feat(mixed_num): 🔥 drop support for negative values

Signed-off-by: Albert Mañosa <26429103+albertms10@users.noreply.github.com>

lib/src/utils/mixed_num.dart

@@ -1,5 +1,4 @@
 import 'package:meta/meta.dart' show immutable;
-import 'package:music_notes/utils.dart';
 
 /// A mixed number representation.
 @immutable
@@ -16,6 +15,10 @@ final class MixedNum implements Comparable<MixedNum> {
   /// Creates a new [MixedNum] from [integer], [numerator], and [denominator].
   const MixedNum(this.integer, [this.numerator = 0, this.denominator = 1])
       : assert(
+          integer >= 0,
+          'The whole part must be greater or equal than zero.',
+        ),
+        assert(
           numerator >= 0,
           'The denominator must be greater or equal than zero.',
         ),
@@ -47,6 +50,9 @@ final class MixedNum implements Comparable<MixedNum> {
 
   /// Creates a new [MixedNum] from [number] and [tolerance].
   factory MixedNum.fromDouble(double number, {int tolerance = 100}) {
+    assert(!number.isNegative, 'Number must be positive.');
+    assert(!tolerance.isNegative, 'Tolerance must be positive.');
+
     final wholePart = number.floor();
     final fracPart = number - wholePart;
 
@@ -56,13 +62,13 @@ final class MixedNum implements Comparable<MixedNum> {
     var bestDenominator = 1;
     var bestError = double.infinity;
 
-    for (var den = 1; den <= tolerance; ++den) {
-      final num = (fracPart * den).round();
-      final error = (fracPart - num / den).abs();
+    for (var denominator = 1; denominator <= tolerance; ++denominator) {
+      final numerator = (fracPart * denominator).round();
+      final error = (fracPart - numerator / denominator).abs();
       if (error < bestError) {
         bestError = error;
-        bestNumerator = num;
-        bestDenominator = den;
+        bestNumerator = numerator;
+        bestDenominator = denominator;
         gcdValue = bestNumerator.gcd(bestDenominator);
       }
       if (error == 0) break;
@@ -82,7 +88,7 @@ final class MixedNum implements Comparable<MixedNum> {
   MixedNum get simple => MixedNum.fromDouble(toDouble());
 
   /// This [MixedNum] as a [double].
-  double toDouble() => integer + _fractionPart * integer.nonZeroSign;
+  double toDouble() => integer + _fractionPart;
 
   double get _fractionPart => numerator / denominator;
 

test/utils/mixed_num_test.dart

@@ -9,6 +9,7 @@ void main() {
       test('throws an assertion error when arguments are incorrect', () {
         expect(() => MixedNum(1, -2), throwsA(isA<AssertionError>()));
         expect(() => MixedNum(1, 1, 0), throwsA(isA<AssertionError>()));
+        expect(() => MixedNum(-1), throwsA(isA<AssertionError>()));
       });
     });
 
@@ -29,7 +30,6 @@ void main() {
         expect(MixedNum.parse('5  3/5'), const MixedNum(5, 3, 5));
         expect(MixedNum.parse('4 5/4'), const MixedNum(4, 5, 4));
         expect(MixedNum.parse('32 10/111'), const MixedNum(32, 10, 111));
-        expect(MixedNum.parse('-4 3/4'), const MixedNum(-4, 3, 4));
       });
     });
 
@@ -47,14 +47,21 @@ void main() {
         );
         expect(MixedNum.fromDouble(1.375), const MixedNum(1, 3, 8));
       });
+
+      test('throws an assertion error when arguments are incorrect', () {
+        expect(() => MixedNum.fromDouble(-1), throwsA(isA<AssertionError>()));
+        expect(
+          () => MixedNum.fromDouble(1, tolerance: -1),
+          throwsA(isA<AssertionError>()),
+        );
+      });
     });
 
     group('.simple', () {
       test('returns the simplified version of this MixedNum', () {
         expect(const MixedNum(0, 1, 3).simple, const MixedNum(0, 1, 3));
         expect(const MixedNum(2).simple, const MixedNum(2));
         expect(const MixedNum(3, 1).simple, const MixedNum(4));
-        expect(const MixedNum(-3, 5, 5).simple, const MixedNum(-4));
         expect(const MixedNum(1, 5, 2).simple, const MixedNum(3, 1, 2));
       });
     });
@@ -74,7 +81,6 @@ void main() {
         expect(const MixedNum(0).toString(), '0');
         expect(const MixedNum(3).toString(), '3');
         expect(const MixedNum(0, 1, 3).toString(), '1/3');
-        expect(const MixedNum(-12, 3, 8).toString(), '-12 3/8');
         expect(const MixedNum(3, 5, 4).toString(), '3 5/4');
       });
     });
@@ -83,13 +89,11 @@ void main() {
       test('sorts MixedNums in a collection', () {
         final orderedSet = SplayTreeSet<MixedNum>.of({
           const MixedNum(0),
-          const MixedNum(-3, 1, 2),
           const MixedNum(1, 2, 2),
           const MixedNum(0, 7, 2),
           const MixedNum(0, 1, 9),
         });
         expect(orderedSet.toList(), const [
-          MixedNum(-3, 1, 2),
           MixedNum(0),
           MixedNum(0, 1, 9),
           MixedNum(1, 2, 2),