feat(interval): add descending method (#103)

* feat(interval): add `descending` method * refactor(tonality): use `Interval.descending` method
albertms10 · May 9, 2023 · 429f904 · 429f904
1 parent c4db414
commit 429f904
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Showing 4 changed files with 54 additions and 8 deletions.
diff --git a/lib/src/interval/interval.dart b/lib/src/interval/interval.dart
@@ -148,6 +148,19 @@ class Interval implements MusicItem {
   /// ```
   bool get isDescending => size.isNegative;
 
+  /// Returns a copy of this [Interval] based on [isDescending].
+  ///
+  /// Example:
+  /// ```dart
+  /// Interval.minorSecond.descending() == -Interval.minorSecond
+  /// Interval.majorThird.descending(isDescending: false) == Interval.majorThird
+  /// (-Interval.perfectFifth).descending() == -Interval.perfectFifth
+  /// (-Interval.majorSeventh).descending(isDescending: false)
+  ///   == Interval.majorSeventh
+  /// ```
+  Interval descending({bool isDescending = true}) =>
+      this.isDescending != isDescending ? -this : Interval._(size, quality);
+
   /// Returns the inverted of this [Interval].
   ///
   /// Example:

diff --git a/lib/src/tonality/key_signature.dart b/lib/src/tonality/key_signature.dart
@@ -47,10 +47,8 @@ class KeySignature implements Comparable<KeySignature> {
   /// const KeySignature(2, Accidental.sharp).majorNote == Note.d
   /// ```
   Note get majorNote {
-    final fifthInterval = Interval.perfect(
-      5 * (accidental == Accidental.flat ? -1 : 1),
-      PerfectQuality.perfect,
-    );
+    final fifthInterval = Interval.perfectFifth
+        .descending(isDescending: accidental == Accidental.flat);
 
     return EnharmonicNote(
       (fifthInterval.semitones * accidentals + 1).chromaticModExcludeZero,

diff --git a/lib/src/tonality/tonality.dart b/lib/src/tonality/tonality.dart
@@ -68,10 +68,7 @@ class Tonality implements Comparable<Tonality> {
   /// ```
   Tonality get relative => Tonality(
         note.transposeBy(
-          Interval.imperfect(
-            3 * (mode == TonalMode.major ? -1 : 1),
-            ImperfectQuality.minor,
-          ),
+          Interval.minorThird.descending(isDescending: mode == TonalMode.major),
         ),
         mode.opposite,
       );

diff --git a/test/src/interval/interval_test.dart b/test/src/interval/interval_test.dart
@@ -163,6 +163,44 @@ void main() {
       });
     });
 
+    group('.descending()', () {
+      test(
+        'should return the descending Interval based on isDescending',
+        () {
+          expect(Interval.majorSecond.descending(), -Interval.majorSecond);
+          expect(
+            Interval.minorThird.descending(isDescending: false),
+            Interval.minorThird,
+          );
+          expect(
+            (-Interval.minorSixth).descending(isDescending: false),
+            Interval.minorSixth,
+          );
+          expect(
+            (-Interval.perfectOctave).descending(),
+            -Interval.perfectOctave,
+          );
+        },
+      );
+
+      test(
+        'should return a copy of this Interval based on isDescending',
+        () {
+          const ascendingInterval = Interval.perfectFourth;
+          expect(
+            identical(ascendingInterval.descending(), ascendingInterval),
+            isFalse,
+          );
+
+          final descendingInterval = -Interval.minorThird;
+          expect(
+            identical(descendingInterval.descending(), descendingInterval),
+            isFalse,
+          );
+        },
+      );
+    });
+
     group('.inverted', () {
       test('should return the inverted of this Interval', () {
         expect(Interval.diminishedUnison.inverted, Interval.augmentedOctave);