char-slop/chordpad.vibed.software

git clone https://git.t4t.associates/char-slop/chordpad.vibed.software

Charlotte Somcbor project file formata5e999d2026-09-30

import type { Key, ModeId } from "../theory/key.ts";
import { parseNote, pcOf } from "../theory/pitch.ts";

export type NoteEvent = { id: string; start: number; dur: number; pitch: number; vel: number };
/** how hard new notes are played: a midi velocity, as they're saved */
export const NOTE_VEL = 96 / 127;

/** a chord is what was typed, what was voiced by hand, or both. times are in beats */
export type ChordEvent = {
  id: string;
  start: number;
  dur: number;
  symbol?: string;
  notes?: number[];
};

type TrackBase = {
  id: string;
  name: string;
  muted: boolean;
  /** volume trim, in dB */
  gain: number;
  /** visible pitch range of the piano roll */
  view: { low: number; high: number };
};
export type ChordTrack = TrackBase & {
  kind: "chords";
  chords: ChordEvent[];
  /** whether each chord's lowest note sounds: off when another track carries the bass */
  bass: boolean;
};
export type NoteTrack = TrackBase & { kind: "notes"; notes: NoteEvent[] };
export type Track = ChordTrack | NoteTrack;

export type Project = {
  id: string;
  name: string;
  modified: number;
  bpm: number;
  beatsPerBar: number;
  key: { tonic: string; mode: ModeId };
  /** default length of newly typed chords, in beats */
  chordLength: number;
  /** note grid, in beats */
  grid: number;
  loop: boolean;
  /** what gets looped, in beats; the whole song when absent */
  loopRegion?: { start: number; end: number };
  tracks: Track[];
};

// not randomUUID: that only exists in secure contexts, and this may be served over plain http
export const newId = (): string =>
  Array.from(crypto.getRandomValues(new Uint8Array(4)), b =>
    b.toString(16).padStart(2, "0"),
  ).join("");

export const newChordTrack = (name = "chords"): ChordTrack => ({
  id: newId(),
  name,
  kind: "chords",
  muted: false,
  gain: 0,
  bass: true,
  view: { low: 38, high: 77 },
  chords: [],
});

export const newNoteTrack = (name = "melody"): NoteTrack => ({
  id: newId(),
  name,
  kind: "notes",
  muted: false,
  gain: 0,
  view: { low: 57, high: 88 },
  notes: [],
});

export const UNTITLED = "untitled";

type Timed = { start: number; dur: number };
const events = (t: Track): readonly Timed[] => (t.kind === "chords" ? t.chords : t.notes);

/** nothing worth keeping: never named, and nothing written in it */
export const isBlank = (p: Project): boolean =>
  p.name === UNTITLED && p.tracks.every(t => events(t).length === 0);

export const newProject = (): Project => ({
  id: newId(),
  name: UNTITLED,
  modified: Date.now(),
  bpm: 96,
  beatsPerBar: 4,
  key: { tonic: "C", mode: "ionian" },
  chordLength: 1,
  grid: 0.25,
  loop: true,
  tracks: [newChordTrack(), newNoteTrack()],
});

/** the tonics the key picker offers */
export const TONICS = [
  "C",
  "C#",
  "Db",
  "D",
  "D#",
  "Eb",
  "E",
  "F",
  "F#",
  "Gb",
  "G",
  "G#",
  "Ab",
  "A",
  "A#",
  "Bb",
  "B",
];

/** a tonic as the key picker spells it (D♯ → E♭, C♭ → B) */
export function pickableTonic(tonic: string): string {
  const note = parseNote(tonic)?.note;
  if (!note || TONICS.includes(tonic)) return note ? tonic : "C";
  return TONICS.find(t => pcOf(parseNote(t)!.note) === pcOf(note))!;
}

/** a piano roll range that fits these pitches, at least two and a half octaves tall */
export function fitView(pitches: readonly number[]): { low: number; high: number } {
  const [lo, hi] = [Math.min(...pitches), Math.max(...pitches)];
  const span = Math.max(31, hi - lo + 6);
  const low = Math.min(127 - span, Math.max(0, Math.round((lo + hi - span) / 2)));
  return { low, high: low + span };
}

/** a key as projects store it, for working with */
export const keyOf = (key: Project["key"]): Key => ({
  tonic: parseNote(key.tonic)!.note,
  mode: key.mode,
});

export const projectKey = (p: Project): Key => keyOf(p.key);

export const projectEnd = (p: Project): number =>
  Math.max(0, ...p.tracks.flatMap(t => events(t).map(e => e.start + e.dur)));

export function findTrack<K extends Track["kind"]>(
  p: Project,
  id: string,
  kind: K,
): Extract<Track, { kind: K }> | undefined {
  const t = p.tracks.find(t => t.id === id);
  return t?.kind === kind ? (t as Extract<Track, { kind: K }>) : undefined;
}

/**
 * chord boundaries are compared exactly, but sums of triplet positions drift in floating point
 * (4/3 + 1/3 falls just short of 5/3). rounding every boundary onto a fixed grid that holds both
 * 64ths and triplets keeps equal positions equal
 */
export const canonBeat = (beats: number): number => Math.round(beats * 192) / 192;

/** put a chord in place, cutting away whatever it overlaps */
export function placeChord(track: ChordTrack, placed: ChordEvent): void {
  const chord = { ...placed, start: canonBeat(placed.start), dur: canonBeat(placed.dur) };
  const end = canonBeat(chord.start + chord.dur);
  track.chords = track.chords.flatMap(c => {
    if (c.id === chord.id) return [];
    const cEnd = canonBeat(c.start + c.dur);
    if (cEnd <= chord.start || c.start >= end) return [c];
    const kept: ChordEvent[] = [];
    if (c.start < chord.start) kept.push({ ...c, dur: canonBeat(chord.start - c.start) });
    if (cEnd > end) {
      const id = kept.length ? newId() : c.id;
      kept.push({ ...c, id, start: end, dur: canonBeat(cEnd - end) });
    }
    return kept;
  });
  track.chords.push(chord);
  track.chords.sort((a, b) => a.start - b.start);
}

/**
 * put chords just before a target chord, to lead into it: in the back half of the chord before
 * it, so the target still lands where it was; or, with nothing right before, in the target's own
 * front half. false if there isn't room for them on the grid
 */
export function insertLeadIn(
  track: ChordTrack,
  targetId: string,
  symbols: readonly string[],
  grid: number,
): boolean {
  const target = track.chords.find(c => c.id === targetId);
  if (!target) return false;
  const before = track.chords.find(c => canonBeat(c.start + c.dur) === target.start);
  const half = (dur: number) => Math.floor(dur / 2 / grid) * grid;
  const needed = symbols.length * grid;

  let start: number;
  let span: number;
  if (before && half(before.dur) >= needed) {
    span = half(before.dur);
    before.dur = canonBeat(before.dur - span);
    start = canonBeat(target.start - span);
  } else if (half(target.dur) >= needed) {
    span = half(target.dur);
    start = target.start;
    target.start = canonBeat(target.start + span);
    target.dur = canonBeat(target.dur - span);
  } else return false;

  const each = span / symbols.length;
  symbols.forEach((symbol, i) => {
    const at = canonBeat(start + i * each);
    track.chords.push({
      id: newId(),
      start: at,
      dur: canonBeat(start + (i + 1) * each) - at,
      symbol,
    });
  });
  track.chords.sort((a, b) => a.start - b.start);
  return true;
}

/** chords taken out of a track, their starts relative to the first */
export type ChordClip = { chords: Omit<ChordEvent, "id">[]; span: number };

export function copyChords(track: ChordTrack, ids: readonly string[]): ChordClip | undefined {
  const chosen = track.chords.filter(c => ids.includes(c.id));
  if (!chosen.length) return undefined;
  const first = chosen[0].start;
  return {
    chords: chosen.map(({ id: _, ...c }) => ({ ...c, start: canonBeat(c.start - first) })),
    span: canonBeat(Math.max(...chosen.map(c => c.start + c.dur)) - first),
  };
}

/** put copied chords in at a beat, over whatever's there; gives the new chords' ids */
export function pasteChords(track: ChordTrack, clip: ChordClip, at: number): string[] {
  return clip.chords.map(c => {
    const id = newId();
    placeChord(track, { ...structuredClone(c), id, start: at + c.start });
    return id;
  });
}

/** notes taken out of a track, their starts relative to the first */
export type NoteClip = { notes: Omit<NoteEvent, "id">[]; span: number };

export function copyNotes(track: NoteTrack, ids: readonly string[]): NoteClip | undefined {
  const chosen = track.notes.filter(n => ids.includes(n.id));
  if (!chosen.length) return undefined;
  const first = Math.min(...chosen.map(n => n.start));
  return {
    notes: chosen
      .map(({ id: _, ...n }) => ({ ...n, start: n.start - first }))
      .sort((a, b) => a.start - b.start || a.pitch - b.pitch),
    span: Math.max(...chosen.map(n => n.start + n.dur)) - first,
  };
}

/** add copied notes at a beat, alongside what's there; gives the new notes' ids */
export function pasteNotes(track: NoteTrack, clip: NoteClip, at: number): string[] {
  return clip.notes.map(n => {
    const id = newId();
    track.notes.push({ ...n, id, start: at + n.start });
    return id;
  });
}

/** move a track to before the one at `to` (or to the end, at the track count) */
export function moveTrack(p: Project, id: string, to: number): void {
  const from = p.tracks.findIndex(t => t.id === id);
  const [track] = p.tracks.splice(from, 1);
  p.tracks.splice(from < to ? to - 1 : to, 0, track);
}