import type { Middleware } from "../core/server.ts";
import { merge } from "../core/utils/object.ts";

export interface Options {
  /** The path to the shutdown page */
  page?: string;

  /**
   * The time in seconds to retry after.
   * @default 60 * 60 * 24 (24 hours)
   */
  retryAfter?: number;
}

export const defaults = {
  page: "/503.html",
  retryAfter: 60 * 60 * 24, // 24 hours
} satisfies Options;

export function shutdown(
  userOptions?: Options,
): Middleware {
  const options = merge(defaults, userOptions);

  return async (request, next) => {
    if (!isHtml(request)) {
      return await next(request);
    }

    const url = new URL(options.page, request.url).toString();
    const response = await next(new Request(url, request));

    const { body, headers } = response;
    headers.set("Retry-After", options.retryAfter.toString());

    return new Response(body, {
      status: 503,
      statusText: "Service Unavailable",
      headers,
    });
  };
}

function isHtml(request: Request) {
  const accept = request.headers.get("accept");
  return accept && accept.includes("text/html");
}

export default shutdown;