/// <summary>
/// Add an interval to this representation.
/// </summary>
/// <param name="interval">The interval to add.</param>
/// <param name="direction">Which direction to go - up or down.</param>
/// <returns>Null if there is no supported enharmonically correct representation of the requested interval. For example,
/// adding a minor second to a Bb should return a Cb, but this is not supported so the result will be null. If there is
/// a valid representation (for example, A# plus a minor second correctly yields B) it will be returned.</returns>
public NoteRepresentation AddInterval(Interval interval, IntervalDirection direction = IntervalDirection.Up)
{
var coefficient = direction == IntervalDirection.Up ? 1 : -1;
var newNoteNumber = this.Note.Number + (interval.NumberOfSemitones() * coefficient);
var newNoteName = this.Name.AddNoteNames(interval.NumberOfNoteNames() * coefficient);
var result = new Note(newNoteNumber).GetRepresentations().SingleOrDefault(r => r.Name == newNoteName);
return result;
}