✨ feat(interval): take distance sign into account in circleFrom (#…

…199)

* ✨ feat(interval): take distance sign into account in `circleFrom`

* ✅ test(interval): add more test cases for `circleFrom`

lib/src/interval/interval.dart

@@ -256,18 +256,21 @@ final class Interval implements Comparable<Interval> {
   ///
   /// Interval.P4.circleFrom(Note.c, distance: 5)
   ///   == [Note.c, Note.f, Note.b.flat, Note.e.flat, Note.a.flat, Note.d.flat]
+  ///
+  /// Interval.P4.circleFrom(Note.c, distance: -3)
+  ///   == Interval.P5.circleFrom(Note.c, distance: 3)
   /// ```
   List<T> circleFrom<T extends Scalable<T>>(
     T scalable, {
     required int distance,
   }) =>
-      distance == 0
-          ? [scalable]
-          : List.filled(distance.abs(), null).fold(
-              [scalable],
-              (circleItems, _) =>
-                  [...circleItems, circleItems.last.transposeBy(this)],
-            );
+      List.filled(distance.abs(), null).fold(
+        [scalable],
+        (circleItems, _) => [
+          ...circleItems,
+          circleItems.last.transposeBy(distance.isNegative ? -this : this),
+        ],
+      );
 
   /// Adds [other] to this [Interval].
   ///

lib/src/note/note.dart

@@ -230,10 +230,8 @@ final class Note implements Comparable<Note>, Scalable<Note> {
       (
         sharps:
             Interval.P5.circleFrom(this, distance: distance).skip(1).toList(),
-        flats: (-Interval.P5)
-            .circleFrom(this, distance: distance)
-            .skip(1)
-            .toList(),
+        flats:
+            Interval.P5.circleFrom(this, distance: -distance).skip(1).toList(),
       );
 
   /// Returns the flattened version of [circleOfFifths] from this [Note] up to
@@ -277,12 +275,13 @@ final class Note implements Comparable<Note>, Scalable<Note> {
   int get circleOfFifthsDistance =>
       Tonality(this, TonalMode.major).keySignature.distance;
 
-  /// Returns the exact fifths distance between this [Note] and [other].
+  /// Returns the fifths distance between this [Note] and [other].
   ///
   /// Example:
   /// ```dart
+  /// Note.c.fifthsDistanceWith(Note.e.flat) == -3
+  /// Note.f.sharp.fifthsDistanceWith(Note.b) == -1
   /// Note.a.flat.fifthsDistanceWith(Note.c.sharp) == 11
-  /// Note.a.flat.fifthsDistanceWith(Note.d.flat) == -1
   /// ```
   int fifthsDistanceWith(Note other) =>
       Interval.P5.distanceBetween(this, other);

lib/src/tonality/key_signature.dart

@@ -13,11 +13,12 @@ final class KeySignature implements Comparable<KeySignature> {
   factory KeySignature.fromDistance(int distance) {
     if (distance == 0) return empty;
 
-    final interval = distance.isNegative ? Interval.P4 : Interval.P5;
-    final startingNote = distance.isNegative ? Note.b.flat : Note.f.sharp;
+    final firstAccidentalNote =
+        distance.isNegative ? Note.b.flat : Note.f.sharp;
 
     return KeySignature(
-      interval.circleFrom(startingNote, distance: distance.incrementBy(-1)),
+      Interval.P5
+          .circleFrom(firstAccidentalNote, distance: distance.incrementBy(-1)),
     );
   }
 
@@ -70,8 +71,7 @@ final class KeySignature implements Comparable<KeySignature> {
   /// )
   /// ```
   ({Tonality major, Tonality minor}) get tonalities {
-    final interval = distance.isNegative ? Interval.P4 : Interval.P5;
-    final rootNote = interval.circleFrom(Note.c, distance: distance).last;
+    final rootNote = Interval.P5.circleFrom(Note.c, distance: distance).last;
 
     return (
       major: rootNote.major,

test/src/interval/interval_test.dart

@@ -384,6 +384,11 @@ void main() {
             Note.a.flat.flat,
           ],
         );
+
+        expect(
+          Interval.P4.circleFrom(Note.c, distance: -7),
+          Interval.P5.circleFrom(Note.c, distance: 7),
+        );
       });
     });