/**
 * Lets users of other gerbeur instances sign in here with their account
 * there, as `federation-service.ts` describes, and lets admins pick the
 * instances to trust or block. The login and register pages start a sign-in,
 * the `/federation/callback` page finishes it, `/manage` edits the peers, and
 * the other instances' servers send their events.
 *
 * - `POST /api/federation/logins` — public. Starts a sign-in with an account
 *   on another instance (`FederationLoginRequest`, with an invite unless it
 *   is trusted), and answers its `/authorize` page to go to. Rate-limited per
 *   instance.
 * - `POST /api/federation/sessions` — public. Finishes it
 *   (`FederationSessionRequest`) and answers the user and their tokens, as a
 *   sign-in does. Each sign-in started finishes once, so the limit on
 *   `/logins` bounds it.
 * - `POST /api/federation/events` — public, server to server. Applies a
 *   home instance's signed event about one of its users (`{ event }`).
 *   Rate-limited per instance; a 4xx tells the sender to give up on the
 *   event, a 429 or a 5xx to try again.
 * - `GET /api/federation/peers` — optional sign-in. Answers the trusted
 *   instances, or every listed one to `federation:manage`.
 * - `PUT /api/federation/peers` — permission `federation:manage`. Trusts or
 *   blocks an instance (`SetPeerRequest`) and answers it; 502 when one to
 *   trust doesn't answer as a gerbeur.
 * - `DELETE /api/federation/peers/:host` — permission `federation:manage`.
 *   Takes an instance off the lists.
 *
 * @module
 */

import { Router } from "@oak/oak";
import type { APIResponse } from "../../shared/api.ts";
import {
  type FederationLoginResponse,
  type FederationPeer,
  parseInstance,
} from "../../shared/federation.ts";
import type { AuthResponse } from "../../shared/user.ts";
import { APIException } from "../lib/api-exception.ts";
import { parseOptionalAuth } from "../lib/auth.ts";
import { issueTokens } from "../lib/jwt.ts";
import { hasPermission } from "../../shared/permissions.ts";
import { type RateLimit, takeToken } from "../lib/rate-limit.ts";
import {
  type AuthContext,
  authMiddleware,
  requirePermission,
} from "../middleware/auth.ts";
import { toSelfUser } from "../model/user.ts";
import {
  isFederationLoginRequest,
  isFederationSessionRequest,
  isSetPeerRequest,
} from "../validators/federation.ts";
import {
  completeLogin,
  receiveEvent,
  startLogin,
} from "../services/federation-service.ts";
import {
  listPeers,
  removePeer,
  setPeer,
} from "../services/federation-peer-service.ts";
import { getUserById } from "../services/user-service.ts";
import { fieldOf } from "../validators/user.ts";

/**
 * Allows a burst of 30 sign-ins per instance, then one every 2 seconds, so
 * that nobody makes this instance hammer another.
 */
const LOGIN_LIMIT: RateLimit = { capacity: 30, refill: 1 / 2 };

/**
 * 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({ prefix: "/api/federation" });

router.post("/logins", async (ctx) => {
  const body: unknown = await ctx.request.body.json();
  if (!isFederationLoginRequest(body)) {
    throw new APIException(400, "Invalid request");
  }
  if (!takeToken(`federation:${parseInstance(body.instance)}`, LOGIN_LIMIT)) {
    throw new APIException(429, "Too many sign-ins — try again in a minute");
  }
  const responseBody: APIResponse<FederationLoginResponse> = {
    success: true,
    data: { authorizeUrl: await startLogin(body) },
  };
  ctx.response.body = responseBody;
});

router.post("/sessions", async (ctx) => {
  const body: unknown = await ctx.request.body.json();
  if (!isFederationSessionRequest(body)) {
    throw new APIException(400, "Invalid request");
  }
  const user = await completeLogin(body);
  const responseBody: APIResponse<AuthResponse> = {
    success: true,
    data: { ...await issueTokens(user), user: toSelfUser(user) },
  };
  ctx.response.body = responseBody;
});

router.post("/events", async (ctx) => {
  const event = fieldOf(await ctx.request.body.json(), "event");
  if (typeof event !== "string") throw new APIException(400, "Invalid event");
  await receiveEvent(event);
  ctx.response.status = 204;
});

router.get("/peers", async (ctx) => {
  const userId = await parseOptionalAuth(ctx);
  const all = !!userId &&
    hasPermission(getUserById(userId).role, "federation:manage");
  const responseBody: APIResponse<FederationPeer[]> = {
    success: true,
    data: listPeers(!all),
  };
  ctx.response.body = responseBody;
});

router.put(
  "/peers",
  authMiddleware,
  requirePermission("federation:manage"),
  async (ctx: AuthContext) => {
    const body: unknown = await ctx.request.body.json();
    if (!isSetPeerRequest(body)) throw new APIException(400, "Invalid request");
    const responseBody: APIResponse<FederationPeer> = {
      success: true,
      data: await setPeer(body.instance, body.status),
    };
    ctx.response.body = responseBody;
  },
);

router.delete(
  "/peers/:host",
  authMiddleware,
  requirePermission("federation:manage"),
  (ctx: AuthContext<"/peers/:host">) => {
    removePeer(ctx.params.host);
    const responseBody: APIResponse<null> = { success: true, data: null };
    ctx.response.body = responseBody;
  },
);

export default router;