/**
 *
 * Copyright
 * 2009-2015 Jayway Products AB
 * 2016-2017 Föreningen Sambruk
 *
 * Licensed under AGPL, Version 3.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.gnu.org/licenses/agpl.txt
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package se.streamsource.streamflow.infrastructure.event.domain.source.helper;

import org.qi4j.api.configuration.Configuration;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import se.streamsource.streamflow.infrastructure.event.domain.TransactionDomainEvents;
import se.streamsource.streamflow.infrastructure.event.domain.source.EventSource;
import se.streamsource.streamflow.infrastructure.event.domain.source.EventStream;
import se.streamsource.streamflow.infrastructure.event.domain.source.TransactionListener;
import se.streamsource.streamflow.infrastructure.event.domain.source.TransactionVisitor;

/**
 * Helper that enables a service to easily track transactions. Upon startup
 * the tracker will get all the transactions from the store since the last
 * check, and delegate them to the given TransactionVisitor. It will also register itself
 * with the store so that it can get continuous updates.
 *
 * Then, as transactions come in from the store, they will be processed in real-time.
 * If a transaction is successfully handled the configuration of the service, which must
 * extend TransactionTrackerConfiguration, will update the marker for the last successfully handled transaction.
 *
 */
public class TransactionTracker
   implements TransactionListener, TransactionVisitor
{
   private Configuration<? extends TransactionTrackerConfiguration> configuration;
   private TransactionVisitor visitor;
   private EventStream stream;
   private EventSource source;
   private boolean started = false;
   private boolean upToSpeed = false;
   private Logger logger;

   public TransactionTracker( EventStream stream, EventSource source,
                              Configuration<? extends TransactionTrackerConfiguration> configuration,
                              TransactionVisitor visitor )
   {
      this.stream = stream;
      this.configuration = configuration;
      this.visitor = visitor;
      this.source = source;

      logger = LoggerFactory.getLogger( visitor.getClass() );
   }

   public synchronized void start()
   {
      started = true;

      // Get events since last check
      upToSpeed = true; // Pretend that we are up to speed from now on
      source.transactionsAfter( configuration.configuration().lastEventDate().get(), this);
      stream.registerListener( this );
   }

   public synchronized void stop()
   {
      if (started)
      {
         started = false;
         stream.unregisterListener( this );
      }
   }

   public void notifyTransactions( Iterable<TransactionDomainEvents> transactions )
   {
      for (TransactionDomainEvents transactionDomain : transactions)
      {
         if (!visit( transactionDomain ))
            break;
      }
   }

   public synchronized boolean visit( TransactionDomainEvents transactionDomain )
   {
      if (started && configuration.configuration().enabled().get())
      {
         if (!upToSpeed)
         {
            // The tracker has not handled successfully all transactions before,
            // so it needs to get the backlog first

            upToSpeed = true; // Pretend that we are up to speed from now on

            // Get all transactions from last timestamp, including the one in this call
            source.transactionsAfter( configuration.configuration().lastEventDate().get(), this);
            return upToSpeed; // Hopefully we have everything by now
         }

         try
         {
            boolean result = visitor.visit( transactionDomain );

            if (result)
            {
               // Events in this transactionDomain were handled successfully so store new marker
               configuration.configuration().lastEventDate().set( transactionDomain.timestamp().get() );
               configuration.save();
            }

            return result;

         } catch (Throwable e)
         {
            // Events could not be handled so don't update the marker
            logger.error( "Could not handle events", e );

            upToSpeed = false; // We could not handle all transactions, so next time, start from the timestamp

            return false;
         }
      } else
      {
         return false;
      }
   }
}