Reworking chord detection to be order independent.

Resolves tonaljs#160.

docs/CONTRIBUTING.md

@@ -32,7 +32,7 @@ If you are adding new functionality or fixing a bug, please add a test for it.
 yarn test:ci
 ```
 
-#### How to add a new module
+### How to add a new module
 
 To create a new module:
 

packages/chord-detect/index.ts

@@ -1,5 +1,7 @@
 import { all } from "@tonaljs/chord-type";
-import { note } from "@tonaljs/core";
+import { note, distance } from "@tonaljs/core";
+import { name, sortedNames } from "@tonaljs/note";
+import { simplify } from "@tonaljs/interval";
 import { modes } from "@tonaljs/pcset";
 
 interface FoundChord {
@@ -20,7 +22,9 @@ const namedSet = (notes: string[]) => {
 };
 
 export function detect(source: string[]): string[] {
-  const notes = source.map((n) => note(n).pc).filter((x) => x);
+  const notes = sortedNames(source)
+    .map((n) => note(n).pc)
+    .filter((x) => x);
   if (note.length === 0) {
     return [];
   }
@@ -33,12 +37,41 @@ export function detect(source: string[]): string[] {
     .map((chord) => chord.name);
 }
 
+// Assumes that chord is presorted
+function findRoot(chord: string[]): string {
+  let foundRoot = null;
+  chord.every((note) => {
+    const workComplete = chord.some((otherNote) => {
+      const interval = simplify(distance(note, otherNote));
+      const orderedNotes = sortedNames([note, otherNote]);
+      if (interval === "5P") {
+        foundRoot = orderedNotes[0];
+        return foundRoot; // Loop is complete
+      } else if (interval === "4P") {
+        foundRoot = orderedNotes[1];
+        return foundRoot; // Loop is complete
+      }
+      return false; // continue looping
+    });
+    // Continue looping if the root note was not found
+    return !workComplete;
+  });
+  if (foundRoot) {
+    return foundRoot;
+  } else {
+    // Defaults to the old behavior if the chord is complex and the root note cannot be easily found
+    return chord[0];
+  }
+}
+
+// assumes that notes is presorted
 function findExactMatches(notes: string[], weight: number): FoundChord[] {
-  const tonic = notes[0];
-  const tonicChroma = note(tonic).chroma;
+  const root = findRoot(notes);
   const noteName = namedSet(notes);
-  // we need to test all chormas to get the correct baseNote
+  // we need to test all chromas to get the correct baseNote
   const allModes = modes(notes, false);
+  const baseNote = notes[0];
+  const baseChroma = note(baseNote).chroma;
 
   const found: FoundChord[] = [];
   allModes.forEach((mode, index) => {
@@ -47,15 +80,16 @@ function findExactMatches(notes: string[], weight: number): FoundChord[] {
 
     chordTypes.forEach((chordType) => {
       const chordName = chordType.aliases[0];
-      const baseNote = noteName(index);
-      const isInversion = index !== tonicChroma;
+      const rootNote = noteName(index);
+      const isInversion = note(rootNote).chroma !== baseChroma;
+
       if (isInversion) {
         found.push({
           weight: 0.5 * weight,
-          name: `${baseNote}${chordName}/${tonic}`,
+          name: `${rootNote}${chordName}/${baseNote}`,
         });
       } else {
-        found.push({ weight: 1 * weight, name: `${baseNote}${chordName}` });
+        found.push({ weight: 1 * weight, name: `${root}${chordName}` });
       }
     });
   });

packages/chord-detect/package.json

@@ -17,6 +17,8 @@
   "dependencies": {
     "@tonaljs/chord-type": "^3.6.0",
     "@tonaljs/core": "^3.5.4",
+    "@tonaljs/interval": "^3.5.4",
+    "@tonaljs/note": "^3.5.4",
     "@tonaljs/pcset": "^3.5.4"
   },
   "author": "[email protected]",

packages/chord-detect/test.ts

@@ -2,14 +2,20 @@ import { detect } from "./index";
 
 describe("@tonal/chord-detect", () => {
   test("detect", () => {
-    expect(detect(["D", "F#", "A", "C"])).toEqual(["D7"]);
-    expect(detect(["F#", "A", "C", "D"])).toEqual(["D7/F#"]);
-    expect(detect(["A", "C", "D", "F#"])).toEqual(["D7/A"]);
-    expect(detect(["E", "G#", "B", "C#"])).toEqual(["E6", "C#m7/E"]);
+    expect(detect(["D", "F#", "A", "C"])).toEqual(["D7/C"]);
+    expect(detect(["D3", "F#4", "A3", "C4"])).toEqual(["D7"]);
+    expect(detect(["F#4", "A3", "C4", "D3"])).toEqual(["D7"]);
+    expect(detect(["F#2", "A3", "C4", "D3"])).toEqual(["D7/F#"]);
+    expect(detect(["A3", "C4", "D3", "F#4"])).toEqual(["D7"]);
+    expect(detect(["A2", "C4", "D3", "F#4"])).toEqual(["D7/A"]);
+    expect(detect(["E3", "G#4", "B4", "C#4"])).toEqual(["E6", "C#m7/E"]);
+    expect(detect(["C4", "E4", "G4"])).toEqual(["CM", "Em#5/C"]);
+    expect(detect(["E4", "G4", "C5"])).toEqual(["Gm#5", "CM/E"]);
   });
 
   test("(regression) detect aug", () => {
     expect(detect(["C", "E", "G#"])).toEqual(["Caug", "Eaug/C", "G#aug/C"]);
+    expect(detect(["E", "G#", "C"])).toEqual(["Caug", "Eaug/C", "G#aug/C"]);
   });
 
   test("edge cases", () => {