import { NextRequest } from "next/server";
import { spawn, type ChildProcess } from "node:child_process";
import fsp from "node:fs/promises";
import { findVideosForCode, getVideoIndex, rescanVideoIndex } from "@/lib/video";
import { getAppSetting } from "@/lib/db/appSettings";
import { probeDuration } from "@/lib/video/duration";
import { assertLocalRequest } from "@/lib/api/localOnly";

export const runtime = "nodejs";
export const dynamic = "force-dynamic";

/**
 * HLS segment endpoint. Each request transcodes a single 6-second
 * window of the source via NVENC into MPEG-TS and pipes to the
 * response. -bf 0 keeps Chromium's H.264 sink happy. -force_key_frames
 * 0 (and NVENC's -forced-idr) ensure the segment opens with an IDR so
 * it's independently decodable — required by HLS.
 */
const SEGMENT_SECONDS = 6;

export async function GET(req: NextRequest, ctx: { params: Promise<{ code: string }> }) {
  const blocked = assertLocalRequest(req);
  if (blocked) return blocked;

  const { code } = await ctx.params;
  const decoded = decodeURIComponent(code);
  const url = new URL(req.url);
  const partRaw = url.searchParams.get("part");
  const part = partRaw == null ? 0 : Math.max(0, parseInt(partRaw, 10) || 0);
  const iRaw = url.searchParams.get("i");
  const segmentIndex = iRaw == null ? 0 : Math.max(0, parseInt(iRaw, 10) || 0);

  let files = findVideosForCode(decoded);
  if (files.length === 0) {
    const main = (getAppSetting("videoLibraryPath") || "").trim();
    const extras = getAppSetting("videoExtraPaths") ?? [];
    const expected = [main, ...extras].filter(Boolean);
    const idx = getVideoIndex();
    const haveAll = expected.length === idx.rootsScanned.length
      && expected.every((r, i) => r === idx.rootsScanned[i]);
    if (expected.length > 0 && !haveAll) {
      await rescanVideoIndex();
      files = findVideosForCode(decoded);
    }
  }
  if (files.length === 0) return new Response("not found", { status: 404 });
  const file = files[Math.min(part, files.length - 1)];

  try {
    await fsp.stat(file.abs);
  } catch {
    return new Response("not found", { status: 404 });
  }

  const duration = await probeDuration(file.abs, req.signal);
  if (duration == null) {
    return new Response("ffprobe failed", { status: 500 });
  }

  const startTime = segmentIndex * SEGMENT_SECONDS;
  if (startTime >= duration) {
    return new Response("segment out of range", { status: 416 });
  }
  const segDur = Math.min(SEGMENT_SECONDS, duration - startTime);

  const ffmpegArgs: string[] = [
    "-hide_banner", "-loglevel", "error",
    // -ss before -i = fast container-level seek (lands on the prior key
    // frame, NVENC's first emitted frame is an IDR by spec).
    "-ss", startTime.toFixed(3),
    "-t", segDur.toFixed(3),
    "-i", file.abs,
    "-map", "0:v:0",
    "-map", "0:a:0?",
    "-c:v", "h264_nvenc",
    "-preset", "p4",
    "-tune", "ll",
    "-profile:v", "high",
    "-bf", "0",
    "-forced-idr", "1",
    "-rc", "cbr",
    "-b:v", "8M",
    "-maxrate", "8M",
    "-bufsize", "16M",
    "-pix_fmt", "yuv420p",
    "-c:a", "aac",
    "-b:a", "192k",
    "-ac", "2",
    "-f", "mpegts",
    "-mpegts_flags", "+resend_headers",
    // Shift output timestamps so segment N's PTS starts at N*SEGMENT_SECONDS.
    // Without this, every segment would emit at PTS≈0 and hls.js / MSE
    // can't lay them out on a continuous timeline (would need
    // #EXT-X-DISCONTINUITY markers for that). Continuous PTS = clean
    // append, smooth playback across segment boundaries.
    "-output_ts_offset", startTime.toFixed(3),
    "pipe:1",
  ];

  let ffmpeg: ChildProcess;
  try {
    ffmpeg = spawn("ffmpeg", ffmpegArgs, { stdio: ["ignore", "pipe", "pipe"] });
  } catch (e) {
    return new Response(`ffmpeg spawn failed: ${(e as Error).message}`, { status: 500 });
  }
  ffmpeg.stderr?.on("data", (chunk: Buffer) => {
    const text = chunk.toString();
    if (text.trim()) console.error(`[hls ${decoded} seg=${segmentIndex}] ${text.trim()}`);
  });

  return new Response(streamFromFfmpeg(ffmpeg, req.signal), {
    status: 200,
    headers: {
      "Content-Type": "video/mp2t",
      // Allow short-term caching — within a single playback session hls.js
      // may re-request a segment if its buffer was evicted, and a cache
      // hit avoids re-spawning ffmpeg.
      "Cache-Control": "private, max-age=300",
    },
  });
}

function streamFromFfmpeg(proc: ChildProcess, signal: AbortSignal): ReadableStream<Uint8Array> {
  return new ReadableStream<Uint8Array>({
    start(controller) {
      let closed = false;
      const finish = () => {
        if (closed) return;
        closed = true;
        try { controller.close(); } catch { /* already closed */ }
      };
      const fail = (err: Error) => {
        if (closed) return;
        closed = true;
        try { controller.error(err); } catch { /* already closed */ }
      };
      proc.stdout?.on("data", (chunk: Buffer) => {
        if (closed) return;
        try {
          controller.enqueue(new Uint8Array(chunk));
        } catch {
          closed = true;
          try { proc.kill("SIGKILL"); } catch { /* ignore */ }
        }
      });
      proc.stdout?.on("end", finish);
      proc.on("error", (e) => fail(e));
      proc.on("exit", finish);

      const onAbort = () => {
        try { proc.kill("SIGKILL"); } catch { /* ignore */ }
      };
      if (signal.aborted) onAbort();
      else signal.addEventListener("abort", onAbort, { once: true });
    },
    cancel() {
      try { proc.kill("SIGKILL"); } catch { /* ignore */ }
    },
  });
}