Pitch classes et al

music.ts

// Duration
export type Duration = number;
const PPQ: Duration = 960;

export const wn = 4 * PPQ; // whole note duration
export const hn = (1 / 2) * wn; // half note duration
export const qn = (1 / 4) * wn; // quarter note duration
export const en = (1 / 8) * wn; // eight note duration
export const sn = (1 / 16) * wn; // sixteenth note duration
export const tn = (1 / 32) * wn; // thirty-second note duration
export const sfn = (1 / 64) * wn; // sixty-fourth note duration

export const dwn = (3 / 2) * wn; // dotted whole note duration
export const dhn = (3 / 4) * wn; // dotted half note duration
export const dqn = (3 / 8) * wn; // dotted quarter note duration
export const den = (3 / 16) * wn; // dotted eight note duration
export const dsn = (3 / 32) * wn; //dotted  sixteenth note duration
export const dtn = (3 / 64) * wn; //dotted  thirty-second note duration

export const ddhn = (7 / 8) * wn; // double-dotted half note duration
export const ddqn = (7 / 16) * wn; // double-dotted quarter note duration
export const dden = (7 / 32) * wn; // double-dotted eightnote duration

export type Midi = number;
export type Octave = number;

export enum PitchClass {
  Cff = "Cbb",
  Cf = "Cb",
  C = "C",
  Dff = "Dbb",
  Cs = "C#",
  Df = "Db",
  Css = "C##",
  D = "D",
  Eff = "Ebb",
  Ds = "D#",
  Ef = "Eb",
  Fff = "F##",
  Dss = "D##",
  E = "E",
  Ff = "Fb",
  Es = "E#",
  F = "F",
  Gff = "Gbb",
  Ess = "E##",
  Fs = "F#",
  Gf = "Gb",
  Fss = "F##",
  G = "G",
  Aff = "Abb",
  Gs = "G#",
  Af = "Ab",
  Gss = "G##",
  A = "A",
  Bff = "Bbb",
  As = "A#",
  Bf = "Bb",
  Ass = "A##",
  B = "B",
  Bs = "B#",
  Bss = "B##"
}

export type Pitch = ["pitch", PitchClass, Octave];

const ACCIDENTALS = ["bb", "b", "", "#", "##"];
const pitch = (base: PitchClass) => (oct: Octave, alt: number = 0): Pitch => {
  const acc = ACCIDENTALS[alt + 2];
  return ["pitch", base + acc, oct] as Pitch;
};

export function isPitch(p: Pitch | Array<any>): p is Pitch {
  return p[0] === "pitch";
}

export const C = pitch(PitchClass.C);
export const D = pitch(PitchClass.D);
export const E = pitch(PitchClass.E);
export const F = pitch(PitchClass.F);
export const G = pitch(PitchClass.G);
export const A = pitch(PitchClass.A);
export const B = pitch(PitchClass.B);

export interface Music {
  duration: Duration;
}

export interface Primitive extends Music {
  pitch: Pitch | null;
}

export interface Rest extends Primitive {
  pitch: null;
}

export interface Note extends Primitive {
  pitch: Pitch;
  [propName: string]: any;
}

export function rest(duration = PPQ): Rest {
  return { duration, pitch: null };
}

export const Nothing = rest(0);

export function note(pitch: Pitch, duration = PPQ): Note {
  return { pitch, duration };
}

export function strToNote(str: string, duration = PPQ): Primitive {
  // FIXME: needs implementation
  return Nothing;
}

export function midiToNote(midi: Midi, duration = PPQ): Primitive {
  // FIXME: needs implementation
  return Nothing;
}

export function noteToMidi(note: Note): Midi {
  return 0;
}

export type Tempo = number;
export type Transpose = number;
export enum Mode {
  Major = "major",
  Minor = "minor"
}
export type KeySig = [PitchClass, Mode];