/**
 * normalize-size.ts — picking the canvas for a mixed-size concat.
 *
 * The demuxer concat path uses `-c copy`, which assumes every segment shares
 * stream parameters. When they do not, ffmpeg does NOT error: it emits a master
 * with a wrong duration and frame rate that looks entirely plausible (a 3x15s
 * mixed 1080p/720p film once came out as 108s at ~10fps, rc=0, and nothing
 * downstream noticed). So the prep pass re-encodes every segment to one size —
 * and this module decides which size that is.
 */

/**
 * The size to normalise a mixed-size concat to: whichever frame size the most
 * segments already have, ties broken toward the LARGER (so a 50/50 split keeps
 * the detail rather than discarding it).
 *
 * PURE — the probing lives in `stitch`. Exported for the unit tests, because the
 * cost of getting this wrong is invisible: ffmpeg does not error on a mixed
 * concat, it emits a master with a wrong duration and frame rate that looks
 * plausible.
 */
export function majoritySize(
  sizes: ReadonlyArray<{ width: number; height: number }>,
): { width: number; height: number } {
  const counts = new Map<string, { size: { width: number; height: number }; n: number }>();
  for (const size of sizes) {
    const key = `${size.width}x${size.height}`;
    const hit = counts.get(key);
    if (hit) hit.n += 1;
    else counts.set(key, { size, n: 1 });
  }
  let best: { size: { width: number; height: number }; n: number } | undefined;
  for (const entry of counts.values()) {
    if (
      best === undefined ||
      entry.n > best.n ||
      (entry.n === best.n && entry.size.width * entry.size.height > best.size.width * best.size.height)
    ) {
      best = entry;
    }
  }
  return best!.size;
}