feat: slash chord support (G/B parses+transposes bass note)

crates/domain/src/services/transposer.rs

@@ -15,9 +15,14 @@ pub enum TransposeError {
 impl ChordTransposer {
     pub fn transpose_chord(&self, chord: &Chord, semitones: i8) -> Chord {
         let new_semitone = (chord.root.semitone() as i16 + semitones as i16).rem_euclid(12) as u8;
+        let bass = chord.bass.map(|b| {
+            let s = (b.semitone() as i16 + semitones as i16).rem_euclid(12) as u8;
+            Note::from_semitone(s)
+        });
         Chord {
             root: Note::from_semitone(new_semitone),
             descriptor: chord.descriptor.clone(),
+            bass,
         }
     }
 

crates/domain/src/tests/chord.rs

@@ -5,6 +5,7 @@ fn parse_simple() {
     let c = Chord::parse("Em").unwrap();
     assert_eq!(c.root, crate::value_objects::Note::E);
     assert_eq!(c.descriptor.as_deref(), Some("m"));
+    assert!(c.bass.is_none());
 }
 
 #[test]
@@ -12,6 +13,7 @@ fn parse_no_descriptor() {
     let c = Chord::parse("G").unwrap();
     assert_eq!(c.root, crate::value_objects::Note::G);
     assert!(c.descriptor.is_none());
+    assert!(c.bass.is_none());
 }
 
 #[test]
@@ -26,6 +28,7 @@ fn name_sharp() {
     let c = Chord {
         root: crate::value_objects::Note::FSharpGFlat,
         descriptor: Some("m".into()),
+        bass: None,
     };
     assert_eq!(c.name(true), "F#m");
 }
@@ -35,6 +38,7 @@ fn name_flat() {
     let c = Chord {
         root: crate::value_objects::Note::ASharpBFlat,
         descriptor: None,
+        bass: None,
     };
     assert_eq!(c.name(false), "Bb");
 }
@@ -45,3 +49,39 @@ fn parse_flat_with_descriptor() {
     assert_eq!(c.root, crate::value_objects::Note::ASharpBFlat);
     assert_eq!(c.descriptor.as_deref(), Some("m"));
 }
+
+#[test]
+fn parse_slash_chord() {
+    let c = Chord::parse("G/B").unwrap();
+    assert_eq!(c.root, crate::value_objects::Note::G);
+    assert!(c.descriptor.is_none());
+    assert_eq!(c.bass, Some(crate::value_objects::Note::B));
+}
+
+#[test]
+fn parse_slash_chord_with_descriptor() {
+    let c = Chord::parse("Am7/G").unwrap();
+    assert_eq!(c.root, crate::value_objects::Note::A);
+    assert_eq!(c.descriptor.as_deref(), Some("m7"));
+    assert_eq!(c.bass, Some(crate::value_objects::Note::G));
+}
+
+#[test]
+fn parse_slash_chord_with_sharp_bass() {
+    let c = Chord::parse("D/F#").unwrap();
+    assert_eq!(c.root, crate::value_objects::Note::D);
+    assert_eq!(c.bass, Some(crate::value_objects::Note::FSharpGFlat));
+}
+
+#[test]
+fn name_slash_chord() {
+    let c = Chord::parse("G/B").unwrap();
+    assert_eq!(c.name(true), "G/B");
+}
+
+#[test]
+fn name_slash_chord_transpose_display() {
+    let c = Chord::parse("D/F#").unwrap();
+    assert_eq!(c.name(true), "D/F#");
+    assert_eq!(c.name(false), "D/Gb");
+}

crates/domain/src/tests/song.rs

@@ -11,6 +11,7 @@ fn lyric_line_chord_positions() {
                 chord: Chord {
                     root: Note::E,
                     descriptor: Some("m".into()),
+                    bass: None,
                 },
             },
             ChordPosition {
@@ -18,6 +19,7 @@ fn lyric_line_chord_positions() {
                 chord: Chord {
                     root: Note::C,
                     descriptor: None,
+                    bass: None,
                 },
             },
         ],

crates/domain/src/tests/transposer.rs

@@ -66,3 +66,17 @@ fn transpose_to_key() {
     let result = t.transpose_to_key(&song, "A").unwrap();
     assert_eq!(result.sections.len(), 0);
 }
+
+#[test]
+fn transpose_slash_chord() {
+    let t = ChordTransposer;
+    let result = t.transpose_chord(&chord("G/B"), 2);
+    assert_eq!(result.name(true), "A/C#");
+}
+
+#[test]
+fn transpose_slash_chord_down() {
+    let t = ChordTransposer;
+    let result = t.transpose_chord(&chord("D/F#"), -2);
+    assert_eq!(result.name(true), "C/E");
+}

crates/domain/src/value_objects/chord.rs

@@ -6,17 +6,33 @@ use serde::{Deserialize, Serialize};
 pub struct Chord {
     pub root: Note,
     pub descriptor: Option<String>,
+    pub bass: Option<Note>,
 }
 
 impl Chord {
     pub fn parse(s: &str) -> Option<Self> {
-        let (root, consumed) = Note::parse_prefix(s)?;
-        let descriptor = if consumed < s.len() {
-            Some(s[consumed..].to_string())
+        let (main, bass_str) = match s.rsplit_once('/') {
+            Some((m, b)) if !b.is_empty() => (m, Some(b)),
+            _ => (s, None),
+        };
+
+        let (root, consumed) = Note::parse_prefix(main)?;
+        let descriptor = if consumed < main.len() {
+            Some(main[consumed..].to_string())
         } else {
             None
         };
-        Some(Chord { root, descriptor })
+
+        let bass = match bass_str {
+            Some(b) => Some(Note::parse(b)?),
+            None => None,
+        };
+
+        Some(Chord {
+            root,
+            descriptor,
+            bass,
+        })
     }
 
     pub fn name(&self, use_sharps: bool) -> String {
@@ -25,9 +41,20 @@ impl Chord {
         } else {
             self.root.to_flat_str()
         };
-        match &self.descriptor {
+        let base = match &self.descriptor {
             Some(d) => format!("{}{}", root_str, d),
             None => root_str.to_string(),
+        };
+        match &self.bass {
+            Some(b) => {
+                let bass_str = if use_sharps {
+                    b.to_sharp_str()
+                } else {
+                    b.to_flat_str()
+                };
+                format!("{}/{}", base, bass_str)
+            }
+            None => base,
         }
     }
 }