import {
  describeFrequencyAliasing,
  observeFrequencyBand,
} from "/packages/acoustics-core/sampling.js";

/**
 * Select evaluation truth sources for one observed band.
 *
 * Arrival ids come from synthesis path timing and take precedence over the
 * legacy emission-time fallback. This helper is evaluation-only; localization
 * never receives truth positions or ids.
 */
export function sourcesForObservedBand(
  scene,
  band,
  fftSize,
  options = {},
) {
  const observation = observeFrequencyBand(band, scene.sampleRate, fftSize);
  const observedBins = new Set(observation.bins);
  const arrivingSourceIdSet = Array.isArray(options.arrivingSourceIds)
    ? new Set(options.arrivingSourceIds)
    : null;
  const time = options.time ?? null;
  return scene.sources.filter((source) => {
    if (arrivingSourceIdSet) {
      if (!arrivingSourceIdSet.has(source.id)) return false;
    } else if (time !== null) {
      const startTime = source.startTime ?? 0;
      const endTime = startTime + (source.duration ?? scene.duration);
      if (time < startTime || time >= endTime) return false;
    }
    if (source.signal.type !== "tone") return true;
    const analogInside =
      source.signal.frequency >= band.minHz && source.signal.frequency <= band.maxHz;
    if (analogInside) return true;
    const alias = describeFrequencyAliasing(source.signal.frequency, scene.sampleRate);
    const nearestAdcBin = Math.round(alias.adcFrequencyHz / observation.binWidthHz);
    return observedBins.has(nearestAdcBin);
  });
}