// Playback level: absolute (fixed pascal-to-full-scale mapping with a user gain),
// loudness normalization, or peak normalization. A soft clipper bounds the output.

export type LevelMode = "absolute" | "loudness" | "peak";

/** Linear gain applied to the pressure signal [Pa] for the given mode. */
export function levelGain(samples: Float32Array, fs: number, mode: LevelMode, gainDb: number, peak = 0.95): number {
  if (samples.length === 0) return 0;
  if (mode === "absolute") {
    // 0 dBFS corresponds to 1 Pa at 0 dB gain.
    return 10 ** (gainDb / 20);
  }
  if (mode === "peak") {
    let max = 0;
    for (let k = 0; k < samples.length; k++) max = Math.max(max, Math.abs(samples[k]));
    return max > 0 ? peak / max : 0;
  }
  // Loudness: scale the RMS of the sustained part (after the first 50 ms) to -16 dBFS.
  const start = Math.min(samples.length - 1, Math.round(0.05 * fs));
  let sum = 0;
  for (let k = start; k < samples.length; k++) sum += samples[k] * samples[k];
  const rms = Math.sqrt(sum / Math.max(1, samples.length - start));
  return rms > 0 ? 10 ** (-16 / 20) / rms : 0;
}

/** Peak level [dBFS] the signal would reach before clipping. */
export function peakDbfs(samples: Float32Array, gain: number): number {
  let max = 0;
  for (let k = 0; k < samples.length; k++) max = Math.max(max, Math.abs(samples[k]));
  return max > 0 ? 20 * Math.log10(max * gain) : -Infinity;
}

/** Returns a copy of `samples` scaled for playback or export, soft-clipped to [-peak, peak]. */
export function normalize(samples: Float32Array, fs: number, mode: LevelMode, gainDb: number, peak = 0.95): Float32Array {
  const out = new Float32Array(samples.length);
  const g = levelGain(samples, fs, mode, gainDb, peak);
  if (mode === "peak") {
    for (let k = 0; k < samples.length; k++) out[k] = samples[k] * g;
    return out;
  }
  for (let k = 0; k < samples.length; k++) out[k] = peak * Math.tanh((samples[k] * g) / peak);
  return out;
}