/**
   * Interpolate.
   *
   * @param sequence the sequence
   * @param start the start
   * @param startValue the start value
   * @param stop the stop
   * @param stopValue the stop value
   * @return the edits the list
   */
  private EditList interpolate(
      EditableAnnotatedSequence sequence,
      int start,
      Annotation startValue,
      int stop,
      Annotation stopValue) {

    if (start > stop - 2) throw new IllegalArgumentException("Interval too short");

    if (startValue == null) throw new IllegalArgumentException("Start item does not exist");

    if (stopValue == null) throw new IllegalArgumentException("Stop item does not exist");

    if (startValue.isNull()) throw new IllegalArgumentException("Start value is not set");

    if (stopValue.isNull()) throw new IllegalArgumentException("Stop value is not set");

    float step = 1.0f / (float) (stop - start);
    float value = step;

    Interpolator interpolator = new Interpolator(startValue, stopValue);

    EditList list = new EditList();

    for (int i = start + 1; i < stop; i++) {

      Annotation a = interpolator.interpolate(value);

      if (a == null) continue;

      list.add(new EditableAnnotatedSequence.EditRegionOperation(i, a));

      value += step;
    }

    return list;
  }
  /*
   * (non-Javadoc)
   *
   * @see
   * si.vicos.annotations.editor.tracking.TrackingEditor.EditAssistant#editFrame
   * (si.vicos.annotations.editor.tracking.EditableAnnotatedSequence, int,
   * si.vicos.annotations.Annotation)
   */
  @Override
  public EditList editFrame(EditableAnnotatedSequence sequence, int frame, Annotation region) {

    EditList list = new EditList();

    try {

      list.add(new EditRegionOperation(frame, region));
      list.add(new EditTagAddOperation(frame, "keyframe"));

      // Interpolate forward if possible

      int last = 0;

      for (last = frame + 1; last < sequence.size(); last++)
        if (sequence.hasTag(last, "keyframe") && !sequence.get(last).isNull()) break;

      if (!(last == sequence.size() || frame > last - 2))
        list.addAll(interpolate(sequence, frame, region, last, sequence.get(frame)));

      // Interpolate backwards if possible

      int first = 0;

      for (first = frame - 1; first >= 0; first--)
        if (sequence.hasTag(first, "keyframe") && !sequence.get(first).isNull()) break;

      if (!(first == -1 || first > frame - 2))
        list.addAll(interpolate(sequence, first, sequence.get(first), frame, region));

    } catch (Exception e) {

      Application.getApplicationLogger().report(e);
    }

    return list;
  }