Note.enharmonic calculates octaves of an equivalent pitch class (#225)

packages/note/README.md

@@ -130,12 +130,15 @@ Note.transposeFifths("G", 3); // => "E"
 
 #### `Note.distance(from: string, to: string) => string`
 
-Find interval between notes:
+Find the interval between two notes:
 
 ```js
+Note.distance("C", "D").toEqual("2M");
+Note.distance("C3", "E3").toEqual("3M");
+Note.distance("C3", "E4").toEqual("10M");
 ```
 
-### Names collections
+### Named collections
 
 #### `names(array?: any[]) => string[]`
 
@@ -185,12 +188,26 @@ Note.simplify("C##"); // => "D"
 Note.simplify("C###"); // => "D#"
 ```
 
-#### `enharmonic(noteName: string) => string`
+#### `enharmonic(noteName: string, pitchClass?: string) => string`
 
-Given a note name, returns it enharmonic not (or "" if not valid note):
+Given a note name, returns its enharmonic (or "" if not valid note):
 
 ```js
 Note.enharmonic("C#"); // => "Db"
 Note.enharmonic("C##"); // => "D"
 Note.enharmonic("C###"); // => "Eb"
 ```
+
+The destination pitch class can be enforced to calculate the octave:
+
+```js
+Note.enharmonic("F2", "E#"); // => "E#2"
+Note.enharmonic("B2", "Cb"); // => "Cb3"
+Note.enharmonic("C2", "B#"); // => "B#1"
+```
+
+Enforced pitch class must have the same chroma as the note, otherwise "" is returned:
+
+```js
+Note.enharmonic("F2", "Eb"); // => ""
+```

packages/note/index.ts

@@ -216,30 +216,65 @@ export function sortedUniqNames(notes: any[]): string[] {
  * simplify("C###")
  * simplify("B#4") // => "C5"
  */
-export const simplify = nameBuilder(true);
-
+export const simplify = (noteName: NoteName | Pitch): string => {
+  const note = get(noteName);
+  if (note.empty) {
+    return "";
+  }
+  return midiToNoteName(note.midi || note.chroma, {
+    sharps: note.alt > 0,
+    pitchClass: note.midi === null,
+  });
+};
 /**
  * Get enharmonic of a note
  *
  * @function
  * @param {string} note
- * @return {string} the enharmonic note or '' if not valid note
+ * @param [string] - [optional] Destination pitch class
+ * @return {string} the enharmonic note name or '' if not valid note
  * @example
  * Note.enharmonic("Db") // => "C#"
  * Note.enharmonic("C") // => "C"
+ * Note.enharmonic("F2","E#") // => "E#2"
  */
-export const enharmonic = nameBuilder(false);
+export function enharmonic(noteName: string, destName?: string) {
+  const src = get(noteName);
+  if (src.empty) {
+    return "";
+  }
+
+  // destination: use given or generate one
+  const dest = get(
+    destName ||
+      midiToNoteName(src.midi || src.chroma, {
+        sharps: src.alt < 0,
+        pitchClass: true,
+      })
+  );
+
+  // ensure destination is valid
+  if (dest.empty || dest.chroma !== src.chroma) {
+    return "";
+  }
+
+  // if src has no octave, no need to calculate anything else
+  if (src.oct === undefined) {
+    return dest.pc;
+  }
 
-function nameBuilder(sameAccidentals: boolean) {
-  return (noteName: NoteName | Pitch): string => {
-    const note = get(noteName);
-    if (note.empty) {
-      return "";
-    }
-    const sharps = sameAccidentals ? note.alt > 0 : note.alt < 0;
-    const pitchClass = note.midi === null;
-    return midiToNoteName(note.midi || note.chroma, { sharps, pitchClass });
-  };
+  // detect any octave overflow
+  const srcChroma = src.chroma - src.alt;
+  const destChroma = dest.chroma - dest.alt;
+  const destOctOffset =
+    srcChroma > 11 || destChroma < 0
+      ? -1
+      : srcChroma < 0 || destChroma > 11
+      ? +1
+      : 0;
+  // calculate the new octave
+  const destOct = src.oct + destOctOffset;
+  return dest.pc + destOct;
 }
 
 export default {

packages/note/test.ts

@@ -98,8 +98,14 @@ describe("note", () => {
     expect(Note.enharmonic("C###")).toEqual("Eb");
     expect(Note.enharmonic("B#4")).toEqual("C5");
     const notes = $("C## C### F##4 Gbbb5 B#4 Cbb4");
-    expect(notes.map(Note.enharmonic)).toEqual($("D Eb G4 E5 C5 A#3"));
+    expect(notes.map((n) => Note.enharmonic(n))).toEqual(
+      $("D Eb G4 E5 C5 A#3")
+    );
     expect(Note.enharmonic("x")).toEqual("");
+    expect(Note.enharmonic("F2", "E#")).toBe("E#2");
+    expect(Note.enharmonic("B2", "Cb")).toBe("Cb3");
+    expect(Note.enharmonic("C2", "B#")).toBe("B#1");
+    expect(Note.enharmonic("F2", "Eb")).toBe("");
   });
 
   test("transposeFifths", () => {