import { canonBeat } from "../project/model.ts";
import type { MidiNote } from "./smf.ts";

/** a part as a run of chords: a new one wherever the set of sounding notes changes */
export function chordsOf(
  notes: readonly MidiNote[],
): { start: number; dur: number; notes: number[] }[] {
  const spans = notes.map(n => ({
    pitch: n.pitch,
    start: canonBeat(n.start),
    end: canonBeat(n.start + n.dur),
  }));
  const cuts = [...new Set(spans.flatMap(n => [n.start, n.end]))].sort((a, b) => a - b);
  const runs: { start: number; end: number; notes: number[] }[] = [];
  cuts.slice(1).forEach((end, i) => {
    const start = cuts[i];
    const sounding = spans.filter(n => n.start <= start && n.end >= end).map(n => n.pitch);
    if (!sounding.length) return;
    const pitches = [...new Set(sounding)].sort((a, b) => a - b);
    const last = runs.at(-1);
    if (last?.end === start && last.notes.join() === pitches.join()) last.end = end;
    else runs.push({ start, end, notes: pitches });
  });
  return runs.map(({ start, end, notes }) => ({ start, dur: canonBeat(end - start), notes }));
}