package org.opentrafficsim.sim0mq.publisher;
   
   import java.rmi.RemoteException;
   import java.util.ArrayList;
   import java.util.EnumSet;
   import java.util.LinkedHashMap;
   import java.util.List;
   import java.util.Map;
   
  import org.djutils.exceptions.Throw;
  import org.djutils.event.Event;
  import org.djutils.event.EventListener;
  import org.djutils.event.EventProducer;
  import org.djutils.event.EventType;
  import org.djutils.event.TimedEvent;
  import org.djutils.metadata.MetaData;
  import org.djutils.metadata.ObjectDescriptor;
  import org.djutils.serialization.SerializationException;
  import org.sim0mq.Sim0MQException;
  
  /**
   * Data collection that can be listed and has subscription to change events.
   * <p>
   * Copyright (c) 2020-2024 Delft University of Technology, PO Box 5, 2600 AA, Delft, the Netherlands. All rights reserved. <br>
   * BSD-style license. See <a href="https://opentrafficsim.org/docs/license.html">OpenTrafficSim License</a>.
   * </p>
   * @author <a href="https://github.com/averbraeck">Alexander Verbraeck</a>
   * @author <a href="https://tudelft.nl/staff/p.knoppers-1">Peter Knoppers</a>
   */
  public class SubscriptionHandler
  {
      /** Id of this SubscriptionHandler. */
      private final String id;
  
      /** Transceiver to retrieve the data right now; e.g. GtuIdTransceiver. */
      private final TransceiverInterface listTransceiver;
  
      /** Event producer for add, remove, or change events; e.g. the Network. */
      private final LookupEventProducer eventProducerForAddRemoveOrChange;
  
      /** EventType to subscribe to in order to receive creation of added object events; e.g. Network.GTU_ADD_EVENT. */
      private final EventType addedEventType;
  
      /** EventType to subscribe to in order to receive removed object events; e.g. Network.GTU_REMOVE_EVENT. */
      private final EventType removedEventType;
  
      /** EventType to subscript to in order to receive change of the collection, or object events. */
      private final EventType changeEventType;
  
      /** SubscriptionHandler that handles subscriptions to individual objects; e.g. GTU.MOVE_EVENT. */
      private final SubscriptionHandler elementSubscriptionHandler;
  
      /** The currently active subscriptions. */
      private final Map<ReturnWrapper, Subscription> subscriptions = new LinkedHashMap<>();
  
      /**
       * Create a new SubscriptionHandler.
       * @param id String; id of the new SubscriptionHandler
       * @param listTransceiver TransceiverInterface; transceiver to retrieve the data of <i>the addressed object</i> right now
       * @param eventProducerForAddRemoveOrChange LookupEventProducer; the event producer that can emit the
       *            <code>addedEventType</code>, <code>removedEventType</code>, or <code>changeEventType</code> events
       * @param addedEventType EventType; event type that signals that a new element has been added, should be null if there is no
       *            added event type for the data
       * @param removedEventType EventType; event type that signals that an element has been removed, should be null if there is
       *            no removed event type for the data
       * @param changeEventType EventType; event type that signals that an element has been changed, should be null if there is no
       *            change event type for the data
       * @param elementSubscriptionHandler SubscriptionHandler; SubscriptionHandler for events produced by the underlying elements
       */
      public SubscriptionHandler(final String id, final TransceiverInterface listTransceiver,
              final LookupEventProducer eventProducerForAddRemoveOrChange, final EventType addedEventType,
              final EventType removedEventType, final EventType changeEventType,
              final SubscriptionHandler elementSubscriptionHandler)
      {
          Throw.whenNull(id, "Id may not be null");
          Throw.when(
                  null == eventProducerForAddRemoveOrChange
                          && (addedEventType != null || removedEventType != null || changeEventType != null),
                  NullPointerException.class,
                  "eventProducerForAddRemoveOrChange may not be null when any of those events is non-null");
          this.id = id;
          this.listTransceiver = listTransceiver;
          this.eventProducerForAddRemoveOrChange = eventProducerForAddRemoveOrChange;
          this.addedEventType = addedEventType;
          this.removedEventType = removedEventType;
          this.changeEventType = changeEventType;
          this.elementSubscriptionHandler = elementSubscriptionHandler;
      }
  
      /**
       * Report what payload is required to retrieve a list of all elements, or data and what format a result would have.
       * @return MetaData; description of the payload required to retrieve a list of all elements, or data and what format a
       *         result would have
       */
      public MetaData listRequestMetaData()
      {
          return this.listTransceiver.getAddressFields();
      }
  
     /**
      * Report what the payload format of the result of the list transceiver.
      * @return MetaData; the payload format of the result of the list transceiver
      */
     public MetaData listResultMetaData()
     {
         return this.listTransceiver.getResultFields();
     }
 
     /**
      * Retrieve a data collection.
      * @param address Object[]; address of the requested data collection
      * @param returnWrapper ReturnWrapper; to send back the result
      * @throws RemoteException when communication fails
      * @throws SerializationException on context error
      * @throws Sim0MQException on DSOL error
      */
     public void get(final Object[] address, final ReturnWrapper returnWrapper)
             throws RemoteException, Sim0MQException, SerializationException
     {
         sendResult(this.listTransceiver.get(address, returnWrapper), returnWrapper);
     }
 
     /**
      * Retrieve the list transceiver (only for testing).
      * @return TransceiverInterface; the list transceiver
      */
     public TransceiverInterface getListTransceiver()
     {
         return this.listTransceiver;
     }
 
     /**
      * Return the set of supported commands.
      * @return EnumSet&lt;Command&gt;; the set of supported commands.
      */
     public final EnumSet<Command> subscriptionOptions()
     {
         EnumSet<Command> result = EnumSet.noneOf(Command.class);
         if (null != this.addedEventType)
         {
             result.add(Command.SUBSCRIBE_TO_ADD);
             result.add(Command.UNSUBSCRIBE_FROM_ADD);
         }
         if (null != this.removedEventType)
         {
             result.add(Command.SUBSCRIBE_TO_REMOVE);
             result.add(Command.UNSUBSCRIBE_FROM_REMOVE);
         }
         if (null != this.changeEventType)
         {
             result.add(Command.SUBSCRIBE_TO_CHANGE);
             result.add(Command.UNSUBSCRIBE_FROM_CHANGE);
         }
         if (null != this.listTransceiver)
         {
             result.add(Command.GET_CURRENT);
             result.add(Command.GET_ADDRESS_META_DATA);
             result.add(Command.GET_RESULT_META_DATA);
         }
         return result;
     }
 
     /**
      * Create a new subscription to ADD, REMOVE, or CHANGE events.
      * @param address Object[]; the data that is required to find the correct EventProducer
      * @param eventType EventType; one of the event types that the addressed EventProducer can fire
      * @param returnWrapper ReturnWrapper; generates envelopes for the returned events
      * @throws RemoteException when communication fails
      * @throws SerializationException should never happen
      * @throws Sim0MQException should never happen
      */
     private void subscribeTo(final Object[] address, final EventType eventType, final ReturnWrapper returnWrapper)
             throws RemoteException, Sim0MQException, SerializationException
     {
         if (null == eventType)
         {
             returnWrapper.nack("Does not support subscribe to");
             return;
         }
         String bad = AbstractTransceiver.verifyMetaData(this.eventProducerForAddRemoveOrChange.getAddressMetaData(), address);
         if (bad != null)
         {
             returnWrapper.nack("Bad address: " + bad);
             return;
         }
         EventProducer epi = this.eventProducerForAddRemoveOrChange.lookup(address, returnWrapper);
         if (null == epi)
         {
             // Not necessarily bad; some EventProducers (e.g. GTUs) may disappear at any time
             return; // NACK has been sent by this.eventProducerForAddRemoveOrChange.lookup
         }
         Subscription subscription = this.subscriptions.get(returnWrapper);
         if (null == subscription)
         {
             subscription = new Subscription(returnWrapper);
             this.subscriptions.put(returnWrapper, subscription);
         }
         if (epi.addListener(subscription, eventType))
         {
             returnWrapper.ack("Subscription created");
         }
         else
         {
             // There was already a subscription?
             returnWrapper.ack("There was already such a subscription active");
         }
         // FIXME: if the subscription is an an Object that later disappears, the subscription map will still consume memory for
         // that subscription. That could add up to a lot of memory ...
     }
 
     /**
      * Cancel a subscription to ADD, REMOVE, or CHANGE events.
      * @param address Object[]; the data that is required to find the correct EventProducer
      * @param eventType EventType; one of the event types that the addressed EventProducer can fire
      * @param returnWrapper ReturnWrapper; the ReturnWapper that sent the results until now
      * @throws RemoteException when communication fails
      * @throws SerializationException should never happen
      * @throws Sim0MQException should never happen
      */
     private void unsubscribeFrom(final Object[] address, final EventType eventType, final ReturnWrapper returnWrapper)
             throws RemoteException, Sim0MQException, SerializationException
     {
         if (null == eventType)
         {
             returnWrapper.nack("Does not support unsubscribe from");
             return;
         }
         String bad = AbstractTransceiver.verifyMetaData(this.eventProducerForAddRemoveOrChange.getAddressMetaData(), address);
         if (bad != null)
         {
             returnWrapper.nack("Bad address: " + bad);
             return;
         }
         EventProducer epi = this.eventProducerForAddRemoveOrChange.lookup(address, returnWrapper);
         if (null == epi)
         {
             returnWrapper.nack("Cound not find the event producer of the subscription; has it dissapeared?");
             return;
         }
         Subscription subscription = this.subscriptions.get(returnWrapper);
         if (null == subscription)
         {
             returnWrapper.nack("Cound not find a subscription to cancel");
         }
         else if (!epi.removeListener(subscription, eventType))
         {
             returnWrapper.nack("Subscription was not found");
         }
         else
         {
             this.subscriptions.remove(returnWrapper);
             returnWrapper.ack("Subscription removed");
         }
     }
 
     /**
      * Retrieve the id of this SubscriptionHandler.
      * @return String; the id of this SubscriptionHandler
      */
     public final String getId()
     {
         return this.id;
     }
 
     /**
      * The commands that a SubscriptionHandler understands.
      */
     public enum Command
     {
         /** Subscribe to add events. */
         SUBSCRIBE_TO_ADD,
         /** Subscribe to remove events. */
         SUBSCRIBE_TO_REMOVE,
         /** Subscribe to change events. */
         SUBSCRIBE_TO_CHANGE,
         /** Unsubscribe to add events. */
         UNSUBSCRIBE_FROM_ADD,
         /** Unsubscribe to remove events. */
         UNSUBSCRIBE_FROM_REMOVE,
         /** Unsubscribe to change events. */
         UNSUBSCRIBE_FROM_CHANGE,
         /** Get current set (if a collection), c.q. state (if properties of one object). */
         GET_CURRENT,
         /** Get the address meta data. */
         GET_ADDRESS_META_DATA,
         /** Get the result meta data. */
         GET_RESULT_META_DATA,
         /** Get the output of the IdSource. */
         GET_LIST,
         /** Get the set of implemented commands (must - itself - always be implemented). */
         GET_COMMANDS;
     }
 
     /**
      * Convert a String representing a Command into that Command.
      * @param commandString String; the string
      * @return Command; the corresponding Command, or null if the <code>commandString</code> is not a valid Command
      */
     public static Command lookupCommand(final String commandString)
     {
         if ("GET_ADDRESS_META_DATA".equals(commandString))
         {
             return Command.GET_ADDRESS_META_DATA;
         }
         else if ("GET_CURRENT".equals(commandString))
         {
             return Command.GET_CURRENT;
         }
         else if ("GET_RESULT_META_DATA".equals(commandString))
         {
             return Command.GET_RESULT_META_DATA;
         }
         else if ("GET_RESULT_META_DATA".equals(commandString))
         {
             return Command.GET_RESULT_META_DATA;
         }
         else if ("SUBSCRIBE_TO_ADD".equals(commandString))
         {
             return Command.SUBSCRIBE_TO_ADD;
         }
         else if ("SUBSCRIBE_TO_CHANGE".equals(commandString))
         {
             return Command.SUBSCRIBE_TO_CHANGE;
         }
         else if ("SUBSCRIBE_TO_REMOVE".equals(commandString))
         {
             return Command.SUBSCRIBE_TO_REMOVE;
         }
         else if ("UNSUBSCRIBE_FROM_ADD".equals(commandString))
         {
             return Command.UNSUBSCRIBE_FROM_ADD;
         }
         else if ("UNSUBSCRIBE_FROM_REMOVE".equals(commandString))
         {
             return Command.UNSUBSCRIBE_FROM_REMOVE;
         }
         else if ("UNSUBSCRIBE_FROM_CHANGE".equals(commandString))
         {
             return Command.UNSUBSCRIBE_FROM_CHANGE;
         }
         else if ("GET_LIST".contentEquals(commandString))
         {
             return Command.GET_LIST;
         }
         else if ("GET_COMMANDS".contentEquals(commandString))
         {
             return Command.GET_COMMANDS;
         }
         System.err.println("Could not find command with name \"" + commandString + "\"");
         return null;
     }
 
     /**
      * Execute one command.
      * @param command Command; the command
      * @param address Object[] the address of the object on which the command must be applied
      * @param returnWrapper ReturnWrapper; envelope generator for replies
      * @throws RemoteException on communication failure
      * @throws SerializationException on illegal type in serialization
      * @throws Sim0MQException on communication error
      */
     public void executeCommand(final Command command, final Object[] address, final ReturnWrapper returnWrapper)
             throws RemoteException, Sim0MQException, SerializationException
     {
         Throw.whenNull(command, "Command may not be null");
         Throw.whenNull(returnWrapper, "ReturnWrapper may not be null");
         switch (command)
         {
             case SUBSCRIBE_TO_ADD:
                 subscribeTo(address, this.addedEventType, returnWrapper);
                 break;
 
             case SUBSCRIBE_TO_CHANGE:
                 subscribeTo(address, this.changeEventType, returnWrapper);
                 break;
 
             case SUBSCRIBE_TO_REMOVE:
                 subscribeTo(address, this.removedEventType, returnWrapper);
                 break;
 
             case UNSUBSCRIBE_FROM_ADD:
                 unsubscribeFrom(address, this.addedEventType, returnWrapper);
                 break;
 
             case UNSUBSCRIBE_FROM_CHANGE:
                 unsubscribeFrom(address, this.changeEventType, returnWrapper);
                 break;
 
             case UNSUBSCRIBE_FROM_REMOVE:
                 unsubscribeFrom(address, this.removedEventType, returnWrapper);
                 break;
 
             case GET_CURRENT:
             {
                 Object[] result = this.listTransceiver.get(address, returnWrapper);
                 if (null != result)
                 {
                     sendResult(result, returnWrapper);
                 }
                 // TODO else?
                 break;
             }
 
             case GET_ADDRESS_META_DATA:
                 if (null == this.listTransceiver)
                 {
                     returnWrapper.nack("The " + this.id + " SubscriptionHandler does not support immediate replies");
                 }
                 sendResult(extractObjectDescriptorClassNames(this.listTransceiver.getAddressFields().getObjectDescriptors()),
                         returnWrapper);
                 break;
 
             case GET_RESULT_META_DATA:
                 if (null == this.listTransceiver)
                 {
                     returnWrapper.nack("The " + this.id + " SubscriptionHandler does not support immediate replies");
                 }
                 sendResult(extractObjectDescriptorClassNames(this.listTransceiver.getResultFields().getObjectDescriptors()),
                         returnWrapper);
                 break;
 
             case GET_LIST:
             {
                 if (this.listTransceiver.hasIdSource())
                 {
                     sendResult(this.listTransceiver.getIdSource(address.length, returnWrapper).get(null, returnWrapper),
                             returnWrapper);
                 }
                 else
                 {
                     sendResult(new Object[] {"No list transceiver exists in " + getId()}, returnWrapper);
                 }
                 break;
             }
 
             case GET_COMMANDS:
                 List<String> resultList = new ArrayList<>();
                 if (null != this.addedEventType)
                 {
                     resultList.add(Command.SUBSCRIBE_TO_ADD.toString());
                     resultList.add(Command.UNSUBSCRIBE_FROM_ADD.toString());
                 }
                 if (null != this.removedEventType)
                 {
                     resultList.add(Command.SUBSCRIBE_TO_REMOVE.toString());
                     resultList.add(Command.UNSUBSCRIBE_FROM_REMOVE.toString());
 
                 }
                 if (null != this.changeEventType)
                 {
                     resultList.add(Command.SUBSCRIBE_TO_CHANGE.toString());
                     resultList.add(Command.UNSUBSCRIBE_FROM_CHANGE.toString());
                 }
                 if (this.listTransceiver.getAddressFields() != null)
                 {
                     resultList.add(Command.GET_ADDRESS_META_DATA.toString());
                 }
                 if (this.listTransceiver.getResultFields() != null)
                 {
                     resultList.add(Command.GET_RESULT_META_DATA.toString());
                 }
                 if (null != this.listTransceiver)
                 {
                     resultList.add(Command.GET_LIST.toString());
                 }
                 resultList.add(Command.GET_COMMANDS.toString());
                 Object[] result = new Object[resultList.size()];
                 for (int index = 0; index < result.length; index++)
                 {
                     result[index] = resultList.get(index);
                 }
                 returnWrapper.encodeReplyAndTransmit(result);
                 break;
 
             default:
                 // Cannot happen
                 break;
         }
     }
 
     /**
      * Extract the class names from an array of ObjectDescriptor.
      * @param objectDescriptors ObjectDescriptor[]; the array of ObjectDescriptor
      * @return Object[]; the class names
      */
     private Object[] extractObjectDescriptorClassNames(final ObjectDescriptor[] objectDescriptors)
     {
         Object[] result = new Object[objectDescriptors.length];
         for (int index = 0; index < objectDescriptors.length; index++)
         {
             result[index] = objectDescriptors[index].getObjectClass().getName();
         }
         return result;
     }
 
     /**
      * Send data via Sim0MQ to master if (and only if) it is non-null.
      * @param data Object[]; the data to transmit
      * @param returnWrapper ReturnWrapper; envelope constructor for returned results
      * @throws SerializationException on illegal type in serialization
      * @throws Sim0MQException on communication error
      */
     private void sendResult(final Object[] data, final ReturnWrapper returnWrapper)
             throws Sim0MQException, SerializationException
     {
         if (data != null)
         {
             returnWrapper.encodeReplyAndTransmit(data);
         }
     }
 
     /** {@inheritDoc} */
     @Override
     public String toString()
     {
         return "SubscriptionHandler [id=" + this.id + ", listTransceiver=" + this.listTransceiver
                 + ", eventProducerForAddRemoveOrChange=" + this.eventProducerForAddRemoveOrChange + ", addedEventType="
                 + this.addedEventType + ", removedEventType=" + this.removedEventType + ", changeEventType="
                 + this.changeEventType + ", elementSubscriptionHandler=" + this.elementSubscriptionHandler + "]";
     }
 
 }
 
 /**
  * Handles one subscription.
  */
 class Subscription implements EventListener
 {
     /** ... */
     private static final long serialVersionUID = 20200428L;
 
     /** Generates envelopes for the messages sent over Sim0MQ. */
     private final ReturnWrapper returnWrapper;
 
     /**
      * Construct a new Subscription.
      * @param returnWrapper ReturnWrapper; envelope generator for the messages
      */
     Subscription(final ReturnWrapper returnWrapper)
     {
         this.returnWrapper = returnWrapper;
     }
 
     /** {@inheritDoc} */
     @Override
     public void notify(final Event event) throws RemoteException
     {
         MetaData metaData = event.getType().getMetaData();
         int additionalFields = event.getType() instanceof EventType ? 1 : 0;
         Object[] result = new Object[additionalFields + metaData.size()];
         // result[0] = event.getType().getName();
         if (additionalFields > 0)
         {
             result[0] = ((TimedEvent<?>) event).getTimeStamp();
         }
         Object payload = event.getContent();
         if (payload instanceof Object[])
         {
             for (int index = 0; index < event.getType().getMetaData().size(); index++)
             {
                 result[additionalFields + index] = ((Object[]) payload)[index];
             }
         }
         else
         {
             result[additionalFields] = payload;
         }
         // TODO verify the composition of the result. Problem: no access to the metadata here
         try
         {
             this.returnWrapper.encodeReplyAndTransmit(result);
         }
         catch (Sim0MQException | SerializationException e)
         {
             e.printStackTrace();
         }
     }
 
 }