package net.kreatious.pianoleopard.midi.track;
   
   import java.util.HashMap;
   import java.util.Map;
   import java.util.Optional;
   
   import javax.sound.midi.Track;
   
   import net.kreatious.pianoleopard.midi.event.Event;
  import net.kreatious.pianoleopard.midi.event.EventFactory;
  import net.kreatious.pianoleopard.midi.event.EventPair;
  import net.kreatious.pianoleopard.midi.event.TempoCache;
  
  /**
   * Decomposes a {@link Track} into {@link EventPair}s
   *
   * @author Jay-R Studer
   */
  abstract class TrackVisitor {
      private final Map<Object, Event> incompleteEvents = new HashMap<>();
  
      /**
       * Invokes this visitor on the specified track.
       *
       * @param track
       *            the {@link Track} to visit
       * @param cache
       *            the {@link TempoCache} to use for converting timestamps
       */
      public void accept(Track track, TempoCache cache) {
          for (int i = 0; i != track.size(); i++) {
              EventFactory.create(track.get(i), cache).ifPresent(
                      event -> {
                          if (event.isOn()) {
                              incompleteEvents.put(event.getSlot(), event);
                          } else {
                              Optional.ofNullable(incompleteEvents.remove(event.getSlot())).ifPresent(
                                      previousOnEvent -> visitEventPair(new EventPair<>(previousOnEvent, event)));
                          }
                      });
          }
      }
  
      /**
       * Called for each complete pair of events in the current track
       *
       * @param pair
       *            a completed event pair
       */
      protected abstract void visitEventPair(EventPair<? extends Event> pair);
  }