import * as at from "@coderline/alphatab";
import type { Audio } from "../core/types.ts";
import { renderMidiFile } from "../audio/render.ts";
import { resample } from "../dsp/resample.ts";
import type { RefTrack } from "./smf.ts";
import type { Warp } from "./warp.ts";

const RENDER_SR = 44100; // alphaSynth yields NaN at other rates (e.g. 22050), so always render here and resample
const TPS = 1920; // division 960 at a fixed 120 bpm
const PEAK = Math.pow(10, -1 / 20);
const MELODIC_CHANNELS = [0, 1, 2, 3, 4, 5, 6, 7, 8, 10, 11, 12, 13, 14, 15];

/**
 * Render reference tracks to audio with `warp` applied (MIDI time -> audio time). Notes are placed on a fixed-tempo
 * tick grid so alphaSynth output time equals audio time. Peak-normalised to -1 dBFS; `durationSec` pads/trims.
 * Pure: no I/O. Notes landing before audio t=0 are clamped to 0 (dropped if they end before it).
 */
export function renderMidi(
  tracks: RefTrack[], warp: Warp, sf2: Uint8Array,
  opts: { sampleRate?: number; mono?: boolean; durationSec?: number } = {},
): Audio {
  const sampleRate = opts.sampleRate ?? RENDER_SR;
  const midi = new at.midi.MidiFile();
  midi.division = 960;
  midi.addEvent(new at.midi.TempoChangeEvent(0, 500000));
  const seen = new Set<number>();
  let next = 0;
  for (const t of tracks) {
    // Beyond 15 melodic tracks channels wrap and are shared; the first track's program wins on a shared channel.
    const ch = t.isDrums ? 9 : MELODIC_CHANNELS[next++ % MELODIC_CHANNELS.length]!;
    if (!seen.has(ch)) { seen.add(ch); midi.addEvent(new at.midi.ProgramChangeEvent(0, 0, ch, t.isDrums ? 0 : t.program)); }
    for (const n of t.notes) {
      const offSec = warp.toAudio(n.offset);
      if (offSec <= 0) continue;
      const on = Math.round(Math.max(0, warp.toAudio(n.onset)) * TPS);
      const off = Math.max(on + 1, Math.round(offSec * TPS));
      midi.addEvent(new at.midi.NoteOnEvent(0, on, ch, n.pitch, n.velocity));
      midi.addEvent(new at.midi.NoteOffEvent(0, off, ch, n.pitch, 0));
    }
  }
  const out = renderMidiFile(midi, sf2, RENDER_SR, { frames: opts.durationSec === undefined ? undefined : Math.round(opts.durationSec * RENDER_SR) });
  let chans = out.channels;
  if (sampleRate !== RENDER_SR) {
    chans = chans.map((c) => resample(c, RENDER_SR, sampleRate));
    if (opts.durationSec !== undefined) { const n = Math.round(opts.durationSec * sampleRate); chans = chans.map((c) => { const o = new Float32Array(n); o.set(c.subarray(0, n)); return o; }); }
  }
  if (opts.mono) {
    const [L, R] = chans as [Float32Array, Float32Array];
    chans = [L.map((v, i) => (v + R[i]!) / 2)];
  }
  for (const c of chans) for (let i = 0; i < c.length; i++) if (!Number.isFinite(c[i]!)) throw new Error("renderMidi: non-finite samples from synth");
  let peak = 0;
  for (const c of chans) for (let i = 0; i < c.length; i++) { const a = Math.abs(c[i]!); if (a > peak) peak = a; }
  if (peak > 0) { const g = PEAK / peak; for (const c of chans) for (let i = 0; i < c.length; i++) c[i]! *= g; }
  return { sampleRate, channels: chans };
}