import { NextRequest, NextResponse } from "next/server";
import path from "node:path";
import { findVideosForCode, getVideoIndex, rescanVideoIndex } from "@/lib/video";
import { assertLocalRequest } from "@/lib/api/localOnly";
import {
  walkSubtitles,
  detectLanguageFromName,
  normalizeLanguageTag,
  languageDisplay,
  stemOf,
  type LangIso,
} from "@/lib/video/subtitles";
import { runFfprobeSubtitles } from "@/lib/video/metadata";
import { getAppSetting } from "@/lib/db/appSettings";
import { listManualSubtitlesForVariant } from "@/lib/video/manualSubtitles";
import fs from "node:fs";

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

/** Sidecar (external file) subtitle source. */
interface SidecarOut {
  /** Stable client-side id; encodes the abs path so the track endpoint
   *  can resolve it. */
  id: string;
  abs: string;
  filename: string;
  ext: string; // ".srt" | ".vtt" | ".ass" | ".ssa"
  language: LangIso | null;
  label: string;
  origin: "same-folder" | "library" | "manual";
}

/** Embedded-stream subtitle source (filled in once ffprobe is wired up
 *  in phase 2). */
interface EmbeddedOut {
  id: string;
  streamIndex: number;
  codec: string;
  language: LangIso | null;
  label: string;
  renderable: boolean;
}

function formatCodecLabel(codec: string): string | null {
  switch (codec) {
    case "subrip": return "SRT";
    case "ass": return "ASS";
    case "ssa": return "SSA";
    case "mov_text": return "mov_text";
    case "webvtt": return "VTT";
    case "hdmv_pgs_subtitle": return "PGS";
    case "dvd_subtitle": return "DVDSub";
    case "dvb_subtitle": return "DVBSub";
    default: return codec ? codec.toUpperCase() : null;
  }
}

function encodeSideId(abs: string): string {
  return `side:${Buffer.from(abs, "utf8").toString("base64url")}`;
}

/** Filter walkSubtitles results to entries that look like they belong
 *  to this specific video — stem prefix is the strong signal; code
 *  substring is the fallback. Both case-insensitive. */
function matchesVideo(filename: string, stem: string, code: string): boolean {
  const lowerName = filename.toLowerCase();
  const lowerStem = stem.toLowerCase();
  const lowerCode = code.toLowerCase();
  if (lowerName.startsWith(lowerStem + ".")) return true;
  if (lowerName === lowerStem) return true;
  return lowerName.includes(lowerCode);
}

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 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 });
  }

  let files = findVideosForCode(decoded);
  if (files.length === 0) {
    // Cold-boot path: VideoIndexProvider may not have triggered the
    // initial scan yet. Build it once so the picker doesn't appear
    // empty on first modal open after server start.
    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);
    }
  }
  const variant = files[partIdx];
  if (!variant) {
    return NextResponse.json({ embedded: [], sidecar: [] });
  }

  const variantStem = stemOf(variant.filename);
  const dir = path.dirname(variant.abs);

  // Phase 1: same-folder sidecars only. Embedded streams + library scan
  // are added in later phases via additive concat into these arrays.
  const sidecar: SidecarOut[] = [];

  const seen = new Set<string>();
  const pushEntry = (
    entry: { abs: string; filename: string },
    origin: "same-folder" | "library",
  ) => {
    if (seen.has(entry.abs)) return;
    if (!matchesVideo(entry.filename, variantStem, decoded)) return;
    seen.add(entry.abs);
    const detected = detectLanguageFromName(entry.filename);
    const ext = path.extname(entry.filename).toLowerCase();
    sidecar.push({
      id: encodeSideId(entry.abs),
      abs: entry.abs,
      filename: entry.filename,
      ext,
      language: detected.lang,
      label: detected.label,
      origin,
    });
  };

  try {
    for (const entry of await walkSubtitles(dir, 1)) pushEntry(entry, "same-folder");
  } catch { /* ignore */ }

  // Library scan: persistent extra paths from settings. Slightly deeper
  // walk because users typically point these at organized hierarchies.
  const extraPaths = (getAppSetting("subtitleExtraPaths") ?? []).filter(Boolean);
  for (const root of extraPaths) {
    try {
      for (const entry of await walkSubtitles(root, 3)) pushEntry(entry, "library");
    } catch { /* missing or unreadable root */ }
  }

  // Implicit always-on root: data/generated-subtitles/<code>/ catches
  // WhisperJAV-produced .srt when the video folder isn't writable.
  const generatedDir = path.join(process.cwd(), "data", "generated-subtitles", decoded);
  try {
    for (const entry of await walkSubtitles(generatedDir, 1)) pushEntry(entry, "library");
  } catch { /* nothing generated yet */ }

  // Manually attached files via Browse... in the player. Persisted
  // across sessions; only included when the file still exists on disk.
  for (const m of listManualSubtitlesForVariant(decoded, partIdx)) {
    if (seen.has(m.absPath)) continue;
    if (!fs.existsSync(m.absPath)) continue;
    const filename = path.basename(m.absPath);
    if (!filename) continue;
    const detected = detectLanguageFromName(filename);
    const ext = path.extname(filename).toLowerCase();
    seen.add(m.absPath);
    sidecar.push({
      id: encodeSideId(m.absPath),
      abs: m.absPath,
      filename,
      ext,
      language: detected.lang,
      label: detected.label,
      origin: "manual",
    });
  }

  // Stable order: same-folder before library, then by language priority
  // (EN, CN, JP, Unknown), then by filename.
  const langRank: Record<string, number> = { eng: 0, zho: 1, jpn: 2 };
  sidecar.sort((a, b) => {
    if (a.origin !== b.origin) return a.origin === "same-folder" ? -1 : 1;
    const ra = a.language ? (langRank[a.language] ?? 9) : 9;
    const rb = b.language ? (langRank[b.language] ?? 9) : 9;
    if (ra !== rb) return ra - rb;
    return a.filename.localeCompare(b.filename);
  });

  const embedded: EmbeddedOut[] = [];
  let streams: Awaited<ReturnType<typeof runFfprobeSubtitles>> = [];
  try {
    streams = await runFfprobeSubtitles(variant.abs);
  } catch {
    streams = [];
  }
  for (const s of streams) {
    const iso = normalizeLanguageTag(s.language);
    const codecLabel = formatCodecLabel(s.codec);
    const trailing: string[] = [];
    if (s.title) trailing.push(s.title);
    if (codecLabel) trailing.push(codecLabel);
    const base = iso ? languageDisplay(iso) : (s.title ?? "Unknown");
    const label = trailing.length > 0 && !iso
      ? `${base}${codecLabel ? ` (${codecLabel})` : ""}`
      : codecLabel
        ? `${base} (${codecLabel})`
        : base;
    embedded.push({
      id: `emb:${s.index}`,
      streamIndex: s.index,
      codec: s.codec,
      language: iso,
      label,
      renderable: s.isTextBased,
    });
  }

  return NextResponse.json(
    { embedded, sidecar },
    { headers: { "Cache-Control": "no-store" } },
  );
}