#!/usr/bin/env node
// Silence a leading region of a hook WITHOUT changing its duration.
//
//   node hush-head.mjs <in.wav> <out.wav> <until> [fade]
//
// Why not just trim the head off: every hook is placed by its FILE START. The
// overlays give an `at` per occurrence (mk-mix-hooks.mjs delays the clip by it),
// and those times were set by ear against the game's own events -- the silent gap
// at 17.15-18.086s, the gong, the fanfare. Cutting N seconds off the front moves
// the shout N seconds earlier at every occurrence and quietly breaks all of it.
// Silencing in place is the same edit with none of that: the file is the same
// length, the shout stays exactly where it was judged to be, and only the
// unwanted sound goes away.
//
// The other reason to prefer it: the catalogue's `gain` is a PEAK TARGET, so the
// clip's loudest sample decides how loud the shout ends up. Silencing a head
// whose peak is BELOW the shout's leaves the level untouched (verify with the
// printed peaks); cutting one that is ABOVE it makes the shout louder, which is
// usually the point but is a change that should be seen rather than discovered.
//
// FADE avoids a click: a hard cut at a non-zero sample is more obvious than
// whatever is being removed, the same reason apply-hook-trims.mjs fades its cuts.
import { execFileSync } from "node:child_process";

const [IN, OUT, UNTIL, FADE = "0.030"] = process.argv.slice(2);
if (!IN || !OUT || !UNTIL) {
  console.error("usage: node hush-head.mjs <in.wav> <out.wav> <until> [fade]");
  process.exit(1);
}
const until = Number(UNTIL), fade = Number(FADE);

const peakOf = (file, from, to) => {
  const b = execFileSync("ffmpeg", ["-v", "error", "-ss", String(from), "-to", String(to),
    "-i", file, "-ac", "1", "-ar", "48000", "-f", "s16le", "-"], { maxBuffer: 1 << 28 });
  const a = new Int16Array(b.buffer, b.byteOffset, b.length / 2);
  let p = 0;
  for (let i = 0; i < a.length; i += 1) p = Math.max(p, Math.abs(a[i] / 32768));
  return p;
};

const dur = Number(execFileSync("ffprobe", ["-v", "error", "-show_entries", "format=duration",
  "-of", "csv=p=0", IN]).toString().trim());
const headPeak = peakOf(IN, 0, until);
const restPeak = peakOf(IN, until, dur);

// eval=frame because the expression is time-varying; the same idiom the finale
// envelope in mk-fatal-finish3.sh uses.
const VOL = `if(lt(t,${until}),0,if(lt(t,${until + fade}),(t-${until})/${fade},1))`;
execFileSync("ffmpeg", ["-y", "-v", "error", "-i", IN,
  "-af", `volume='${VOL}':eval=frame`, OUT]);

console.log(`${IN} -> ${OUT}`);
console.log(`  silenced 0-${until}s (peak ${headPeak.toFixed(4)}), kept ${until}-${dur.toFixed(3)}s (peak ${restPeak.toFixed(4)})`);
console.log(`  duration unchanged: ${dur.toFixed(3)}s — every 'at' in the overlays still lands where it was judged`);
if (headPeak > restPeak) {
  console.log(`  NOTE: the head WAS the clip's peak, so a peak-targeted gain will now play the shout louder`);
}