add note

src/note.rs

@@ -0,0 +1,63 @@
+use core::fmt;
+use std::fmt::Formatter;
+
+#[derive(Clone, Debug, PartialEq)]
+pub enum RelativeNote {
+    C,
+    CSharp,
+    D,
+    DSharp,
+    E,
+    F,
+    FSharp,
+    G,
+    GSharp,
+    A,
+    ASharp,
+    B,
+}
+
+#[derive(Clone, Debug, PartialEq)]
+pub struct Note {
+    relative: RelativeNote,
+    octave: u8, // upper limit? 8?
+}
+
+impl fmt::Display for Note {
+    fn fmt(&self, f: &mut Formatter<'_>) -> fmt::Result {
+        write!(
+            f,
+            "{}{}",
+            match self.relative {
+                 RelativeNote::C      => "C",
+                 RelativeNote::CSharp => "C#",
+                 RelativeNote::D      => "D",
+                 RelativeNote::DSharp => "D#",
+                 RelativeNote::E      => "E",
+                 RelativeNote::F      => "F",
+                 RelativeNote::FSharp => "F#",
+                 RelativeNote::G      => "G",
+                 RelativeNote::GSharp => "G#",
+                 RelativeNote::A      => "A",
+                 RelativeNote::ASharp => "A#",
+                 RelativeNote::B      => "B",
+            },
+            self.octave
+        )
+    }
+}
+
+#[cfg(test)]
+mod test {
+    use crate::note::{Note, RelativeNote};
+
+    #[test]
+    fn c4() {
+        assert_eq!(Note { relative: RelativeNote::C, octave: 4 }.to_string(), "C4");
+    }
+
+    #[test]
+    fn a_sharp_0() {
+        assert_eq!(Note { relative: RelativeNote::ASharp, octave: 0 }.to_string(), "A#0");
+    }
+}