/**
 * Turns a digest off from the link in its email, without signing in. Mail
 * clients post here for a one-click unsubscribe (RFC 8058), and so does the
 * client's `/unsubscribe` page.
 *
 * - `POST /api/unsubscribe?token=` — public, with a digest's unsubscribe
 *   token. Turns that digest off and answers its cadence.
 * - `POST /api/users/unsubscribe?token=` — the same, at its v3 path, which the
 *   `List-Unsubscribe` header of every digest sent before v4 names. Those
 *   tokens never expire, so this path stays for good.
 *
 * @module
 */

import { Router, type RouterMiddleware } from "@oak/oak";

import { type APIResponse } from "../../shared/api.ts";
import { APIException } from "../lib/api-exception.ts";
import { DIGEST_SETTING, type DigestCadence } from "../../shared/settings.ts";
import { verifyUnsubscribeToken } from "../lib/jwt.ts";
import { getUserById } from "../services/user-service.ts";
import { updateSettings } from "../services/settings-service.ts";

/**
 * Mounted by `api/main.ts` behind the error, Open Graph and CORS middleware.
 * An `APIException` thrown by a handler becomes the JSON error response there.
 */
const router: Router = new Router();

// The body is ignored: a mail client's one-click post sends a form saying
// "List-Unsubscribe=One-Click", the client's page sends nothing.
const unsubscribe: RouterMiddleware<string> = async (ctx) => {
  const token = ctx.request.url.searchParams.get("token") ?? "";
  const payload = await verifyUnsubscribeToken(token);
  if (!payload) throw new APIException(400, "Invalid unsubscribe link");
  // Throws a 404 once the account is gone.
  getUserById(payload.userId);
  updateSettings(payload.userId, { [DIGEST_SETTING[payload.cadence]]: false });
  const responseBody: APIResponse<{ cadence: DigestCadence }> = {
    success: true,
    data: { cadence: payload.cadence },
  };
  ctx.response.body = responseBody;
};

router.post("/api/unsubscribe", unsubscribe);
router.post("/api/users/unsubscribe", unsubscribe);

export default router;