refactor: PositionedNote composition with Note instead of inheritance

lib/src/note/note.dart

@@ -69,7 +69,7 @@ final class Note implements MusicItem, Transposable<Note> {
   /// Note.eFlat.difference(Note.bFlat) == 7
   /// Note.a.difference(Note.g) == -2
   /// ```
-  int difference(covariant Note other) => other.semitones - semitones;
+  int difference(Note other) => other.semitones - semitones;
 
   /// Returns this [Note] positioned in the given [octave] as [PositionedNote].
   ///
@@ -80,8 +80,7 @@ final class Note implements MusicItem, Transposable<Note> {
   /// Note.aFlat.inOctave(2)
   ///   == const PositionedNote(Notes.a, Accidental.flat, 2);
   /// ```
-  PositionedNote inOctave(int octave) =>
-      PositionedNote(note, accidental, octave);
+  PositionedNote inOctave(int octave) => PositionedNote(this, octave);
 
   /// Returns the distance in relation to the circle of fifths.
   ///

lib/src/note/positioned_note.dart

@@ -1,12 +1,15 @@
 part of '../../music_notes.dart';
 
 /// A note octave in the octave range.
-final class PositionedNote extends Note {
-  /// The octave where this [PositionedNote] is.
+final class PositionedNote implements MusicItem, Transposable<PositionedNote> {
+  /// Which of the 12 notes inside the octave.
+  final Note note;
+
+  /// The octave where the [note] is positioned.
   final int octave;
 
   /// Creates a new [PositionedNote] from [Note] arguments and [octave].
-  const PositionedNote(super.note, [super.accidental, this.octave = 4]);
+  const PositionedNote(this.note, [this.octave = 4]);
 
   /// Returns the [octave] that corresponds to the semitones from root height.
   ///
@@ -29,7 +32,8 @@ final class PositionedNote extends Note {
   /// Note.a.inOctave(2).semitonesFromRootHeight == 34
   /// Note.c.inOctave(0).semitonesFromRootHeight == 1
   /// ```
-  int get semitonesFromRootHeight => semitones + octave * chromaticDivisions;
+  @override
+  int get semitones => note.semitones + octave * chromaticDivisions;
 
   /// Returns the difference in semitones between this [PositionedNote] and
   /// [other].
@@ -40,9 +44,7 @@ final class PositionedNote extends Note {
   /// Note.eFlat.inOctave(4).difference(Note.bFlat.inOctave(4)) == 7
   /// Note.a.inOctave(4).difference(Note.g.inOctave(4)) == -2
   /// ```
-  @override
-  int difference(covariant PositionedNote other) =>
-      other.semitonesFromRootHeight - semitonesFromRootHeight;
+  int difference(PositionedNote other) => other.semitones - semitones;
 
   /// Returns a transposed [PositionedNote] by [interval]
   /// from this [PositionedNote].
@@ -56,16 +58,16 @@ final class PositionedNote extends Note {
   /// ```
   @override
   PositionedNote transposeBy(Interval interval) {
-    final transposedNote = super.transposeBy(interval);
+    final transposedNote = note.transposeBy(interval);
 
     return transposedNote.inOctave(
       octaveFromSemitones(
-        semitonesFromRootHeight +
+        semitones +
             interval.semitones -
-            // We don't want to take the accidental into account when
-            // calculating the octave height, as it depends on the note name.
-            // This correctly handles cases with the same number of accidentals
-            // but different octaves (e.g., C♭4 but B3).
+// We don't want to take the accidental into account when
+// calculating the octave height, as it depends on the note name.
+// This correctly handles cases with the same number of accidentals
+// but different octaves (e.g., C♭4 but B3).
             transposedNote.accidental.semitones,
       ),
     );
@@ -110,8 +112,8 @@ final class PositionedNote extends Note {
   /// Note.a.inOctave(3).scientificName == 'A3'
   /// Note.bFlat.inOctave(1).scientificName == 'B♭1'
   /// ```
-  String get scientificName => '${note.name.toUpperCase()}'
-      '${accidental != Accidental.natural ? accidental.symbol : ''}'
+  String get scientificName => '${note.note.name.toUpperCase()}'
+      '${note.accidental != Accidental.natural ? note.accidental.symbol : ''}'
       '$octave';
 
   /// Returns the string representation of this [Note] following
@@ -125,17 +127,17 @@ final class PositionedNote extends Note {
   /// ```
   String get helmholtzName {
     final accidentalSymbol =
-        accidental != Accidental.natural ? accidental.symbol : '';
+        note.accidental != Accidental.natural ? note.accidental.symbol : '';
 
     if (octave >= 3) {
       const superPrime = '′';
 
-      return '${note.name}$accidentalSymbol${superPrime * (octave - 3)}';
+      return '${note.note.name}$accidentalSymbol${superPrime * (octave - 3)}';
     }
 
     const subPrime = '͵';
 
-    return '${note.name.toUpperCase()}$accidentalSymbol'
+    return '${note.note.name.toUpperCase()}$accidentalSymbol'
         '${subPrime * (octave - 2).abs()}';
   }
 
@@ -144,15 +146,14 @@ final class PositionedNote extends Note {
 
   @override
   bool operator ==(Object other) =>
-      super == other && other is PositionedNote && octave == other.octave;
+      other is PositionedNote && note == other.note && octave == other.octave;
 
   @override
   int get hashCode => Object.hash(super.hashCode, octave);
 
   @override
   int compareTo(covariant PositionedNote other) => compareMultiple([
         () => octave.compareTo(other.octave),
-        () => semitones.compareTo(other.semitones),
-        () => note.value.compareTo(other.note.value),
+        () => note.compareTo(other.note),
       ]);
 }

test/src/note/positioned_note_test.dart

@@ -30,17 +30,17 @@ void main() {
         'should return the semitones from the root height of this '
         'PositionedNote',
         () {
-          expect(Note.c.inOctave(-4).semitonesFromRootHeight, -47);
-          expect(Note.a.inOctave(-4).semitonesFromRootHeight, -38);
-          expect(Note.c.inOctave(-3).semitonesFromRootHeight, -35);
-          expect(Note.c.inOctave(-2).semitonesFromRootHeight, -23);
-          expect(Note.c.inOctave(-1).semitonesFromRootHeight, -11);
-          expect(Note.c.inOctave(0).semitonesFromRootHeight, 1);
-          expect(Note.c.inOctave(1).semitonesFromRootHeight, 13);
-          expect(Note.c.inOctave(2).semitonesFromRootHeight, 25);
-          expect(Note.a.inOctave(2).semitonesFromRootHeight, 34);
-          expect(Note.c.inOctave(3).semitonesFromRootHeight, 37);
-          expect(Note.a.inOctave(4).semitonesFromRootHeight, 58);
+          expect(Note.c.inOctave(-4).semitones, -47);
+          expect(Note.a.inOctave(-4).semitones, -38);
+          expect(Note.c.inOctave(-3).semitones, -35);
+          expect(Note.c.inOctave(-2).semitones, -23);
+          expect(Note.c.inOctave(-1).semitones, -11);
+          expect(Note.c.inOctave(0).semitones, 1);
+          expect(Note.c.inOctave(1).semitones, 13);
+          expect(Note.c.inOctave(2).semitones, 25);
+          expect(Note.a.inOctave(2).semitones, 34);
+          expect(Note.c.inOctave(3).semitones, 37);
+          expect(Note.a.inOctave(4).semitones, 58);
         },
       );
     });
@@ -52,20 +52,21 @@ void main() {
           expect(Note.c.inOctave(4).difference(Note.c.inOctave(4)), 0);
           expect(
             const Note(Notes.e, Accidental.sharp)
+                .inOctave(4)
                 .difference(Note.f.inOctave(4)),
             0,
           );
           expect(Note.c.inOctave(4).difference(Note.dFlat.inOctave(4)), 1);
           expect(Note.c.inOctave(4).difference(Note.cSharp.inOctave(4)), 1);
           expect(
-            Note.b.inOctave(4).difference(Note.c.inOctave(4).inOctave(5)),
+            Note.b.inOctave(4).difference(Note.c.inOctave(5)),
             1,
           );
           expect(Note.f.inOctave(4).difference(Note.g.inOctave(4)), 2);
           expect(Note.f.inOctave(4).difference(Note.aFlat.inOctave(4)), 3);
           expect(Note.e.inOctave(4).difference(Note.aFlat.inOctave(4)), 4);
           expect(
-            Note.a.inOctave(4).difference(Note.d.inOctave(4).inOctave(5)),
+            Note.a.inOctave(4).difference(Note.d.inOctave(5)),
             5,
           );
           expect(Note.d.inOctave(4).difference(Note.aFlat.inOctave(4)), 6);