import { sounding, voiceTrack } from "../project/harmony.ts";
import { type Project, projectKey } from "../project/model.ts";
import { MODES } from "../theory/key.ts";
import { spellDegree } from "../theory/pitch.ts";
import { type OutTrack, writeMidi } from "./write.ts";

const ELECTRIC_PIANO = 4;
const DRUM_CHANNEL = 9;

/** a project as a midi file: chords as they're voiced, every track on its own channel */
export function projectMidi(p: Project): Uint8Array<ArrayBuffer> {
  const key = projectKey(p);
  const channels = [...Array(16).keys()].filter(c => c !== DRUM_CHANNEL);

  const tracks = p.tracks.map((track, i): OutTrack => ({
    name: track.name,
    channel: channels[i % channels.length],
    program: ELECTRIC_PIANO,
    notes:
      track.kind === "notes"
        ? track.notes
        : voiceTrack(track, key).flatMap(({ event, notes }) =>
            sounding(track, notes).map(pitch => ({
              start: event.start,
              dur: event.dur,
              pitch,
              vel: 0.55,
            })),
          ),
  }));

  // a key signature only knows major and minor: modes get their parent scale's signature
  const minor = ["aeolian", "harmonicMinor", "melodicMinor"].includes(key.mode);
  const steps = minor ? MODES.aeolian.steps : MODES[key.mode].steps;
  const accidentals = steps.reduce((n, s, d) => n + spellDegree(key.tonic, d, s).acc, 0);

  return writeMidi({
    bpm: p.bpm,
    beatsPerBar: p.beatsPerBar,
    key: { accidentals, minor },
    tracks,
  });
}