/// <summary>
/// Swaps the positions of two chord notes in the given bar,
/// or in a randomly selected bar if <paramref name="barIndex"/> is null.
/// <para>A random chord in the selected bar is selected, and two randomly
/// selected notes which are played under this chord's time span are swapped
/// by their positions.</para>
/// </summary>
/// <param name="melody"> The candidate melody to operate on.</param>
/// <param name="barIndex"> Index of the bar to do the swap in. If no bar index supplied, then a random bar would be selected. </param>
private protected virtual void SwapTwoNotesMutation(MelodyCandidate melody, int?barIndex = null)
{
// initialization
INote note1, note2;
IList <int> noteIndices;
Random random = new Random();
int note1Index, note2Index, randomIndex1, randomIndex2, chordIndex;
// if no specific bar has been requested then set it randomly
int selectedBarIndex = barIndex ?? random.Next(melody.Bars.Count);
IBar bar = melody.Bars[selectedBarIndex];
chordIndex = random.Next(bar.Chords.Count);
bar.GetOverlappingNotesForChord(chordIndex, out noteIndices);
// assure selected chord in bar contains at least two notes
if (noteIndices.Count < 2)
{
return;
}
// select two random notes from withing the selected chord notes
randomIndex1 = random.Next(1, noteIndices.Count);
randomIndex2 = random.Next(0, randomIndex1);
note1Index = noteIndices[randomIndex1];
note2Index = noteIndices[randomIndex2];
note1 = bar.Notes[note1Index];
note2 = bar.Notes[note2Index];
// swap the notes positions in the bar
bar.Notes.RemoveAt(note1Index);
bar.Notes.Insert(note1Index, note2);
bar.Notes.RemoveAt(note2Index);
bar.Notes.Insert(note2Index, note1);
}