import { NextRequest, NextResponse } from "next/server";
import path from "node:path";
import fs from "node:fs/promises";
import { spawn } from "node:child_process";
import { assertLocalRequest } from "@/lib/api/localOnly";
import { srtToVtt, SUBTITLE_EXTS, decodeSubtitleBuffer } from "@/lib/video/subtitles";
import { isAllowedSubtitlePath } from "@/lib/video/subtitleAccess";
import { cachePath, readCache, writeCache } from "@/lib/video/subtitleCache";
import { findVideosForCode } from "@/lib/video";
import { runFfprobeSubtitles } from "@/lib/video/metadata";

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

const VTT_HEADERS = {
  "Content-Type": "text/vtt; charset=utf-8",
  "Cache-Control": "no-store",
} as const;

function decodeSide(src: string): string | null {
  if (!src.startsWith("side:")) return null;
  const b64 = src.slice("side:".length);
  try {
    const decoded = Buffer.from(b64, "base64url").toString("utf8");
    if (!decoded) return null;
    return path.resolve(decoded);
  } catch {
    return null;
  }
}

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

  const src = req.nextUrl.searchParams.get("src") ?? "";
  if (!src) {
    return NextResponse.json({ error: "Missing src" }, { status: 400 });
  }

  if (src.startsWith("emb:")) {
    return handleEmbedded(req, ctx, src);
  }

  const abs = decodeSide(src);
  if (!abs) {
    return NextResponse.json({ error: "Invalid src" }, { status: 400 });
  }
  if (!isAllowedSubtitlePath(abs)) {
    return NextResponse.json({ error: "Subtitle path not allowed" }, { status: 403 });
  }

  const ext = path.extname(abs).toLowerCase();
  if (!(SUBTITLE_EXTS as readonly string[]).includes(ext)) {
    return NextResponse.json({ error: "Unsupported subtitle extension" }, { status: 415 });
  }

  let stat;
  try {
    stat = await fs.stat(abs);
  } catch {
    return NextResponse.json({ error: "Subtitle file not found" }, { status: 404 });
  }

  if (ext === ".vtt") {
    // VTT spec mandates UTF-8 but real-world files occasionally ship
    // as UTF-16 BOM or a legacy Asian encoding. Run through the same
    // decoder as .srt so the output is consistent UTF-8.
    let buf: Buffer;
    try {
      buf = await fs.readFile(abs);
    } catch {
      return NextResponse.json({ error: "Read failed" }, { status: 500 });
    }
    const text = decodeSubtitleBuffer(buf);
    return new NextResponse(text, { headers: VTT_HEADERS });
  }

  if (ext === ".srt") {
    const file = cachePath({
      abs,
      size: stat.size,
      mtimeMs: stat.mtimeMs,
      kind: "srt",
      streamOrExt: "srt",
    });
    const cached = await readCache(file);
    if (cached) return new NextResponse(new Uint8Array(cached), { headers: VTT_HEADERS });

    let buf: Buffer;
    try {
      buf = await fs.readFile(abs);
    } catch {
      return NextResponse.json({ error: "Read failed" }, { status: 500 });
    }
    // decodeSubtitleBuffer auto-detects UTF-8 / UTF-16 / shift_jis /
    // gb18030 / big5 — a bare `toString("utf8")` mojibakes legacy CN
    // and JP fansub SRTs.
    const raw = decodeSubtitleBuffer(buf);
    const vtt = srtToVtt(raw);
    try {
      await writeCache(file, vtt);
    } catch {
      // Cache miss + failed write isn't fatal; still serve the conversion.
    }
    return new NextResponse(vtt, { headers: VTT_HEADERS });
  }

  if (ext === ".ass" || ext === ".ssa") {
    const file = cachePath({
      abs,
      size: stat.size,
      mtimeMs: stat.mtimeMs,
      kind: ext === ".ass" ? "ass" : "ssa",
      streamOrExt: ext.slice(1),
    });
    const cached = await readCache(file);
    if (cached) return new NextResponse(new Uint8Array(cached), { headers: VTT_HEADERS });
    let buf;
    try {
      buf = await ffmpegToVtt(["-i", abs, "-map", "0:s:0", "-c:s", "webvtt", "-f", "webvtt", "pipe:1"], req.signal);
    } catch {
      return NextResponse.json({ error: "Subtitle conversion failed" }, { status: 500 });
    }
    if (buf.length === 0) return new NextResponse(null, { status: 204 });
    try { await writeCache(file, buf); } catch { /* ignore */ }
    return new NextResponse(new Uint8Array(buf), { headers: VTT_HEADERS });
  }

  return NextResponse.json({ error: "Unsupported subtitle extension" }, { status: 415 });
}

async function handleEmbedded(
  req: NextRequest,
  ctx: { params: Promise<{ code: string }> },
  src: string,
): Promise<NextResponse> {
  const streamIdx = Number.parseInt(src.slice("emb:".length), 10);
  if (!Number.isFinite(streamIdx) || streamIdx < 0) {
    return NextResponse.json({ error: "Invalid stream index" }, { status: 400 });
  }
  const partParam = req.nextUrl.searchParams.get("part");
  const partIdx = partParam == null ? 0 : Number.parseInt(partParam, 10);
  if (!Number.isFinite(partIdx) || partIdx < 0) {
    return NextResponse.json({ error: "Invalid part index" }, { status: 400 });
  }
  const { code } = await ctx.params;
  const decoded = decodeURIComponent(code);
  const variant = findVideosForCode(decoded)[partIdx];
  if (!variant) {
    return NextResponse.json({ error: "Video not found" }, { status: 404 });
  }
  // Re-probe to validate the requested stream is real and text-based.
  // Cheap (sub-100ms) and avoids serving image-based subtitles that
  // would render as garbled text or hang ffmpeg.
  const streams = await runFfprobeSubtitles(variant.abs);
  const target = streams.find((s) => s.index === streamIdx);
  if (!target) {
    return NextResponse.json({ error: "Stream not found" }, { status: 404 });
  }
  if (target.isImageBased) {
    return NextResponse.json({ error: "Image-based subtitles not supported" }, { status: 415 });
  }
  if (!target.isTextBased) {
    return NextResponse.json({ error: "Subtitle codec not supported" }, { status: 415 });
  }

  let stat;
  try {
    stat = await fs.stat(variant.abs);
  } catch {
    return NextResponse.json({ error: "Video not readable" }, { status: 404 });
  }
  const file = cachePath({
    abs: variant.abs,
    size: stat.size,
    mtimeMs: stat.mtimeMs,
    kind: "embedded",
    streamOrExt: streamIdx,
  });
  const cached = await readCache(file);
  if (cached) return new NextResponse(new Uint8Array(cached), { headers: VTT_HEADERS });

  let buf: Buffer;
  try {
    buf = await ffmpegToVtt([
      "-i", variant.abs,
      "-map", `0:s:${streamIdx}`,
      "-c:s", "webvtt",
      "-f", "webvtt",
      "pipe:1",
    ], req.signal);
  } catch {
    return NextResponse.json({ error: "Subtitle extraction failed" }, { status: 500 });
  }
  if (buf.length === 0) return new NextResponse(null, { status: 204 });
  try { await writeCache(file, buf); } catch { /* ignore */ }
  return new NextResponse(new Uint8Array(buf), { headers: VTT_HEADERS });
}

const FFMPEG_TIMEOUT_MS = 15_000;

function ffmpegToVtt(args: string[], signal?: AbortSignal): Promise<Buffer> {
  return new Promise((resolve, reject) => {
    const proc = spawn("ffmpeg", ["-hide_banner", "-loglevel", "error", ...args]);
    const chunks: Buffer[] = [];
    let err = "";
    let settled = false;
    const settle = (fn: () => void) => {
      if (settled) return;
      settled = true;
      clearTimeout(t);
      if (signal && onAbort) signal.removeEventListener("abort", onAbort);
      fn();
    };
    const t = setTimeout(() => {
      try { proc.kill("SIGKILL"); } catch {}
      settle(() => reject(new Error("ffmpeg timed out")));
    }, FFMPEG_TIMEOUT_MS);
    // Tear down the subprocess on client disconnect so a 15-second
    // ghost ffmpeg doesn't keep CPU after the user closes the modal.
    const onAbort = signal
      ? () => {
          try { proc.kill("SIGKILL"); } catch {}
          settle(() => reject(new Error("client aborted")));
        }
      : null;
    if (signal && onAbort) {
      if (signal.aborted) onAbort();
      else signal.addEventListener("abort", onAbort, { once: true });
    }
    proc.stdout?.on("data", (d: Buffer) => { chunks.push(d); });
    proc.stderr?.on("data", (d) => { err += d.toString(); });
    proc.on("error", (e) => settle(() => reject(e)));
    proc.on("close", (code) => {
      settle(() => {
        if (code !== 0) { reject(new Error(err.trim() || `ffmpeg exited ${code}`)); return; }
        resolve(Buffer.concat(chunks));
      });
    });
  });
}