import { existsSync } from "node:fs";
import { TRIM_SETS, stemPath } from "@/lib/trim";
import { readWavWindow, encodeWav } from "@/lib/wav";

export const dynamic = "force-dynamic";

// A window of the stem, to audition a trim against.
//
// Served as WAV, always, and with NO gain applied.
//
// The clip audio route normalises against a fixed reference region so that
// widening the view does not change the level. Here the simpler answer is the
// right one: applying no gain at all has the same property -- what you hear at
// one width is what you hear at another -- and it is also what actually gets
// cut, since apply-hook-trims only ever atrims and fades. A hook is a couple of
// seconds, so there is nothing for an encoder to save.

export async function GET(request: Request, ctx: { params: Promise<{ set: string }> }) {
  const { set: id } = await ctx.params;
  const set = TRIM_SETS[id];
  if (!set) return new Response("no such trim set", { status: 404 });

  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 });
  }
  // A runaway window would decode the whole stem into memory on every request.
  if (to - from > 120) return new Response("window too long", { status: 400 });

  const file = stemPath(set);
  if (!existsSync(file)) return new Response("stem missing", { status: 404 });

  const region = await readWavWindow(file, Math.max(0, from), to);
  const buf = encodeWav(region.x, region.sampleRate);
  return new Response(new Uint8Array(buf), {
    headers: {
      "content-type": "audio/wav",
      "content-length": String(buf.length),
      "cache-control": "no-store",
    },
  });
}