import { ShareHttpError } from "@/lib/share/http-error";

export type FixedWindowIncrement = (
  key: string,
  expiresInSeconds: number,
) => Promise<number>;

export async function enforceFixedWindowRateLimit({
  key,
  limit,
  windowSeconds,
  increment,
  now = Date.now(),
}: {
  key: string;
  limit: number;
  windowSeconds: number;
  increment: FixedWindowIncrement;
  now?: number;
}) {
  const nowSeconds = Math.floor(now / 1000);
  const window = Math.floor(nowSeconds / windowSeconds);
  const retryAfter = windowSeconds - (nowSeconds % windowSeconds);

  let count: number;
  try {
    count = await increment(
      `erika:share:${key}:${window}`,
      windowSeconds + 1,
    );
  } catch {
    throw new ShareHttpError("Rate limiting is temporarily unavailable", 503);
  }

  if (!Number.isFinite(count)) {
    throw new ShareHttpError("Rate limiting is temporarily unavailable", 503);
  }
  if (count > limit) {
    throw new ShareHttpError("Rate limit exceeded", 429, retryAfter);
  }
}