import type { LoaderFunctionArgs } from "react-router";

type CacheEntry = { data: ArrayBuffer; contentType: string; expiresAt: number };
const cache = new Map<string, CacheEntry>();
const CACHE_TTL_MS = 24 * 60 * 60 * 1000;
const MAX_CACHE_ENTRIES = 200;

const PRIVATE_IP_RE =
  /^(127\.|10\.|172\.(1[6-9]|2\d|3[01])\.|192\.168\.|::1$|fd[0-9a-f]{2}:)/i;

function isPrivateHost(hostname: string): boolean {
  return PRIVATE_IP_RE.test(hostname) || hostname === "localhost";
}

function resolveContentType(declared: string, data: ArrayBuffer): string | null {
  if (declared.startsWith("image/")) return declared;
  if (declared.startsWith("application/octet-stream") || declared === "") {
    const b = new Uint8Array(data, 0, 12);
    if (b[0] === 0xff && b[1] === 0xd8 && b[2] === 0xff) return "image/jpeg";
    if (b[0] === 0x89 && b[1] === 0x50 && b[2] === 0x4e && b[3] === 0x47) return "image/png";
    if (b[0] === 0x47 && b[1] === 0x49 && b[2] === 0x46) return "image/gif";
    if (b[0] === 0x52 && b[1] === 0x49 && b[2] === 0x46 && b[3] === 0x46 &&
        b[8] === 0x57 && b[9] === 0x45 && b[10] === 0x42 && b[11] === 0x50) return "image/webp";
  }
  return null;
}

export async function loader({ request }: LoaderFunctionArgs) {
  const raw = new URL(request.url).searchParams.get("url");
  if (!raw) return new Response("Missing url", { status: 400 });

  let parsed: URL;
  try {
    parsed = new URL(raw);
  } catch {
    return new Response("Invalid url", { status: 400 });
  }

  if (parsed.protocol !== "http:" && parsed.protocol !== "https:") {
    return new Response("Invalid protocol", { status: 400 });
  }
  if (isPrivateHost(parsed.hostname)) {
    return new Response("Forbidden", { status: 403 });
  }

  const now = Date.now();
  const cached = cache.get(raw);
  if (cached && cached.expiresAt > now) {
    return new Response(cached.data.slice(0), {
      headers: {
        "Content-Type": cached.contentType,
        "Cache-Control": "public, max-age=86400",
      },
    });
  }

  let res: Response;
  try {
    res = await fetch(raw, {
      headers: { "User-Agent": "Tokyo-Livehouse-Events/1.0" },
      signal: AbortSignal.timeout(10_000),
    });
  } catch {
    return new Response("Upstream unreachable", { status: 502 });
  }

  if (!res.ok) return new Response("Upstream error", { status: 502 });

  const contentType = res.headers.get("content-type") ?? "";
  const data = await res.arrayBuffer();

  const resolvedType = resolveContentType(contentType, data);
  if (!resolvedType) {
    return new Response("Not an image", { status: 400 });
  }

  if (cache.size >= MAX_CACHE_ENTRIES) {
    cache.delete(cache.keys().next().value!);
  }
  cache.set(raw, { data, contentType: resolvedType, expiresAt: now + CACHE_TTL_MS });

  return new Response(data.slice(0), {
    headers: {
      "Content-Type": resolvedType,
      "Cache-Control": "public, max-age=86400",
      "X-Content-Type-Options": "nosniff",
    },
  });
}