package net.onrc.onos.ofcontroller.flowmanager;

import java.util.ArrayList;
import java.util.Collection;
import java.util.EnumSet;
import java.util.HashMap;
import java.util.LinkedList;
import java.util.Map;
import java.util.Random;
import java.util.concurrent.Executors;
import java.util.concurrent.ScheduledExecutorService;
import java.util.concurrent.TimeUnit;

import net.floodlightcontroller.core.IFloodlightProviderService;
import net.floodlightcontroller.core.IOFSwitch;
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.floodlightcontroller.util.OFMessageDamper;
import net.onrc.onos.datagrid.IDatagridService;
import net.onrc.onos.graph.GraphDBOperation;
import net.onrc.onos.ofcontroller.core.INetMapStorage;
import net.onrc.onos.ofcontroller.core.INetMapTopologyObjects.IFlowEntry;
import net.onrc.onos.ofcontroller.core.INetMapTopologyObjects.IFlowPath;
import net.onrc.onos.ofcontroller.floodlightlistener.INetworkGraphService;
import net.onrc.onos.ofcontroller.flowmanager.web.FlowWebRoutable;
import net.onrc.onos.ofcontroller.flowprogrammer.IFlowPusherService;
import net.onrc.onos.ofcontroller.topology.ITopologyNetService;
import net.onrc.onos.ofcontroller.topology.Topology;
import net.onrc.onos.ofcontroller.util.*;

import org.openflow.protocol.OFType;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

/**
 * Flow Manager class for handling the network flows.
 */
public class FlowManager implements IFloodlightModule, IFlowService, INetMapStorage {

    //
    // TODO: A temporary variable to switch between the poll-based and
    // notification mechanism for the Flow Manager.
    //
    private final static boolean enableNotifications = false;
    
    // flag to use FlowPusher instead of FlowSwitchOperation/MessageDamper
    private final static boolean enableFlowPusher = false;

    protected GraphDBOperation dbHandlerApi;
    protected GraphDBOperation dbHandlerInner;

    protected volatile IFloodlightProviderService floodlightProvider;
    protected volatile ITopologyNetService topologyNetService;
    protected volatile IDatagridService datagridService;
    protected IRestApiService restApi;
    protected FloodlightModuleContext context;
    protected FlowEventHandler flowEventHandler;

    protected IFlowPusherService pusher;
    
    protected OFMessageDamper messageDamper;
    
    //
    // TODO: Values copied from elsewhere (class LearningSwitch).
    // The local copy should go away!
    //
    protected static final int OFMESSAGE_DAMPER_CAPACITY = 50000; // TODO: find sweet spot
    protected static final int OFMESSAGE_DAMPER_TIMEOUT = 250;	// ms

    // Flow Entry ID generation state
    private static Random randomGenerator = new Random();
    private static int nextFlowEntryIdPrefix = 0;
    private static int nextFlowEntryIdSuffix = 0;
    private static long nextFlowEntryId = 0;

    /** The logger. */
    private final static Logger log = LoggerFactory.getLogger(FlowManager.class);

    // The periodic task(s)
    private ScheduledExecutorService mapReaderScheduler;
    private ScheduledExecutorService shortestPathReconcileScheduler;

    /**
     * Periodic task for reading the Flow Entries and pushing changes
     * into the switches.
     */
    final Runnable mapReader = new Runnable() {
	    public void run() {
		try {
		    runImpl();
		} catch (Exception e) {
		    log.debug("Exception processing All Flow Entries from the Network MAP: ", e);
		    dbHandlerInner.rollback();
		    return;
		}
	    }

	    private void runImpl() {
		long startTime = System.nanoTime();
		int counterAllFlowEntries = 0;
		int counterMyNotUpdatedFlowEntries = 0;

		if (floodlightProvider == null) {
		    log.debug("FloodlightProvider service not found!");
		    return;
		}
		Map<Long, IOFSwitch> mySwitches =
		    floodlightProvider.getSwitches();
		if (mySwitches.isEmpty()) {
			log.trace("No switches controlled");
			return;
		}
		LinkedList<IFlowEntry> addFlowEntries =
		    new LinkedList<IFlowEntry>();
		LinkedList<IFlowEntry> deleteFlowEntries =
		    new LinkedList<IFlowEntry>();

		//
		// Fetch all Flow Entries which need to be updated and select
		// only my Flow Entries that need to be updated into the
		// switches.
		//
		Iterable<IFlowEntry> allFlowEntries =
		    dbHandlerInner.getAllSwitchNotUpdatedFlowEntries();
		for (IFlowEntry flowEntryObj : allFlowEntries) {
		    counterAllFlowEntries++;

		    String dpidStr = flowEntryObj.getSwitchDpid();
		    if (dpidStr == null)
			continue;
		    Dpid dpid = new Dpid(dpidStr);
		    IOFSwitch mySwitch = mySwitches.get(dpid.value());
		    if (mySwitch == null)
			continue;	// Ignore the entry: not my switch

		    IFlowPath flowObj =
			dbHandlerInner.getFlowPathByFlowEntry(flowEntryObj);
		    if (flowObj == null)
			continue;		// Should NOT happen
		    if (flowObj.getFlowId() == null)
			continue;		// Invalid entry

		    //
		    // NOTE: For now we process the DELETE before the ADD
		    // to cover the more common scenario.
		    // TODO: This is error prone and needs to be fixed!
		    //
		    String userState = flowEntryObj.getUserState();
		    if (userState == null)
			continue;
		    if (userState.equals("FE_USER_DELETE")) {
			// An entry that needs to be deleted.
			deleteFlowEntries.add(flowEntryObj);
			installFlowEntry(mySwitch, flowObj, flowEntryObj);
		    } else {
			addFlowEntries.add(flowEntryObj);
		    }
		    counterMyNotUpdatedFlowEntries++;
		}

		//
		// Process the Flow Entries that need to be added
		//
		for (IFlowEntry flowEntryObj : addFlowEntries) {
		    IFlowPath flowObj =
			dbHandlerInner.getFlowPathByFlowEntry(flowEntryObj);
		    if (flowObj == null)
			continue;		// Should NOT happen
		    if (flowObj.getFlowId() == null)
			continue;		// Invalid entry

		    Dpid dpid = new Dpid(flowEntryObj.getSwitchDpid());
		    IOFSwitch mySwitch = mySwitches.get(dpid.value());
		    if (mySwitch == null)
			continue;		// Shouldn't happen
		    installFlowEntry(mySwitch, flowObj, flowEntryObj);
		}

		//
		// Delete all Flow Entries marked for deletion from the
		// Network MAP.
		//
		// TODO: We should use the OpenFlow Barrier mechanism
		// to check for errors, and delete the Flow Entries after the
		// Barrier message is received.
		//
		while (! deleteFlowEntries.isEmpty()) {
		    IFlowEntry flowEntryObj = deleteFlowEntries.poll();
		    IFlowPath flowObj =
			dbHandlerInner.getFlowPathByFlowEntry(flowEntryObj);
		    if (flowObj == null) {
			log.debug("Did not find FlowPath to be deleted");
			continue;
		    }
		    flowObj.removeFlowEntry(flowEntryObj);
		    dbHandlerInner.removeFlowEntry(flowEntryObj);
		}

		dbHandlerInner.commit();

		long estimatedTime = System.nanoTime() - startTime;
		double rate = 0.0;
		if (estimatedTime > 0)
		    rate = ((double)counterAllFlowEntries * 1000000000) / estimatedTime;
		String logMsg = "MEASUREMENT: Processed AllFlowEntries: " +
		    counterAllFlowEntries + " MyNotUpdatedFlowEntries: " +
		    counterMyNotUpdatedFlowEntries + " in " +
		    (double)estimatedTime / 1000000000 + " sec: " +
		    rate + " paths/s";
		log.debug(logMsg);
	    }
	};

    /**
     * Periodic task for reading the Flow Paths and recomputing the
     * shortest paths.
     */
    final Runnable shortestPathReconcile = new Runnable() {
	    public void run() {
		try {
		    runImpl();
		} catch (Exception e) {
		    log.debug("Exception processing All Flows from the Network MAP: ", e);
		    dbHandlerInner.rollback();
		    return;
		}
	    }

	    private void runImpl() {
		long startTime = System.nanoTime();
		int counterAllFlowPaths = 0;
		int counterMyFlowPaths = 0;

		if (floodlightProvider == null) {
		    log.debug("FloodlightProvider service not found!");
		    return;
		}
		Map<Long, IOFSwitch> mySwitches =
		    floodlightProvider.getSwitches();
		if (mySwitches.isEmpty()) {
			log.trace("No switches controlled");
			return;
		}
		LinkedList<IFlowPath> deleteFlows = new LinkedList<IFlowPath>();

		//
		// Fetch and recompute the Shortest Path for those
		// Flow Paths this controller is responsible for.
		//
		Topology topology = topologyNetService.newDatabaseTopology();
		Iterable<IFlowPath> allFlowPaths = dbHandlerInner.getAllFlowPaths();
		for (IFlowPath flowPathObj : allFlowPaths) {
		    counterAllFlowPaths++;
		    if (flowPathObj == null)
			continue;

		    String srcDpidStr = flowPathObj.getSrcSwitch();
		    if (srcDpidStr == null)
			continue;
		    Dpid srcDpid = new Dpid(srcDpidStr);
		    //
		    // Use the source DPID as a heuristic to decide
		    // which controller is responsible for maintaining the
		    // shortest path.
		    // NOTE: This heuristic is error-prone: if the switch
		    // goes away and no controller is responsible for that
		    // switch, then the original Flow Path is not cleaned-up
		    //
		    IOFSwitch mySwitch = mySwitches.get(srcDpid.value());
		    if (mySwitch == null)
			continue;	// Ignore: not my responsibility

		    // Test whether we need to maintain this flow
		    String flowPathTypeStr = flowPathObj.getFlowPathType();
		    if (flowPathTypeStr == null)
			continue;	// Could be invalid entry?
		    if (! flowPathTypeStr.equals("FP_TYPE_SHORTEST_PATH"))
			continue;	// No need to maintain this flow

		    //
		    // Test whether we need to complete the Flow cleanup,
		    // if the Flow has been deleted by the user.
		    //
		    String flowPathUserStateStr = flowPathObj.getFlowPathUserState();
		    if ((flowPathUserStateStr != null)
			&& flowPathUserStateStr.equals("FP_USER_DELETE")) {
			Iterable<IFlowEntry> flowEntries = flowPathObj.getFlowEntries();
			final boolean empty = !flowEntries.iterator().hasNext();
			if (empty)
			    deleteFlows.add(flowPathObj);
		    }

		    // Fetch the fields needed to recompute the shortest path
		    String dataPathSummaryStr = flowPathObj.getDataPathSummary();
		    Short srcPortShort = flowPathObj.getSrcPort();
		    String dstDpidStr = flowPathObj.getDstSwitch();
		    Short dstPortShort = flowPathObj.getDstPort();
		    Long flowPathFlagsLong = flowPathObj.getFlowPathFlags();
		    if ((dataPathSummaryStr == null) ||
			(srcPortShort == null) ||
			(dstDpidStr == null) ||
			(dstPortShort == null) ||
			(flowPathFlagsLong == null)) {
			continue;
		    }

		    Port srcPort = new Port(srcPortShort);
		    Dpid dstDpid = new Dpid(dstDpidStr);
		    Port dstPort = new Port(dstPortShort);
		    SwitchPort srcSwitchPort = new SwitchPort(srcDpid, srcPort);
		    SwitchPort dstSwitchPort = new SwitchPort(dstDpid, dstPort);
		    FlowPathType flowPathType = FlowPathType.valueOf(flowPathTypeStr);
		    FlowPathUserState flowPathUserState = FlowPathUserState.valueOf(flowPathUserStateStr);
		    FlowPathFlags flowPathFlags = new FlowPathFlags(flowPathFlagsLong);

		    counterMyFlowPaths++;

		    //
		    // NOTE: Using here the regular getDatabaseShortestPath()
		    // method won't work here, because that method calls
		    // internally "conn.endTx(Transaction.COMMIT)", and that
		    // will invalidate all handlers to the Titan database.
		    // If we want to experiment with calling here
		    // getDatabaseShortestPath(), we need to refactor that code
		    // to avoid closing the transaction.
		    //
		    DataPath dataPath =
			topologyNetService.getTopologyShortestPath(
				topology,
				srcSwitchPort,
				dstSwitchPort);
		    if (dataPath == null) {
			// We need the DataPath to compare the paths
			dataPath = new DataPath();
			dataPath.setSrcPort(srcSwitchPort);
			dataPath.setDstPort(dstSwitchPort);
		    }
		    dataPath.applyFlowPathFlags(flowPathFlags);

		    String newDataPathSummaryStr = dataPath.dataPathSummary();
		    if (dataPathSummaryStr.equals(newDataPathSummaryStr))
			continue;	// Nothing changed

		    reconcileFlow(flowPathObj, dataPath);
		}

		//
		// Delete all leftover Flows marked for deletion from the
		// Network MAP.
		//
		while (! deleteFlows.isEmpty()) {
		    IFlowPath flowPathObj = deleteFlows.poll();
		    dbHandlerInner.removeFlowPath(flowPathObj);
		}

		topologyNetService.dropTopology(topology);

		dbHandlerInner.commit();

		long estimatedTime = System.nanoTime() - startTime;
		double rate = 0.0;
		if (estimatedTime > 0)
		    rate = ((double)counterAllFlowPaths * 1000000000) / estimatedTime;
		String logMsg = "MEASUREMENT: Processed AllFlowPaths: " +
		    counterAllFlowPaths + " MyFlowPaths: " +
		    counterMyFlowPaths + " in " +
		    (double)estimatedTime / 1000000000 + " sec: " +
		    rate + " paths/s";
		log.debug(logMsg);
	    }
	};


    /**
     * Initialize the Flow Manager.
     *
     * @param conf the Graph Database configuration string.
     */
    @Override
    public void init(String conf) {
    	dbHandlerApi = new GraphDBOperation(conf);
    	dbHandlerInner = new GraphDBOperation(conf);
    }

    /**
     * Shutdown the Flow Manager operation.
     */
    public void finalize() {
    	close();
    }

    /**
     * Shutdown the Flow Manager operation.
     */
    @Override
    public void close() {
	datagridService.deregisterFlowEventHandlerService(flowEventHandler);
    	dbHandlerApi.close();
    	dbHandlerInner.close();
    }

    /**
     * Get the collection of offered module services.
     *
     * @return the collection of offered module services.
     */
    @Override
    public Collection<Class<? extends IFloodlightService>> getModuleServices() {
        Collection<Class<? extends IFloodlightService>> l = 
            new ArrayList<Class<? extends IFloodlightService>>();
        l.add(IFlowService.class);
        return l;
    }

    /**
     * Get the collection of implemented services.
     *
     * @return the collection of implemented services.
     */
    @Override
    public Map<Class<? extends IFloodlightService>, IFloodlightService> 
			       getServiceImpls() {
        Map<Class<? extends IFloodlightService>,
	    IFloodlightService> m =
	    new HashMap<Class<? extends IFloodlightService>,
	    IFloodlightService>();
        m.put(IFlowService.class, this);
        return m;
    }

    /**
     * Get the collection of modules this module depends on.
     *
     * @return the collection of modules this module depends on.
     */
    @Override
    public Collection<Class<? extends IFloodlightService>> 
				      getModuleDependencies() {
	Collection<Class<? extends IFloodlightService>> l =
	    new ArrayList<Class<? extends IFloodlightService>>();
	l.add(IFloodlightProviderService.class);
	l.add(INetworkGraphService.class);
	l.add(IDatagridService.class);
	l.add(IRestApiService.class);
        return l;
    }

    /**
     * Initialize the module.
     *
     * @param context the module context to use for the initialization.
     */
    @Override
    public void init(FloodlightModuleContext context)
	throws FloodlightModuleException {
	this.context = context;
	floodlightProvider = context.getServiceImpl(IFloodlightProviderService.class);
	topologyNetService = context.getServiceImpl(ITopologyNetService.class);
	datagridService = context.getServiceImpl(IDatagridService.class);
	restApi = context.getServiceImpl(IRestApiService.class);

	if (enableFlowPusher) {
		pusher = context.getServiceImpl(IFlowPusherService.class);
	} else {
		messageDamper = new OFMessageDamper(OFMESSAGE_DAMPER_CAPACITY,
	    EnumSet.of(OFType.FLOW_MOD),
	    OFMESSAGE_DAMPER_TIMEOUT);
	}

	this.init("");

	mapReaderScheduler = Executors.newScheduledThreadPool(1);
	shortestPathReconcileScheduler = Executors.newScheduledThreadPool(1);
    }

    /**
     * Get the next Flow Entry ID to use.
     *
     * @return the next Flow Entry ID to use.
     */
    public synchronized long getNextFlowEntryId() {
	//
	// Generate the next Flow Entry ID.
	// NOTE: For now, the higher 32 bits are random, and
	// the lower 32 bits are sequential.
	// In the future, we need a better allocation mechanism.
	//
	if ((nextFlowEntryIdSuffix & 0xffffffffL) == 0xffffffffL) {
	    nextFlowEntryIdPrefix = randomGenerator.nextInt();
	    nextFlowEntryIdSuffix = 0;
	} else {
	    nextFlowEntryIdSuffix++;
	}
	long result = (long)nextFlowEntryIdPrefix << 32;
	result = result | (0xffffffffL & nextFlowEntryIdSuffix);
	return result;
    }

    /**
     * Startup module operation.
     *
     * @param context the module context to use for the startup.
     */
    @Override
    public void startUp(FloodlightModuleContext context) {
	restApi.addRestletRoutable(new FlowWebRoutable());

	// Initialize the Flow Entry ID generator
	nextFlowEntryIdPrefix = randomGenerator.nextInt();
	
	//
	// Create the Flow Event Handler thread and register it with the
	// Datagrid Service
	//
	flowEventHandler = new FlowEventHandler(this, datagridService);
	datagridService.registerFlowEventHandlerService(flowEventHandler);

	// Schedule the threads and periodic tasks
	flowEventHandler.start();
	if (! enableNotifications) {
	    mapReaderScheduler.scheduleAtFixedRate(
			mapReader, 3, 3, TimeUnit.SECONDS);
	    shortestPathReconcileScheduler.scheduleAtFixedRate(
			shortestPathReconcile, 3, 3, TimeUnit.SECONDS);
	}
    }

    /**
     * Add a flow.
     *
     * @param flowPath the Flow Path to install.
     * @param flowId the return-by-reference Flow ID as assigned internally.
     * @return true on success, otherwise false.
     */
    @Override
    public boolean addFlow(FlowPath flowPath, FlowId flowId) {
	//
	// NOTE: We need to explicitly initialize some of the state,
	// in case the application didn't do it.
	//
	for (FlowEntry flowEntry : flowPath.flowEntries()) {
	    if (flowEntry.flowEntrySwitchState() ==
		FlowEntrySwitchState.FE_SWITCH_UNKNOWN) {
		flowEntry.setFlowEntrySwitchState(FlowEntrySwitchState.FE_SWITCH_NOT_UPDATED);
	    }
	    if (! flowEntry.isValidFlowId())
		flowEntry.setFlowId(new FlowId(flowPath.flowId().value()));
	}

	if (FlowDatabaseOperation.addFlow(this, dbHandlerApi, flowPath, flowId)) {
	    datagridService.notificationSendFlowAdded(flowPath);
	    return true;
	}
	return false;
    }

    /**
     * Add a flow entry to the Network MAP.
     *
     * @param flowObj the corresponding Flow Path object for the Flow Entry.
     * @param flowEntry the Flow Entry to install.
     * @return the added Flow Entry object on success, otherwise null.
     */
    private IFlowEntry addFlowEntry(IFlowPath flowObj, FlowEntry flowEntry) {
	return FlowDatabaseOperation.addFlowEntry(this, dbHandlerInner,
						  flowObj, flowEntry);
    }

    /**
     * Delete a flow entry from the Network MAP.
     *
     * @param flowObj the corresponding Flow Path object for the Flow Entry.
     * @param flowEntry the Flow Entry to delete.
     * @return true on success, otherwise false.
     */
    private boolean deleteFlowEntry(IFlowPath flowObj, FlowEntry flowEntry) {
	return FlowDatabaseOperation.deleteFlowEntry(dbHandlerInner,
						     flowObj, flowEntry);
    }

    /**
     * Delete all previously added flows.
     *
     * @return true on success, otherwise false.
     */
    @Override
    public boolean deleteAllFlows() {
	if (FlowDatabaseOperation.deleteAllFlows(dbHandlerApi)) {
	    datagridService.notificationSendAllFlowsRemoved();
	    return true;
	}
	return false;
    }

    /**
     * Delete a previously added flow.
     *
     * @param flowId the Flow ID of the flow to delete.
     * @return true on success, otherwise false.
     */
    @Override
    public boolean deleteFlow(FlowId flowId) {
	if (FlowDatabaseOperation.deleteFlow(dbHandlerApi, flowId)) {
	    datagridService.notificationSendFlowRemoved(flowId);
	    return true;
	}
	return false;
    }

    /**
     * Clear the state for all previously added flows.
     *
     * @return true on success, otherwise false.
     */
    @Override
    public boolean clearAllFlows() {
	if (FlowDatabaseOperation.clearAllFlows(dbHandlerApi)) {
	    datagridService.notificationSendAllFlowsRemoved();
	    return true;
	}
	return false;
    }

    /**
     * Clear the state for a previously added flow.
     *
     * @param flowId the Flow ID of the flow to clear.
     * @return true on success, otherwise false.
     */
    @Override
    public boolean clearFlow(FlowId flowId) {
	if (FlowDatabaseOperation.clearFlow(dbHandlerApi, flowId)) {
	    datagridService.notificationSendFlowRemoved(flowId);
	    return true;
	}
	return false;
    }

    /**
     * Get a previously added flow.
     *
     * @param flowId the Flow ID of the flow to get.
     * @return the Flow Path if found, otherwise null.
     */
    @Override
    public FlowPath getFlow(FlowId flowId) {
	return FlowDatabaseOperation.getFlow(dbHandlerApi, flowId);
    }

    /**
     * Get all installed flows by all installers.
     *
     * @return the Flow Paths if found, otherwise null.
     */
    @Override
    public ArrayList<FlowPath> getAllFlows() {
	return FlowDatabaseOperation.getAllFlows(dbHandlerApi);
    }

    /**
     * Get all previously added flows by a specific installer for a given
     * data path endpoints.
     *
     * @param installerId the Caller ID of the installer of the flow to get.
     * @param dataPathEndpoints the data path endpoints of the flow to get.
     * @return the Flow Paths if found, otherwise null.
     */
    @Override
    public ArrayList<FlowPath> getAllFlows(CallerId installerId,
					   DataPathEndpoints dataPathEndpoints) {
	return FlowDatabaseOperation.getAllFlows(dbHandlerApi, installerId,
						 dataPathEndpoints);
    }

    /**
     * Get all installed flows by all installers for given data path endpoints.
     *
     * @param dataPathEndpoints the data path endpoints of the flows to get.
     * @return the Flow Paths if found, otherwise null.
     */
    @Override
    public ArrayList<FlowPath> getAllFlows(DataPathEndpoints dataPathEndpoints) {
	return FlowDatabaseOperation.getAllFlows(dbHandlerApi,
						 dataPathEndpoints);
    }

    /**
     * Get summary of all installed flows by all installers in a given range.
     *
     * @param flowId the Flow ID of the first flow in the flow range to get.
     * @param maxFlows the maximum number of flows to be returned.
     * @return the Flow Paths if found, otherwise null.
     */
    @Override
    public ArrayList<IFlowPath> getAllFlowsSummary(FlowId flowId,
						   int maxFlows) {
	return FlowDatabaseOperation.getAllFlowsSummary(dbHandlerApi, flowId,
							maxFlows);
    }
    
    /**
     * Get all Flows information, without the associated Flow Entries.
     *
     * @return all Flows information, without the associated Flow Entries.
     */
    public ArrayList<IFlowPath> getAllFlowsWithoutFlowEntries() {
	return FlowDatabaseOperation.getAllFlowsWithoutFlowEntries(dbHandlerApi);
    }

    /**
     * Add and maintain a shortest-path flow.
     *
     * NOTE: The Flow Path argument does NOT contain flow entries.
     *
     * @param flowPath the Flow Path with the endpoints and the match
     * conditions to install.
     * @return the added shortest-path flow on success, otherwise null.
     */
    @Override
    public FlowPath addAndMaintainShortestPathFlow(FlowPath flowPath) {
	//
	// Don't do the shortest path computation here.
	// Instead, let the Flow reconciliation thread take care of it.
	//

	FlowId flowId = new FlowId();
	if (! addFlow(flowPath, flowId))
	    return null;

	return (flowPath);
    }

    /**
     * Get the collection of my switches.
     *
     * @return the collection of my switches.
     */
    public Map<Long, IOFSwitch> getMySwitches() {
	return floodlightProvider.getSwitches();
    }

    /**
     * Get the network topology.
     *
     * @return the network topology.
     */
    public Topology getTopology() {
	return flowEventHandler.getTopology();
    }

    /**
     * Reconcile a flow.
     *
     * @param flowObj the flow that needs to be reconciled.
     * @param newDataPath the new data path to use.
     * @return true on success, otherwise false.
     */
    private boolean reconcileFlow(IFlowPath flowObj, DataPath newDataPath) {
	String flowIdStr = flowObj.getFlowId();

	//
	// Set the incoming port matching and the outgoing port output
	// actions for each flow entry.
	//
	int idx = 0;
	for (FlowEntry flowEntry : newDataPath.flowEntries()) {
	    flowEntry.setFlowId(new FlowId(flowIdStr));

	    // Mark the Flow Entry as not updated in the switch
	    flowEntry.setFlowEntrySwitchState(FlowEntrySwitchState.FE_SWITCH_NOT_UPDATED);
	    // Set the incoming port matching
	    FlowEntryMatch flowEntryMatch = new FlowEntryMatch();
	    flowEntry.setFlowEntryMatch(flowEntryMatch);
	    flowEntryMatch.enableInPort(flowEntry.inPort());

	    //
	    // Set the actions
	    //
	    FlowEntryActions flowEntryActions = flowEntry.flowEntryActions();
	    //
	    // If the first Flow Entry, copy the Flow Path actions to it
	    //
	    if (idx == 0) {
		String actionsStr = flowObj.getActions();
		if (actionsStr != null) {
		    FlowEntryActions flowActions = new FlowEntryActions(actionsStr);
		    for (FlowEntryAction action : flowActions.actions())
			flowEntryActions.addAction(action);
		}
	    }
	    idx++;
	    //
	    // Add the outgoing port output action
	    //
	    FlowEntryAction flowEntryAction = new FlowEntryAction();
	    flowEntryAction.setActionOutput(flowEntry.outPort());
	    flowEntryActions.addAction(flowEntryAction);
	}

	//
	// Remove the old Flow Entries, and add the new Flow Entries
	//
	Iterable<IFlowEntry> flowEntries = flowObj.getFlowEntries();
	for (IFlowEntry flowEntryObj : flowEntries) {
	    flowEntryObj.setUserState("FE_USER_DELETE");
	    flowEntryObj.setSwitchState("FE_SWITCH_NOT_UPDATED");
	}
	for (FlowEntry flowEntry : newDataPath.flowEntries()) {
	    addFlowEntry(flowObj, flowEntry);
	}

	//
	// Set the Data Path Summary
	//
	String dataPathSummaryStr = newDataPath.dataPathSummary();
	flowObj.setDataPathSummary(dataPathSummaryStr);

	return true;
    }

    /**
     * Reconcile all flows in a set.
     *
     * @param flowObjSet the set of flows that need to be reconciliated.
     */
    private void reconcileFlows(Iterable<IFlowPath> flowObjSet) {
	if (! flowObjSet.iterator().hasNext())
	    return;
	// TODO: Not implemented/used yet.
    }

    /**
     * Install a Flow Entry on a switch.
     *
     * @param mySwitch the switch to install the Flow Entry into.
     * @param flowObj the flow path object for the flow entry to install.
     * @param flowEntryObj the flow entry object to install.
     * @return true on success, otherwise false.
     */
    private boolean installFlowEntry(IOFSwitch mySwitch, IFlowPath flowObj,
				    IFlowEntry flowEntryObj) {
    	if (enableFlowPusher) {
        	return pusher.add(mySwitch, flowObj, flowEntryObj);
    	} else {
    		return FlowSwitchOperation.installFlowEntry(
    			floodlightProvider.getOFMessageFactory(),
    			messageDamper, mySwitch, flowObj, flowEntryObj);
    	}
    }

    /**
     * Install a Flow Entry on a switch.
     *
     * @param mySwitch the switch to install the Flow Entry into.
     * @param flowPath the flow path for the flow entry to install.
     * @param flowEntry the flow entry to install.
     * @return true on success, otherwise false.
     */
    private boolean installFlowEntry(IOFSwitch mySwitch, FlowPath flowPath,
				    FlowEntry flowEntry) {
    	if (enableFlowPusher) {
        	return pusher.add(mySwitch, flowPath, flowEntry);
    	} else {
    		return FlowSwitchOperation.installFlowEntry(
    		floodlightProvider.getOFMessageFactory(),
    		messageDamper, mySwitch, flowPath, flowEntry);
    	}
    }

    /**
     * Remove a Flow Entry from a switch.
     *
     * @param mySwitch the switch to remove the Flow Entry from.
     * @param flowPath the flow path for the flow entry to remove.
     * @param flowEntry the flow entry to remove.
     * @return true on success, otherwise false.
     */
    private boolean removeFlowEntry(IOFSwitch mySwitch, FlowPath flowPath,
				   FlowEntry flowEntry) {
	//
	// The installFlowEntry() method implements both installation
	// and removal of flow entries.
	//
	return (installFlowEntry(mySwitch, flowPath, flowEntry));
    }

    /**
     * Push modified Flow Entries to switches.
     *
     * NOTE: Only the Flow Entries to switches controlled by this instance
     * are pushed.
     *
     * @param modifiedFlowEntries the collection of modified Flow Entries.
     */
    public void pushModifiedFlowEntriesToSwitches(
			Collection<FlowPathEntryPair> modifiedFlowEntries) {
	// TODO: For now, the pushing of Flow Entries is disabled
	if (! enableNotifications)
	    return;

	if (modifiedFlowEntries.isEmpty())
	    return;

	Map<Long, IOFSwitch> mySwitches = getMySwitches();

	for (FlowPathEntryPair flowPair : modifiedFlowEntries) {
	    FlowPath flowPath = flowPair.flowPath;
	    FlowEntry flowEntry = flowPair.flowEntry;

	    IOFSwitch mySwitch = mySwitches.get(flowEntry.dpid().value());
	    if (mySwitch == null)
		continue;

	    log.debug("Pushing Flow Entry To Switch: {}", flowEntry.toString());

	    //
	    // Install the Flow Entry into the switch
	    //
	    if (! installFlowEntry(mySwitch, flowPath, flowEntry)) {
		String logMsg = "Cannot install Flow Entry " +
		    flowEntry.flowEntryId() +
		    " from Flow Path " + flowPath.flowId() +
		    " on switch " + flowEntry.dpid();
		log.error(logMsg);
		continue;
	    }

	    //
	    // NOTE: Here we assume that the switch has been
	    // successfully updated.
	    //
	    flowEntry.setFlowEntrySwitchState(FlowEntrySwitchState.FE_SWITCH_UPDATED);
	}
    }

    /**
     * Push modified Flow Entries to the datagrid.
     *
     * @param modifiedFlowEntries the collection of modified Flow Entries.
     */
    public void pushModifiedFlowEntriesToDatagrid(
			Collection<FlowPathEntryPair> modifiedFlowEntries) {
	// TODO: For now, the pushing of Flow Entries is disabled
	if (! enableNotifications)
	    return;

	if (modifiedFlowEntries.isEmpty())
	    return;

	Map<Long, IOFSwitch> mySwitches = getMySwitches();

	for (FlowPathEntryPair flowPair : modifiedFlowEntries) {
	    FlowEntry flowEntry = flowPair.flowEntry;

	    IOFSwitch mySwitch = mySwitches.get(flowEntry.dpid().value());

	    //
	    // TODO: For now Flow Entries are removed by all instances,
	    // even if this Flow Entry is not for our switches.
	    //
	    // This is needed to handle the case a switch going down:
	    // it has no Master controller instance, hence no
	    // controller instance will cleanup its flow entries.
	    // This is sub-optimal: we need to elect a controller
	    // instance to handle the cleanup of such orphaned flow
	    // entries.
	    //
	    if (mySwitch == null) {
		if (flowEntry.flowEntryUserState() !=
		    FlowEntryUserState.FE_USER_DELETE) {
		    continue;
		}
		if (! flowEntry.isValidFlowEntryId())
		    continue;
	    }

	    log.debug("Pushing Flow Entry To Datagrid: {}", flowEntry.toString());
	    //
	    // Write the Flow Entry to the Datagrid
	    //
	    switch (flowEntry.flowEntryUserState()) {
	    case FE_USER_ADD:
		if (mySwitch == null)
		    break;	// Install only flow entries for my switches
		datagridService.notificationSendFlowEntryAdded(flowEntry);
		break;
	    case FE_USER_MODIFY:
		if (mySwitch == null)
		    break;	// Install only flow entries for my switches
		datagridService.notificationSendFlowEntryUpdated(flowEntry);
		break;
	    case FE_USER_DELETE:
		datagridService.notificationSendFlowEntryRemoved(flowEntry.flowEntryId());
		break;
	    }
	}
    }

    /**
     * Push Flow Entries to the Network MAP.
     *
     * NOTE: The Flow Entries are pushed only on the instance responsible
     * for the first switch. This is to avoid database errors when multiple
     * instances are writing Flow Entries for the same Flow Path.
     *
     * @param modifiedFlowEntries the collection of Flow Entries to push.
     */
    public void pushModifiedFlowEntriesToDatabase(
		Collection<FlowPathEntryPair> modifiedFlowEntries) {
	// TODO: For now, the pushing of Flow Entries is disabled
	if (! enableNotifications)
	    return;

	if (modifiedFlowEntries.isEmpty())
	    return;

	Map<Long, IOFSwitch> mySwitches = getMySwitches();

	for (FlowPathEntryPair flowPair : modifiedFlowEntries) {
	    FlowPath flowPath = flowPair.flowPath;
	    FlowEntry flowEntry = flowPair.flowEntry;

	    if (! flowEntry.isValidFlowEntryId())
		continue;

	    //
	    // Push the changes only on the instance responsible for the
	    // first switch.
	    //
	    Dpid srcDpid = flowPath.dataPath().srcPort().dpid();
	    IOFSwitch mySrcSwitch = mySwitches.get(srcDpid.value());
	    if (mySrcSwitch == null)
		continue;

	    log.debug("Pushing Flow Entry To Database: {}", flowEntry.toString());
	    //
	    // Write the Flow Entry to the Network Map
	    //
	    // NOTE: We try a number of times, in case somehow some other
	    // instances are writing at the same time.
	    // Apparently, if other instances are writing at the same time
	    // this will trigger an error.
	    //
	    for (int i = 0; i < 6; i++) {
		try {
		    //
		    // Find the Flow Path in the Network MAP.
		    //
		    // NOTE: The Flow Path might not be found if the Flow was
		    // just removed by some other controller instance.
		    //
		    IFlowPath flowObj =
			dbHandlerInner.searchFlowPath(flowEntry.flowId());
		    if (flowObj == null) {
			String logMsg = "Cannot find Network MAP entry for Flow Path " + flowEntry.flowId();
			log.error(logMsg);
			break;
		    }

		    // Write the Flow Entry
		    switch (flowEntry.flowEntryUserState()) {
		    case FE_USER_ADD:
			// FALLTHROUGH
		    case FE_USER_MODIFY:
			if (addFlowEntry(flowObj, flowEntry) == null) {
			    String logMsg = "Cannot write to Network MAP Flow Entry " +
				flowEntry.flowEntryId() +
				" from Flow Path " + flowEntry.flowId() +
				" on switch " + flowEntry.dpid();
			    log.error(logMsg);
			}
			break;
		    case FE_USER_DELETE:
			if (deleteFlowEntry(flowObj, flowEntry) == false) {
			    String logMsg = "Cannot remove from Network MAP Flow Entry " +
				flowEntry.flowEntryId() +
				" from Flow Path " + flowEntry.flowId() +
				" on switch " + flowEntry.dpid();
			    log.error(logMsg);
			}
			break;
		    }

		    // Commit to the database
		    dbHandlerInner.commit();
		    break;	// Success

		} catch (Exception e) {
		    log.debug("Exception writing Flow Entry to Network MAP: ", e);
		    dbHandlerInner.rollback();
		    // Wait a bit (random value [1ms, 20ms] and try again
		    int delay = 1 + randomGenerator.nextInt() % 20;
		    try {
			Thread.sleep(delay);
		    } catch (Exception e0) {
		    }
		}
	    }
	}
    }
}