feat: implemented the logic to automatically create a chord when a suitable guide chord is highlighted.

src/components/piano-roll/PianoGrid.tsx

@@ -167,6 +167,18 @@ const PianoGrid: React.FC<PianoGridProps> = ({
     return highlights;
   }, [cursorPosition, matchingChords, selectedChordIndex]);
 
+  const cursorPitch = cursorPosition?.pitch ?? null;
+
+  useEffect(() => {
+    const pianoRollState = KGPianoRollState.instance();
+    pianoRollState.setCurrentMatchingChords(matchingChords);
+    pianoRollState.setCurrentChordCursorPitch(cursorPitch);
+  }, [matchingChords, cursorPitch]);
+
+  useEffect(() => {
+    KGPianoRollState.instance().setCurrentSelectedChordIndex(selectedChordIndex);
+  }, [selectedChordIndex]);
+
   const lastEditedNoteLength = KGPianoRollState.instance().getLastEditedNoteLength();
 
   // Reset selected chord index when cursor moves to a different pitch or beat

src/core/state/KGPianoRollState.ts

@@ -17,6 +17,9 @@ export class KGPianoRollState {
   // Chord guide state
   private currentSuitableChords: Record<string, string[]> = {}; // Map of chord symbols to note names (e.g., {"I": ["C", "E", "G"]})
   private currentSuitableChordsPitchClasses: Record<string, number[]> = {}; // Map of chord symbols to pitch classes (e.g., {"I": [0, 4, 7]})
+  private currentMatchingChords: number[][] = [];
+  private currentSelectedChordIndex: number = 0;
+  private currentChordCursorPitch: number | null = null;
 
   private constructor() {
     console.log("KGPianoRollState initialized");
@@ -77,4 +80,28 @@ export class KGPianoRollState {
   public setCurrentSuitableChordsPitchClasses(chordsPitchClasses: Record<string, number[]>): void {
     this.currentSuitableChordsPitchClasses = chordsPitchClasses;
   }
+
+  public getCurrentMatchingChords(): number[][] {
+    return this.currentMatchingChords;
+  }
+
+  public setCurrentMatchingChords(chords: number[][]): void {
+    this.currentMatchingChords = chords;
+  }
+
+  public getCurrentSelectedChordIndex(): number {
+    return this.currentSelectedChordIndex;
+  }
+
+  public setCurrentSelectedChordIndex(index: number): void {
+    this.currentSelectedChordIndex = index;
+  }
+
+  public getCurrentChordCursorPitch(): number | null {
+    return this.currentChordCursorPitch;
+  }
+
+  public setCurrentChordCursorPitch(pitch: number | null): void {
+    this.currentChordCursorPitch = pitch;
+  }
 }

src/hooks/useNoteOperations.ts

@@ -10,6 +10,7 @@ import { KGCore } from '../core/KGCore';
 import { KGPianoRollState } from '../core/state/KGPianoRollState';
 import { KGAudioInterface } from '../core/audio-interface/KGAudioInterface';
 import { CreateNoteCommand, DeleteNotesCommand, ResizeNotesCommand, MoveNotesCommand } from '../core/commands';
+import { CreateNotesCommand } from '../core/commands/note/CreateNotesCommand';
 
 interface UseNoteOperationsProps {
   activeRegion: KGMidiRegion | null;
@@ -210,20 +211,64 @@ export const useNoteOperations = ({
     const lastEditedLength = KGPianoRollState.instance().getLastEditedNoteLength();
     const noteEndBeat = noteStartBeat + lastEditedLength; // Use last edited note length
     const velocity = 127; // Maximum velocity
+    const pianoRollState = KGPianoRollState.instance();
+    const matchingChordPitches = pianoRollState.getCurrentMatchingChords();
+    const selectedChordIndex = pianoRollState.getCurrentSelectedChordIndex();
+    const cursorChordPitch = pianoRollState.getCurrentChordCursorPitch();
+    const chordIndex = matchingChordPitches.length > 0
+      ? ((selectedChordIndex % matchingChordPitches.length) + matchingChordPitches.length) % matchingChordPitches.length
+      : 0;
 
-    // Create and execute the note creation command
+    let chordNotePitches: number[] = [];
-    const command = new CreateNoteCommand(
+
+    if (
+      matchingChordPitches.length > 0 &&
+      cursorChordPitch !== null &&
+      Math.abs(cursorChordPitch - pitch) <= 1
+    ) {
+      const cursorOctave = Math.floor(cursorChordPitch / 12);
+      const pitchClasses = matchingChordPitches[chordIndex] || [];
+      chordNotePitches = pitchClasses
+        .map(actualPitchClass => {
+          const actualPitch = cursorOctave * 12 + actualPitchClass;
+          return actualPitch >= 0 && actualPitch <= 127 ? actualPitch : null;
+        })
+        .filter((value): value is number => value !== null);
+
+      chordNotePitches = Array.from(new Set(chordNotePitches));
+    }
+
+    const notePitchesToCreate = chordNotePitches.length > 0 ? chordNotePitches : [pitch];
+    const isChordCreation = notePitchesToCreate.length > 1;
+
+    let createdNotes: KGMidiNote[] = [];
+
+    if (isChordCreation) {
+      const chordCommand = new CreateNotesCommand(
+        notePitchesToCreate.map(notePitch => ({
+          regionId: activeRegion.getId(),
+          startBeat: noteStartBeat,
+          endBeat: noteEndBeat,
+          pitch: notePitch,
+          velocity
+        }))
+      );
+      core.executeCommand(chordCommand);
+      createdNotes = chordCommand.getCreatedNotes().map(({ note }) => note);
+    } else {
+      const singleNoteCommand = new CreateNoteCommand(
         activeRegion.getId(),
         noteStartBeat,
         noteEndBeat,
-      pitch,
+        notePitchesToCreate[0],
         velocity
       );
-
+      core.executeCommand(singleNoteCommand);
-    core.executeCommand(command);
+      const createdNote = singleNoteCommand.getCreatedNote();
-
+      if (createdNote) {
-    // Get the created note for audio preview
+        createdNotes = [createdNote];
-    const createdNote = command.getCreatedNote();
+      }
+    }
 
     // Increment the note update counter to trigger a re-render
     setNoteUpdateCounter((prev: number) => prev + 1);
@@ -238,19 +283,19 @@ export const useNoteOperations = ({
       updateTrack(track);
       
       // Play note preview if audio interface is ready and note was created
-      if (createdNote) {
+      if (createdNotes.length > 0) {
         const audioInterface = KGAudioInterface.instance();
         if (audioInterface.getIsInitialized()) {
-          // Try to start audio context if not started yet (user interaction will allow this)
           if (!audioInterface.getIsAudioContextStarted()) {
             audioInterface.startAudioContext().catch(() => {
               // Silently fail if still not allowed - browser policy
             });
           }
 
-          // Trigger note if audio context is now started
           if (audioInterface.getIsAudioContextStarted()) {
-            audioInterface.triggerNote(track.getId().toString(), createdNote);
+            createdNotes.forEach(note => {
+              audioInterface.triggerNote(track.getId().toString(), note);
+            });
           }
         }
       }