Supported flats in chord progressions to parse

melanchall · Dec 24, 2023 · 16c1e1a · 16c1e1a
1 parent 0aa80dd
commit 16c1e1a
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Showing 2 changed files with 13 additions and 2 deletions.
diff --git a/DryWetMidi.Tests/MusicTheory/ChordProgression/ChordProgressionTests.cs b/DryWetMidi.Tests/MusicTheory/ChordProgression/ChordProgressionTests.cs
@@ -12,6 +12,7 @@ public sealed class ChordProgressionTests
         [TestCase("I-II-IV", "C major", new[] { "C", "D", "F" })]
         [TestCase("I-II-iv", "C major", new[] { "C", "D", "F" })]
         [TestCase("Im-ii7-v", "C major", new[] { "Cm", "D7", "G" })]
+        [TestCase("i - bVI - III - bVII", "C major", new[] { "C", "G#", "E", "A#" })]
         public void Parse(string input, string scaleString, string[] expectedChords)
         {
             var chordProgression = ChordProgression.Parse(input, Scale.Parse(scaleString));

diff --git a/DryWetMidi/MusicTheory/ChordProgression/ChordProgressionParser.cs b/DryWetMidi/MusicTheory/ChordProgression/ChordProgressionParser.cs
@@ -10,12 +10,14 @@ internal static class ChordProgressionParser
         private const char PartsDelimiter = '-';
 
         private const string ScaleDegreeGroupName = "sd";
+        private const string AccidentalGroupName = "ac";
 
+        private static readonly string AccidentalGroup = $"(?<{AccidentalGroupName}>b)";
         private static readonly string ScaleDegreeGroup = $"(?<{ScaleDegreeGroupName}>(?i:M{{0,4}}(CM|CD|D?C{{0,3}})(XC|XL|L?X{{0,3}})(IX|IV|V?I{{0,3}})))";
 
         private static readonly string[] Patterns = new[]
         {
-            $@"{ScaleDegreeGroup}\s*{ChordParser.ChordCharacteristicsGroup}"
+            $@"{AccidentalGroup}?\s*{ScaleDegreeGroup}\s*{ChordParser.ChordCharacteristicsGroup}"
         };
 
         private static readonly Dictionary<char, int> RomanMap = new Dictionary<char, int>
@@ -57,11 +59,19 @@ internal static ParsingResult TryParse(string input, Scale scale, out ChordProgr
                 var degree = RomanToInteger(degreeRoman);
                 var rootNoteName = scale.GetStep(degree - 1);
 
+                var accidentalGroup = match.Groups[AccidentalGroupName];
+                if (accidentalGroup.Success)
+                {
+                    var accidental = accidentalGroup.Value;
+                    if (accidental == "b")
+                        rootNoteName = (NoteName)(((int)rootNoteName + Octave.OctaveSize - 1) % Octave.OctaveSize);
+                }
+
                 var fullString = match.Value;
                 var matchIndex = match.Index;
                 var degreeGroupIndex = degreeGroup.Index;
                 var chordString =
-                    fullString.Substring(0, degreeGroupIndex - matchIndex) +
+                    fullString.Substring(0, degreeGroupIndex - matchIndex - (accidentalGroup.Success ? accidentalGroup.Length : 0)) +
                     rootNoteName +
                     fullString.Substring(degreeGroupIndex - matchIndex + degreeGroup.Length);