feat: simplify chord guide feature; updated help doc; added hotkeys doc

src/components/piano-roll/chordGuideUtil.ts

@@ -0,0 +1,42 @@
+import type { KeySignature, KGProject } from '../../core/KGProject';
+import { getEffectiveKeySignatureAtBeat } from '../../util/globalTrackUtil';
+import { getChordGuideModeFromKeySignature } from '../../util/scaleUtil';
+
+export type ChordGuideFunction = 'N' | 'T' | 'S' | 'D';
+export type ChordGuideMode = 'ionian' | 'aeolian';
+
+export function getNextChordGuideSelection(current: ChordGuideFunction): ChordGuideFunction {
+  switch (current) {
+    case 'N':
+      return 'T';
+    case 'T':
+      return 'S';
+    case 'S':
+      return 'D';
+    default:
+      return 'N';
+  }
+}
+
+export function getNextChordCandidateIndex(
+  currentIndex: number,
+  candidateCount: number,
+  direction: 1 | -1
+): number {
+  if (candidateCount <= 1) {
+    return currentIndex;
+  }
+
+  return (currentIndex + direction + candidateCount) % candidateCount;
+}
+
+export function resolveChordGuideContext(project: KGProject, beat: number): {
+  keySignature: KeySignature;
+  mode: ChordGuideMode;
+} {
+  const keySignature = getEffectiveKeySignatureAtBeat(project, beat);
+  return {
+    keySignature,
+    mode: getChordGuideModeFromKeySignature(keySignature),
+  };
+}