ISSUE-E7-02 — Extract Repeated Chord-Note Retrieval into a Shared Utility

[JWWade]

ISSUE-E7-02 — Extract Repeated Chord-Note Retrieval into a Shared Utility

Objective

Replace a copy-pasted conditional that retrieves pitch classes from a Chord value with a single reusable utility function, removing the duplication from at least five files.

Background

The following pattern appears verbatim (or near-verbatim) in multiple files across the codebase:

isCustomChord(chord) ? chord.customNotes : getChordNoteIndices(chord.root, chord.type)

Known locations (non-exhaustive):

• client/src/features/current-chord/components/CurrentChordPanel.tsx
• client/src/features/progression-sidebar/components/ChordTile.tsx
• client/src/features/progression-sidebar/components/ProgressionSidebar.tsx
• client/src/features/midi-export/utils/midiBuilder.ts
• client/src/features/progression-sidebar/utils/pairMetrics.ts

Each duplicate is a maintenance hazard: introducing a new chord variant (e.g., quartal chords) requires hunting down and updating every occurrence. A single function eliminates that risk.

Proposed API

// client/src/features/chord/utils/getChordPitchClasses.ts
export function getChordPitchClasses(chord: Chord): number[]

The function should:

1. Check isCustomChord(chord) and return chord.customNotes if true.
2. Otherwise call getChordNoteIndices(chord.root, chord.type) and return the result.

Files To Add

• client/src/features/chord/utils/getChordPitchClasses.ts — new utility function.

Files To Edit

• client/src/features/chord/utils/index.ts — re-export getChordPitchClasses.
• All files listed in Known locations above — replace inline conditionals with a call to getChordPitchClasses(chord).

Acceptance Criteria

• getChordPitchClasses(chord: Chord): number[] exists in client/src/features/chord/utils/.
• No file outside getChordPitchClasses.ts contains the pattern isCustomChord(chord) ? chord.customNotes.
• All existing tests pass.
• npm run lint passes with --max-warnings=0.
• npm run build succeeds with no TypeScript errors.

Verification Commands

cd client
npm run lint
npm run build
npm test