) {
    			Thread.currentThread().interrupt();
    			break;
    		} catch (Exception e) {
    			log.error("Exception in registry event thread", e);
    		}
    	}
    }

	protected class SwitchLeaderListener implements LeaderLatchListener{
		String dpid;
		LeaderLatch latch;
		
		public SwitchLeaderListener(String dpid, LeaderLatch latch){
			this.dpid = dpid;
			this.latch = latch;
		}

		@Override
		public void isLeader() {
		    log.debug("Became leader for {}", dpid);
		    
		    switchLeadershipEvents.offer(new SwitchLeaderEvent(HexString.toLong(dpid), true));
		}

		@Override
		public void notLeader() {
		    log.debug("Lost leadership for {}", dpid);
			
			switchLeadershipEvents.offer(new SwitchLeaderEvent(HexString.toLong(dpid), false));
		}
	}
	
	protected class SwitchPathCacheListener implements PathChildrenCacheListener {
		@Override
		public void childEvent(CuratorFramework client,
				PathChildrenCacheEvent event) throws Exception {
			
			String strSwitch = null;
			if (event.getData() != null){
				String[] splitted = event.getData().getPath().split("/");
				strSwitch = splitted[splitted.length - 1];
			}
			
			switch (event.getType()){
			case CHILD_ADDED:
			case CHILD_UPDATED:
				//Check we have a PathChildrenCache for this child, add one if not
				synchronized (switchPathCaches){
					if (switchPathCaches.get(strSwitch) == null){
						PathChildrenCache pc = new PathChildrenCache(client, 
								event.getData().getPath(), true);
						pc.start(StartMode.NORMAL);
						switchPathCaches.put(strSwitch, pc);
					}
				}
				break;
			case CHILD_REMOVED:
				//Remove our PathChildrenCache for this child
				PathChildrenCache pc = null;
				synchronized(switchPathCaches){
					pc = switchPathCaches.remove(strSwitch);
				}
				if (pc != null){
					pc.close();
				}
				break;
			default:
				//All other switchLeadershipEvents are connection status switchLeadershipEvents. We don't need to 
				//do anything as the path cache handles these on its own.
				break;
			}
			
		}
	};

	protected class ClusterLeaderListener implements LeaderLatchListener {
		LeaderLatch latch;

		public ClusterLeaderListener(LeaderLatch latch) {
			this.latch = latch;
		}

		//
		// NOTE: If we need to support callbacks when the
		// leadership changes, those should be called here.
		//
		
		@Override
		public void isLeader() {
			log.debug("Cluster leadership aquired");
		}

		@Override
		public void notLeader() {
			log.debug("Cluster leadership lost");
		}
	}

	/**
	 * Listens for changes to the switch znodes in Zookeeper. This maintains
	 * the second level of PathChildrenCaches that hold the controllers 
	 * contending for each switch - there's one for each switch.
	 */
	PathChildrenCacheListener switchPathCacheListener = new SwitchPathCacheListener();
	protected ServiceDiscovery<ControllerService> serviceDiscovery;
	protected ServiceCache<ControllerService> serviceCache;

	
	@Override
	public void requestControl(long dpid, ControlChangeCallback cb) throws RegistryException {
		log.info("Requesting control for {}", HexString.toHexString(dpid));
		
		if (controllerId == null){
			throw new RuntimeException("Must register a controller before calling requestControl");
		}
		
		String dpidStr = HexString.toHexString(dpid);
		String latchPath = switchLatchesPath + "/" + dpidStr;
		
		if (switches.get(dpidStr) != null){
			log.debug("Already contesting {}, returning", HexString.toHexString(dpid));
			throw new RegistryException("Already contesting control for " + dpidStr);
		}
		
		LeaderLatch latch = new LeaderLatch(client, latchPath, controllerId);
		SwitchLeaderListener listener = new SwitchLeaderListener(dpidStr, latch); 
		latch.addListener(listener);
		

		SwitchLeadershipData swData = new SwitchLeadershipData(latch, cb, listener);
		SwitchLeadershipData oldData = switches.putIfAbsent(dpidStr, swData);
		
		if (oldData != null){
			//There was already data for that key in the map
			//i.e. someone else got here first so we can't succeed
			log.debug("Already requested control for {}", dpidStr);
			throw new RegistryException("Already requested control for " + dpidStr);
		}
		
		//Now that we know we were able to add our latch to the collection,
		//we can start the leader election in Zookeeper. However I don't know
		//how to handle if the start fails - the latch is already in our
		//switches list.
		//TODO seems like there's a Curator bug when latch.start is called when
		//there's no Zookeeper connection which causes two znodes to be put in 
		//Zookeeper at the latch path when we reconnect to Zookeeper.
		try {
			latch.start();
		} catch (Exception e) {
			log.warn("Error starting leader latch: {}", e.getMessage());
			throw new RegistryException("Error starting leader latch for " + dpidStr, e);
		}
		
	}

	@Override
	public void releaseControl(long dpid) {
		log.info("Releasing control for {}", HexString.toHexString(dpid));
		
		String dpidStr = HexString.toHexString(dpid);
		
		SwitchLeadershipData swData = switches.remove(dpidStr);
		
		if (swData == null) {
			log.debug("Trying to release control of a switch we are not contesting");
			return;
		}

		LeaderLatch latch = swData.getLatch();
		
		latch.removeListener(swData.getListener());
		
		try {
			latch.close();
		} catch (IOException e) {
			//I think it's OK not to do anything here. Either the node got 
			//deleted correctly, or the connection went down and the node got deleted.
			log.debug("releaseControl: caught IOException {}", dpidStr);
		}
	}

	@Override
	public boolean hasControl(long dpid) {
		String dpidStr = HexString.toHexString(dpid);
		
		SwitchLeadershipData swData = switches.get(dpidStr);
		
		if (swData == null) {
			log.warn("No leader latch for dpid {}", dpidStr);
			return false;
		}
		
		return swData.getLatch().hasLeadership();
	}

	@Override
	public boolean isClusterLeader() {
	    return clusterLeaderLatch.hasLeadership();
	}

	@Override
	public String getControllerId() {
		return controllerId;
	}
	
	@Override
	public Collection<String> getAllControllers() throws RegistryException {
		log.debug("Getting all controllers");
		
		List<String> controllers = new ArrayList<String>();
		for (ServiceInstance<ControllerService> instance : serviceCache.getInstances()){
			String id = instance.getPayload().getControllerId();
			if (!controllers.contains(id)){
				controllers.add(id);
			}
		}

		return controllers;
	}

	@Override
	public void registerController(String id) throws RegistryException {
		if (controllerId != null) {
			throw new RegistryException(
					"Controller already registered with id " + controllerId);
		}
		
		controllerId = id;
		
		try {
			ServiceInstance<ControllerService> thisInstance = ServiceInstance.<ControllerService>builder()
			        .name(CONTROLLER_SERVICE_NAME)
			        .payload(new ControllerService(controllerId))
			        //.port((int)(65535 * Math.random())) // in a real application, you'd use a common port
			        //.uriSpec(uriSpec)
			        .build();
			
			serviceDiscovery.registerService(thisInstance);
		} catch (Exception e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}
		
	}
	
	@Override
	public String getControllerForSwitch(long dpid) throws RegistryException {
		String dpidStr = HexString.toHexString(dpid);
		
		PathChildrenCache switchCache = switchPathCaches.get(dpidStr);
		
		if (switchCache == null){
			log.warn("Tried to get controller for non-existent switch");
			return null;
		}
		
		try {
			//We've seen issues with these caches get stuck out of date, so we'll have to
			//force them to refresh before each read. This slows down the method as it
			//blocks on a Zookeeper query, however at the moment only the cleanup thread
			//uses this and that isn't particularly time-sensitive.
			switchCache.rebuild();
		} catch (Exception e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}
		
		List<ChildData> sortedData = new ArrayList<ChildData>(switchCache.getCurrentData()); 
		
		Collections.sort(
				sortedData,
				new Comparator<ChildData>(){
					private String getSequenceNumber(String path){
						return path.substring(path.lastIndexOf('-') + 1);
					}
					@Override
					public int compare(ChildData lhs, ChildData rhs) {
						return getSequenceNumber(lhs.getPath()).
								compareTo(getSequenceNumber(rhs.getPath()));
					}
				}
			);
		
		if (sortedData.size() == 0){
			return null;
		}
		
		return new String(sortedData.get(0).getData(), Charsets.UTF_8);
	}
	
	@Override
	public Collection<Long> getSwitchesControlledByController(String controllerId) {
		//TODO remove this if not needed
		throw new RuntimeException("Not yet implemented");
	}
	

	//TODO what should happen when there's no ZK connection? Currently we just return
	//the cache but this may lead to false impressions - i.e. we don't actually know
	//what's in ZK so we shouldn't say we do
	@Override
	public Map<String, List<ControllerRegistryEntry>> getAllSwitches() {
		Map<String, List<ControllerRegistryEntry>> data = 
				new HashMap<String, List<ControllerRegistryEntry>>();
		
		for (Map.Entry<String, PathChildrenCache> entry : switchPathCaches.entrySet()){
			List<ControllerRegistryEntry> contendingControllers =
					 new ArrayList<ControllerRegistryEntry>(); 
			
			if (entry.getValue().getCurrentData().size() < 1){
				//TODO prevent even having the PathChildrenCache in this case
				//log.info("Switch entry with no leader elections: {}", entry.getKey());
				continue;
			}
			
			for (ChildData d : entry.getValue().getCurrentData()) {
			
				String controllerId = new String(d.getData(), Charsets.UTF_8);
				
				String[] splitted = d.getPath().split("-");
				int sequenceNumber = Integer.parseInt(splitted[splitted.length - 1]);
				
				contendingControllers.add(new ControllerRegistryEntry(controllerId, sequenceNumber));
			 }
			
			Collections.sort(contendingControllers);
			data.put(entry.getKey(), contendingControllers);
		}
		return data;
	}
	
        public IdBlock allocateUniqueIdBlock(long range) {
            try {
                AtomicValue<Long> result = null;
                do {
                    result = distributedIdCounter.add(range);
                } while (result == null || !result.succeeded());

                return new IdBlock(result.preValue(), result.postValue() - 1, range);
            } catch (Exception e) {
                log.error("Error allocating ID block");
            }
            return null;
        }
        
	/**
	 * Returns a block of IDs which are unique and unused.
	 * Range of IDs is fixed size and is assigned incrementally as this method called.
	 * Since the range of IDs is managed by Zookeeper in distributed way, this method may block when
	 * requests come up simultaneously.
	 */
        @Override
	public IdBlock allocateUniqueIdBlock(){
            return allocateUniqueIdBlock(ID_BLOCK_SIZE);
	}

	/**
	 * Get a globally unique ID.
	 *
	 * @return a globally unique ID.
	 */
	@Override
	public synchronized long getNextUniqueId() {
		//
		// Generate the next Unique ID.
		//
		// TODO: For now, the higher 32 bits are random, and
		// the lower 32 bits are sequential.
		// The implementation must be updated to use the Zookeeper
		// to allocate the higher 32 bits (globally unique).
		//
		if ((nextUniqueIdSuffix & 0xffffffffL) == 0xffffffffL) {
			nextUniqueIdPrefix = randomGenerator.nextInt();
			nextUniqueIdSuffix = 0;
		} else {
			nextUniqueIdSuffix++;
		}
		long result = (long)nextUniqueIdPrefix << 32;
		result = result | (0xffffffffL & nextUniqueIdSuffix);
		return result;
	}

	/*
	 * IFloodlightModule
	 */
	
	@Override
	public Collection<Class<? extends IFloodlightService>> getModuleServices() {
		Collection<Class<? extends IFloodlightService>> l = 
				new ArrayList<Class<? extends IFloodlightService>>();
		l.add(IControllerRegistryService.class);
		return l;
	}
	
	@Override
	public Map<Class<? extends IFloodlightService>, IFloodlightService> getServiceImpls() {
		Map<Class<? extends IFloodlightService>, IFloodlightService> m = 
				new HashMap<Class<? extends IFloodlightService>, IFloodlightService>();
		m.put(IControllerRegistryService.class,  this);
		return m;
	}
	
	@Override
	public Collection<Class<? extends IFloodlightService>> getModuleDependencies() {
		Collection<Class<? extends IFloodlightService>> l =
                new ArrayList<Class<? extends IFloodlightService>>();
		l.add(IFloodlightProviderService.class);
		l.add(IRestApiService.class);
		return l;
	}
	
	//TODO currently blocks startup when it can't get a Zookeeper connection.
	//Do we support starting up with no Zookeeper connection?
	@Override
	public void init (FloodlightModuleContext context) throws FloodlightModuleException {
		log.info("Initialising the Zookeeper Registry - Zookeeper connection required");
		
		//Read the Zookeeper connection string from the config
		Map<String, String> configParams = context.getConfigParams(this);
		String connectionString = configParams.get("connectionString");
		if (connectionString != null){
			this.connectionString = connectionString;
		}
		log.info("Setting Zookeeper connection string to {}", this.connectionString);

		//
		// Initialize the Unique ID generator
		// TODO: This must be replaced by Zookeeper-based allocation
		//
		nextUniqueIdPrefix = randomGenerator.nextInt();

		restApi = context.getServiceImpl(IRestApiService.class);

		switches = new ConcurrentHashMap<String, SwitchLeadershipData>();
		//switchPathCaches = new HashMap<String, PathChildrenCache>();
		switchPathCaches = new ConcurrentHashMap<String, PathChildrenCache>();
		
		RetryPolicy retryPolicy = new ExponentialBackoffRetry(1000, 3);
		client = CuratorFrameworkFactory.newClient(this.connectionString, 
				sessionTimeout, connectionTimeout, retryPolicy);
		
		client.start();
		client = client.usingNamespace(namespace);

		distributedIdCounter = new DistributedAtomicLong(
				client, 
				ID_COUNTER_PATH, 
				new RetryOneTime(100));
		
		switchCache = new PathChildrenCache(client, switchLatchesPath, true);
		switchCache.getListenable().addListener(switchPathCacheListener);
		
		//Build the service discovery object
	    serviceDiscovery = ServiceDiscoveryBuilder.builder(ControllerService.class)
	            .client(client).basePath(SERVICES_PATH).build();
	    
	    //We read the list of services very frequently (GUI periodically queries them)
	    //so we'll cache them to cut down on Zookeeper queries.
	    serviceCache = serviceDiscovery.serviceCacheBuilder()
				.name(CONTROLLER_SERVICE_NAME).build();
	    
	    
		try {
			serviceDiscovery.start();
			serviceCache.start();
			
			//Don't prime the cache, we want a notification for each child node in the path
			switchCache.start(StartMode.NORMAL);
		} catch (Exception e) {
			throw new FloodlightModuleException("Error initialising ZookeeperRegistry: " 
					+ e.getMessage());
		}
		
		eventThreadExecutorService = Executors.newSingleThreadExecutor();
		eventThreadExecutorService.execute(
				new Runnable() {
					@Override
					public void run(){
						dispatchEvents();
					}
				});
	}

	@Override
	public void startUp (FloodlightModuleContext context) {
		//
		// Cluster Leader election setup.
		// NOTE: We have to do it here, because during the init stage
		// we don't know the Controller ID.
		//
		if (controllerId == null) {
		    log.error("Error on startup: unknown ControllerId");
		}
		clusterLeaderLatch = new LeaderLatch(client,
						     CLUSTER_LEADER_PATH,
						     controllerId);
		clusterLeaderListener = new ClusterLeaderListener(clusterLeaderLatch);
		clusterLeaderLatch.addListener(clusterLeaderListener);
		try {
			clusterLeaderLatch.start();
		} catch (Exception e) {
		    log.error("Error on startup starting the cluster leader election: {}", e.getMessage());
		}

		// Keep trying until there is a cluster leader
		do {
			try {
				Participant leader = clusterLeaderLatch.getLeader();
				if (! leader.getId().isEmpty())
					break;
				Thread.sleep(CLUSTER_LEADER_ELECTION_RETRY_MS);
			} catch (Exception e) {
				log.error("Error on startup waiting for cluster leader election: {}", e.getMessage());
			}
		} while (true);

		restApi.addRestletRoutable(new RegistryWebRoutable());
	}
}