/**
 * Placeholder drum voices on an OfflineAudioContext: a pitch-dropping sine
 * for the kick and tom, filtered noise for the snare and hat. These exist
 * so the capture-classify-arrange loop is playable end to end; the
 * instrawave renderer replaces them behind the same interface.
 */
import type { NoteEvent, SynthPreset } from './types.ts';

const SR = 44100;

export async function renderSynth(
  events: NoteEvent[],
  preset: (voiceId: string) => SynthPreset,
  seconds: number,
): Promise<AudioBuffer> {
  const len = Math.max(1, Math.ceil(seconds * SR));
  const ctx = new OfflineAudioContext(1, len, SR);
  const noise = noiseBuffer(ctx);
  for (const ev of events) {
    const g = Math.max(1e-4, Math.min(1, ev.gain));
    switch (preset(ev.voiceId)) {
      case 'kick': kick(ctx, ev.t, g); break;
      case 'snare': snare(ctx, ev.t, g, noise); break;
      case 'hat': hat(ctx, ev.t, g, noise); break;
      case 'tom': tom(ctx, ev.t, g); break;
    }
  }
  return ctx.startRendering();
}

function noiseBuffer(ctx: OfflineAudioContext): AudioBuffer {
  const buf = ctx.createBuffer(1, SR, SR);
  const x = buf.getChannelData(0);
  let s = 22222; // deterministic; renders are reproducible
  for (let i = 0; i < x.length; i++) {
    s = (s * 1103515245 + 12345) & 0x7fffffff;
    x[i] = (s / 0x3fffffff) - 1;
  }
  return buf;
}

function env(ctx: OfflineAudioContext, t: number, g: number, decay: number): GainNode {
  const gain = ctx.createGain();
  gain.gain.setValueAtTime(g, t);
  gain.gain.exponentialRampToValueAtTime(1e-4, t + decay);
  gain.connect(ctx.destination);
  return gain;
}

function kick(ctx: OfflineAudioContext, t: number, g: number): void {
  const osc = ctx.createOscillator();
  osc.frequency.setValueAtTime(150, t);
  osc.frequency.exponentialRampToValueAtTime(46, t + 0.09);
  osc.connect(env(ctx, t, g, 0.45));
  osc.start(t);
  osc.stop(t + 0.5);
}

function tom(ctx: OfflineAudioContext, t: number, g: number): void {
  const osc = ctx.createOscillator();
  osc.frequency.setValueAtTime(150, t);
  osc.frequency.exponentialRampToValueAtTime(98, t + 0.12);
  osc.connect(env(ctx, t, g * 0.9, 0.3));
  osc.start(t);
  osc.stop(t + 0.35);
}

function snare(ctx: OfflineAudioContext, t: number, g: number, noise: AudioBuffer): void {
  const tone = ctx.createOscillator();
  tone.type = 'triangle';
  tone.frequency.value = 185;
  tone.connect(env(ctx, t, g * 0.4, 0.12));
  tone.start(t);
  tone.stop(t + 0.15);
  const n = ctx.createBufferSource();
  n.buffer = noise;
  const bp = ctx.createBiquadFilter();
  bp.type = 'highpass';
  bp.frequency.value = 900;
  n.connect(bp).connect(env(ctx, t, g * 0.7, 0.2));
  n.start(t, 0, 0.25);
}

function hat(ctx: OfflineAudioContext, t: number, g: number, noise: AudioBuffer): void {
  const n = ctx.createBufferSource();
  n.buffer = noise;
  const hp = ctx.createBiquadFilter();
  hp.type = 'highpass';
  hp.frequency.value = 7000;
  n.connect(hp).connect(env(ctx, t, g * 0.5, 0.06));
  n.start(t, 0, 0.1);
}