/*
    * Copyright 2015 Data Archiving and Networked Services (an institute of
    * Koninklijke Nederlandse Akademie van Wetenschappen), King's College London,
    * Georg-August-Universitaet Goettingen Stiftung Oeffentlichen Rechts
    *
    * Licensed under the EUPL, Version 1.1 or – as soon they will be approved by
    * the European Commission - subsequent versions of the EUPL (the "Licence");
    * You may not use this work except in compliance with the Licence.
    * You may obtain a copy of the Licence at:
   *
   * https://joinup.ec.europa.eu/software/page/eupl
   *
   * Unless required by applicable law or agreed to in writing, software
   * distributed under the Licence is distributed on an "AS IS" basis,
   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   * See the Licence for the specific language governing
   * permissions and limitations under the Licence.
   */
  
  package eu.ehri.project.models.events;
  
  import com.tinkerpop.blueprints.Vertex;
  import com.tinkerpop.frames.Adjacency;
  import com.tinkerpop.frames.Property;
  import com.tinkerpop.frames.modules.javahandler.JavaHandler;
  import com.tinkerpop.frames.modules.javahandler.JavaHandlerContext;
  import com.tinkerpop.pipes.util.Pipeline;
  import eu.ehri.project.definitions.Ontology;
  import eu.ehri.project.models.EntityClass;
  import eu.ehri.project.models.annotations.EntityType;
  import eu.ehri.project.models.annotations.Mandatory;
  import eu.ehri.project.models.base.Entity;
  import eu.ehri.project.models.utils.JavaHandlerUtils;
  
  /**
   * Class representing the system event queue node, of which
   * there Will Be Only One.
   */
  @EntityType(EntityClass.SYSTEM)
  public interface SystemEventQueue extends Entity {
  
      String STREAM_START = Ontology.ACTIONER_HAS_LIFECYCLE_ACTION + "Stream";
  
      /**
       * Fetch the time stamp of the queue initialisation.
       *
       * @return a UTF timestamp string
       */
      @Mandatory
      @Property(Ontology.EVENT_TIMESTAMP)
      String getTimestamp();
  
      /**
       * Fetch the latest global event.
       *
       * @return a system event frame
       */
      @Adjacency(label = STREAM_START)
      SystemEvent getLatestEvent();
  
      /**
       * Get a stream of system events, latest first.
       *
       * @return an iterable of event frames
       */
      @JavaHandler
      Iterable<SystemEvent> getSystemEvents();
  
      abstract class Impl implements JavaHandlerContext<Vertex>, SystemEventQueue {
          public Iterable<SystemEvent> getSystemEvents() {
              Pipeline<Vertex,Vertex> otherPipe = gremlin().as("n")
                      .out(Ontology.ACTIONER_HAS_LIFECYCLE_ACTION)
                      .loop("n", JavaHandlerUtils.noopLoopFunc, JavaHandlerUtils.noopLoopFunc);
              return frameVertices(gremlin()
                      .out(STREAM_START).cast(Vertex.class)
                      .copySplit(gremlin(), otherPipe)
                      .exhaustMerge().cast(Vertex.class));
          }
      }
  }