import { createHash } from "node:crypto";
import { existsSync } from "node:fs";
import { mkdir, readFile, rename } from "node:fs/promises";
import { execFile } from "node:child_process";
import { promisify } from "node:util";
import { CACHE_DIR, cacheFile } from "@/lib/paths";
import { sourceVideo } from "@/lib/clips";

const run = promisify(execFile);

export const dynamic = "force-dynamic";

// The PICTURE for the window being judged.
//
// Judging by waveform and ear alone throws away the one signal that settles the
// hardest question this tool asks: is this Jer, or the other person in the room?
// The pitch gate exists precisely because interviews carry a guest, and a guest
// is obvious on sight and ambiguous by ear. The face is also how "is this even a
// filler" gets answered quickly -- a laugh, a cough and an um look nothing alike.
//
// Served for the SAME window as the audio route so the two share one time base:
// the player can be positioned with (playFrom - view.from) and needs no second
// mapping. Cached on the same key scheme, and small on purpose -- this is a
// reference thumbnail, not a viewing copy.
export async function GET(request: Request, ctx: { params: Promise<{ key: string }> }) {
  const { key } = await ctx.params;
  const url = new URL(request.url);
  const from = Number(url.searchParams.get("from"));
  const to = Number(url.searchParams.get("to"));
  if (!Number.isFinite(from) || !Number.isFinite(to) || to <= from) {
    return new Response("bad window", { status: 400 });
  }

  const decoded = decodeURIComponent(key);
  const at = decoded.lastIndexOf("@");
  const video = at > 0 ? decoded.slice(0, at) : decoded;
  const file = sourceVideo(video);
  // Not every source has media/ -- it is bulk data and re-derivable. A missing
  // file is a normal state, not an error: the client simply shows no player.
  if (!existsSync(file)) return new Response("no video", { status: 404 });

  const stamp = createHash("sha1")
    .update(`v1|${video}|${from.toFixed(3)}|${to.toFixed(3)}`)
    .digest("hex")
    .slice(0, 16);
  // Through cacheFile, never a join here: see its comment in lib/paths.mjs.
  const cached = cacheFile(`${stamp}.mp4`);
  if (existsSync(cached)) {
    return new Response(new Uint8Array(await readFile(cached)), {
      headers: { "content-type": "video/mp4", "cache-control": "no-store" },
    });
  }

  await mkdir(CACHE_DIR, { recursive: true });
  const tmp = cacheFile(`${stamp}.mp4.tmp.mp4`);
  // -ss BEFORE -i for the fast seek, then -t for the length. Re-encoded rather
  // than copied because a stream copy starts at the previous keyframe, which
  // would slide the picture against the audio by up to several seconds.
  await run("ffmpeg", [
    "-nostdin", "-v", "error", "-y",
    "-ss", from.toFixed(3), "-t", (to - from).toFixed(3), "-i", file,
    "-an", "-vf", "scale=360:-2,fps=25",
    "-c:v", "libx264", "-preset", "veryfast", "-crf", "30", "-pix_fmt", "yuv420p",
    "-movflags", "+faststart", tmp,
  ]);
  await rename(tmp, cached).catch(() => {});

  return new Response(new Uint8Array(await readFile(cached)), {
    headers: { "content-type": "video/mp4", "cache-control": "no-store" },
  });
}