package net.floodlightcontroller.core.internal;

import java.io.IOException;
import java.util.ArrayList;
import java.util.Collection;
import java.util.Iterator;
import java.util.concurrent.DelayQueue;
import java.util.concurrent.Delayed;
import java.util.concurrent.TimeUnit;

import net.floodlightcontroller.core.IFloodlightProviderService.Role;
import net.floodlightcontroller.core.IOFSwitch;
import net.floodlightcontroller.core.annotations.LogMessageDoc;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

/** 
 * This class handles sending of RoleRequest messages to all connected switches.
 * 
 * Handling Role Requests is tricky. Roles are hard state on the switch and
 * we can't query it so we need to make sure that we have consistent states
 * on the switches. Whenever we send a role request to the set of connected 
 * switches we need to make sure that we've sent the request to all of them 
 * before we process the next change request. If a new switch connects, we 
 * need to send it the current role and need to make sure that the current
 * role doesn't change while we are doing it. We achieve this by synchronizing
 * all these actions on Controller.roleChanger
 * On the receive side: we need to make sure that we receive a reply for each 
 * request we send and that the reply is consistent with the request we sent. 
 * We'd also like to send the role request to the switch asynchronously in a
 * separate thread so we don't block the REST API or other callers.
 * 
 * There are potential ways to relax these synchronization requirements:
 * - "Generation ID" for each role request. However, this would be most useful
 *   if it were global for the whole cluster
 * - Regularly resend the controller's current role. Don't know whether this
 *   might have adverse effects on the switch. 
 *   
 * Caveats:
 * - No way to know if another controller (not in our controller cluster) 
 *   sends MASTER requests to connected switches. Then we would drop to
 *   slave role without knowing it. Could regularly resend the current role. 
 *   Ideally the switch would notify us if it demoted us. What happens if
 *   the other controller also regularly resends the same role request? 
 *   Or if the health check determines that
 *   a controller is dead but the controller is still talking to switches (maybe
 *   just its health check failed) and resending the master role request.... 
 *   We could try to detect if a switch demoted us to slave even if we think
 *   we are master (error messages on packet outs, e.g., when sending LLDPs)
 * 
 *
 * The general model of Role Request handling is as follows:
 * 
 * - All role request messages are handled by this class. Class Controller 
 *   submits a role change request and the request gets queued. submitRequest
 *   takes a Collection of switches to which to send the request. We make a copy
 *   of this list. 
 * - A thread takes these change requests from the queue and sends them to 
 *   all the switches (using our copy of the switch list). 
 * - The OFSwitchImpl sends the request over the wire and puts the request
 *   into a queue of pending request (storing xid and role). We start a timeout 
 *   to make sure we eventually receive a reply from the switch. We use a single
 *   timeout for each request submitted using submitRequest()
 * - After the timeout triggers we go over the list of switches again and
 *   check that a response has been received (by checking the head of the 
 *   OFSwitchImpl's queue of pending requests)
 * - We handle requests and timeouts in the same thread. We use a priority queue
 *   to schedule them so we are guaranteed that they are processed in 
 *   the same order as they are submitted. If a request times out we drop
 *   the connection to this switch. 
 * - Since we decouple submission of role change requests and actually sending
 *   them we cannot check a received role reply against the controller's current 
 *   role because the controller's current role could have changed again. 
 * - Receiving Role Reply messages is handled by OFChannelHandler and
 *   OFSwitchImpl directly. The OFSwitchImpl checks if the received request 
 *   is as expected (xid and role match the head of the pending queue in 
 *   OFSwitchImpl). If so
 *   the switch updates its role. Otherwise the connection is dropped. If this
 *   is the first reply, the SWITCH_SUPPORTS_NX_ROLE attribute is set.
 *   Next, we call addSwitch(), removeSwitch() to update the list of active
 *   switches if appropriate.
 * - If we receive an Error indicating that roles are not supported by the 
 *   switch, we set the SWITCH_SUPPORTS_NX_ROLE to false. We keep the 
 *   switch connection alive while in MASTER and EQUAL role. 
 *   (TODO: is this the right behavior for EQUAL??). If the role changes to
 *   SLAVE the switch connection is dropped (remember: only if the switch
 *   doesn't support role requests)  
 *   The expected behavior is that the switch will probably try to reconnect
 *   repeatedly (with some sort of exponential backoff), but after a  while 
 *   will give-up and move on to the next controller-IP configured on the 
 *   switch. This is the serial failover mechanism from OpenFlow spec v1.0.
 *   
 * New switch connection:
 * - Switch handshake is done without sending any role request messages.
 * - After handshake completes, switch is added to the list of connected switches
 *   and we send the first role request message if role
 *   requests are enabled. If roles are disabled automatically promote switch to
 *   active switch list and clear FlowTable.
 * - When we receive the first reply we proceed as above. In addition, if
 *   the role request is for MASTER we wipe the flow table. We do not wipe
 *   the flow table if the switch connected while role supported was disabled
 *   on the controller. 
 *
 */
public class RoleChanger {
    // FIXME: Upon closer inspection DelayQueue seems to be somewhat broken. 
    // We are required to implement a compareTo based on getDelay() and 
    // getDelay() must return the remaining delay, thus it needs to use the 
    // current time. So x1.compareTo(x1) can never return 0 as some time
    // will have passed between evaluating both getDelays(). This is even worse
    // if the thread happens to be preempted between calling the getDelay()
    // For the time being we enforce a small delay between subsequent
    // role request messages and hope that's long enough to not screw up
    // ordering. In the long run we might want to use two threads and two queues
    // (one for requests, one for timeouts)
    // Sigh. 
    protected DelayQueue<RoleChangeTask> pendingTasks;
    protected long lastSubmitTime;
    protected Thread workerThread;
    protected long timeout;
    protected static long DEFAULT_TIMEOUT = 15L*1000*1000*1000L; // 15s
    protected final static Logger log = LoggerFactory.getLogger(RoleChanger.class);
    /** 
     * A queued task to be handled by the Role changer thread. 
     */
    protected static class RoleChangeTask implements Delayed {
        protected enum Type { 
            /** This is a request. Dispatch the role update to switches */
            REQUEST,
            /** This is a timeout task. Check if all switches have 
                correctly replied to the previously dispatched role request */
            TIMEOUT
        }
        // The set of switches to work on
        public Collection<OFSwitchImpl> switches;
        public Role role;
        public Type type;
        // the time when the task should run as nanoTime() 
        public long deadline;
        public RoleChangeTask(Collection<OFSwitchImpl> switches, Role role, long deadline) {
            this.switches = switches;
            this.role = role;
            this.type = Type.REQUEST;
            this.deadline = deadline;
        }
        @Override
        public int compareTo(Delayed o) {
            Long timeRemaining = getDelay(TimeUnit.NANOSECONDS);
            return timeRemaining.compareTo(o.getDelay(TimeUnit.NANOSECONDS));
        }
        @Override
        public long getDelay(TimeUnit tu) {
            long timeRemaining = deadline - System.nanoTime();
            return tu.convert(timeRemaining, TimeUnit.NANOSECONDS);
        }
    }
    
    @LogMessageDoc(level="ERROR",
                   message="RoleRequestWorker task had an uncaught exception.",
                   explanation="An unknown occured while processing an HA " +
                   		"role change event.",
                   recommendation=LogMessageDoc.GENERIC_ACTION)                              
    protected class RoleRequestWorker extends Thread  {
        @Override
        public void run() {
            RoleChangeTask t;
            boolean interrupted = false;
            log.trace("RoleRequestWorker thread started");
            try {
                while (true) {
                    try {
                        t = pendingTasks.take();
                    } catch (InterruptedException e) {
                        // see http://www.ibm.com/developerworks/java/library/j-jtp05236/index.html
                        interrupted = true;
                        continue;
                    }
                    if (t.type == RoleChangeTask.Type.REQUEST) {
                        sendRoleRequest(t.switches, t.role, t.deadline);
                        // Queue the timeout
                        t.type = RoleChangeTask.Type.TIMEOUT;
                        t.deadline += timeout;
                        pendingTasks.put(t);
                    }
                    else {
                        verifyRoleReplyReceived(t.switches, t.deadline);
                    }
                }
            }
            catch (Exception e) {
                // Should never get here
                log.error("RoleRequestWorker task had an uncaught exception. ", 
                          e);
            }
            finally {
                // Be nice in case we earlier caught InterruptedExecution
                if (interrupted)
                    Thread.currentThread().interrupt();
            }
        } // end loop
    }
    
    public RoleChanger() {
        this.pendingTasks = new DelayQueue<RoleChangeTask>();
        this.workerThread = new Thread(new RoleRequestWorker());
        this.timeout = DEFAULT_TIMEOUT;
        this.workerThread.start();
    }
    
    
    public synchronized void submitRequest(Collection<OFSwitchImpl> switches, Role role) {
        long deadline = System.nanoTime();
        // Grrr. stupid DelayQueue. Make sre we have at least 10ms between 
        // role request messages.
        if (deadline - lastSubmitTime < 10 * 1000*1000) 
            deadline = lastSubmitTime + 10 * 1000*1000;
        // make a copy of the list 
        ArrayList<OFSwitchImpl> switches_copy = new ArrayList<OFSwitchImpl>(switches);
        RoleChangeTask req = new RoleChangeTask(switches_copy, role, deadline);
        pendingTasks.put(req);
        lastSubmitTime = deadline;
    }
    
    /**
     * Send a role request message to switches. This checks the capabilities 
     * of the switch for understanding role request messaging. Currently we only 
     * support the OVS-style role request message, but once the controller 
     * supports OF 1.2, this function will also handle sending out the 
     * OF 1.2-style role request message.
    * @param switches the collection of switches to send the request too
     * @param role the role to request
     */
    @LogMessageDoc(level="WARN",
            message="Failed to send role request message " + 
                    "to switch {switch}: {message}. Disconnecting",
            explanation="An I/O error occurred while attempting to change " +
            		"the switch HA role.",
            recommendation=LogMessageDoc.CHECK_SWITCH)                              
    protected void sendRoleRequest(Collection<OFSwitchImpl> switches,
                                   Role role, long cookie) {
        // There are three cases to consider:
        //
        // 1) If the controller role at the point the switch connected was
        //    null/disabled, then we never sent the role request probe to the
        //    switch and therefore never set the SWITCH_SUPPORTS_NX_ROLE
        //    attribute for the switch, so supportsNxRole is null. In that
        //    case since we're now enabling role support for the controller
        //    we should send out the role request probe/update to the switch.
        //
        // 2) If supportsNxRole == Boolean.TRUE then that means we've already
        //    sent the role request probe to the switch and it replied with
        //    a role reply message, so we know it supports role request
        //    messages. Now we're changing the role and we want to send
        //    it another role request message to inform it of the new role
        //    for the controller.
        //
        // 3) If supportsNxRole == Boolean.FALSE, then that means we sent the
        //    role request probe to the switch but it responded with an error
        //    indicating that it didn't understand the role request message.
        //    In that case we don't want to send it another role request that
        //    it (still) doesn't understand. But if the new role of the
        //    controller is SLAVE, then we don't want the switch to remain
        //    connected to this controller. It might support the older serial
        //    failover model for HA support, so we want to terminate the
        //    connection and get it to initiate a connection with another
        //    controller in its list of controllers. Eventually (hopefully, if
        //    things are configured correctly) it will walk down its list of
        //    controllers and connect to the current master controller.
        Iterator<OFSwitchImpl> iter = switches.iterator();
        while(iter.hasNext()) {
            OFSwitchImpl sw = iter.next();
            try {
                Boolean supportsNxRole = (Boolean)
                        sw.getAttribute(IOFSwitch.SWITCH_SUPPORTS_NX_ROLE);
                if ((supportsNxRole == null) || supportsNxRole) {
                    // Handle cases #1 and #2
                	log.debug("Sending NxRoleRequest to {}", sw);
                    sw.sendNxRoleRequest(role, cookie);
                } else {
                	if (role == Role.MASTER) {
                		// ONOS extension:
                		log.debug("Switch {} doesn't support NxRoleRequests, but sending " + 
                					"{} request anyway", sw, role);
                		//Send the role request anyway, even though we know the switch
                		//doesn't support it. The switch will give an error and in our
                		//error handling code we will add the switch.
                		//NOTE we *could* just add the switch right away rather than
                		//going through the overhead of sending a role request - however
                		//we then have to deal with concurrency issues resulting from
                		//calling addSwitch outside of a netty handler.
                		sw.sendNxRoleRequest(role, cookie);
                	}
                	// Handle case #3
                	else if (role == Role.SLAVE) {
                        log.debug("Disconnecting switch {} that doesn't support " +
                        "role request messages from a controller that went to SLAVE mode");
                        // Closing the channel should result in a call to
                        // channelDisconnect which updates all state 
                        sw.getChannel().close();
                        iter.remove();
                    }
                }
            } catch (IOException e) {
                log.warn("Failed to send role request message " + 
                         "to switch {}: {}. Disconnecting",
                         sw, e);
                sw.getChannel().close();
                iter.remove();
            }
        }
    }
    
    /**
     * Verify that switches have received a role reply message we sent earlier
     * @param switches the collection of switches to send the request too
     * @param cookie the cookie of the request
     */
    @LogMessageDoc(level="WARN",
            message="Timeout while waiting for role reply from switch {switch}."
                    + " Disconnecting",
            explanation="Timed out waiting for the switch to respond to " +
            		"a request to change the HA role.",
            recommendation=LogMessageDoc.CHECK_SWITCH)                              
    protected void verifyRoleReplyReceived(Collection<OFSwitchImpl> switches,
                                   long cookie) {
        for (OFSwitchImpl sw: switches) {
            if (sw.checkFirstPendingRoleRequestCookie(cookie)) {
                sw.getChannel().close();
                log.warn("Timeout while waiting for role reply from switch {}."
                         + " Disconnecting", sw);
            }
        }
    }
}