/**
 * Keeps the instances an admin trusts or blocks for federated sign-in
 * (`federation_peers`). Users of a trusted instance sign in here directly,
 * those of a blocked one never do, and an instance on neither list is invite
 * only. `federation-service.ts` reads it at each sign-in, `/manage` edits it
 * through `routes/federation.ts`, and the login page offers the trusted ones.
 *
 * @module
 */

import { APIException } from "../lib/api-exception.ts";
import { db } from "../db/connection.ts";
import { PUBLIC_URL } from "../config.ts";
import {
  type FederationPeer,
  instanceHost,
  isPeerStatus,
  parseInstance,
  type PeerStatus,
} from "../../shared/federation.ts";
import { fetchMetadata } from "../remote/gerbeur-instance.ts";
import { closeUserSockets } from "./ws-service.ts";

interface PeerRow {
  issuer: string;
  status: string;
  name: string | null;
  created_at: string;
}

/** Converts a row to a {@link FederationPeer}. */
function rowToPeer(row: PeerRow): FederationPeer {
  return {
    issuer: row.issuer,
    host: instanceHost(row.issuer),
    name: row.name,
    status: isPeerStatus(row.status) ? row.status : "blocked",
    createdAt: new Date(row.created_at),
  };
}

/**
 * Returns what an admin decided about the instance at `issuer`, or null when
 * it is on neither list.
 */
export function getPeerStatus(issuer: string): PeerStatus | null {
  const row = db.prepare(
    `SELECT status FROM federation_peers WHERE issuer = ?;`,
  ).get(issuer) as { status: string } | undefined;
  return row && isPeerStatus(row.status) ? row.status : null;
}

/**
 * Returns the instances on the lists, by name: every one for `/manage`, or
 * only the trusted ones, which the login page offers.
 */
export function listPeers(trustedOnly: boolean): FederationPeer[] {
  const rows = db.prepare(
    `SELECT issuer, status, name, created_at FROM federation_peers
      ${trustedOnly ? "WHERE status = 'trusted'" : ""}
      ORDER BY lower(coalesce(name, issuer));`,
  ).all() as unknown as PeerRow[];
  return rows.map(rowToPeer);
}

/**
 * Puts the instance `instance` names on the list of `status`, for `/manage`,
 * and returns it. It must answer as a gerbeur instance, whose name is kept.
 * Blocking one ends the sessions of its users here at once: their tokens stop
 * counting by `getSessionState`, and this closes their sockets.
 *
 * @throws {APIException} 400 when `instance` names no instance, or this one,
 * 502 when it doesn't answer as a gerbeur instance.
 */
export async function setPeer(
  instance: string,
  status: PeerStatus,
): Promise<FederationPeer> {
  const issuer = parseInstance(instance);
  if (!issuer) throw new APIException(400, "Not an instance's address");
  if (issuer === PUBLIC_URL) {
    throw new APIException(400, "That is this instance");
  }
  let name: string;
  try {
    name = (await fetchMetadata(issuer)).gerbeur_site_name;
  } catch (err) {
    console.error(`[federation] ${issuer} can't be added:`, err);
    throw new APIException(502, "That address doesn't answer as a gerbeur");
  }
  db.prepare(
    `INSERT INTO federation_peers (issuer, status, name, created_at)
       VALUES (?, ?, ?, ?)
     ON CONFLICT (issuer) DO UPDATE SET status = excluded.status, name = excluded.name;`,
  ).run(issuer, status, name, new Date().toISOString());

  if (status === "blocked") {
    const users = db.prepare(
      `SELECT user_id FROM user_identities WHERE issuer = ?;`,
    ).all(issuer) as { user_id: string }[];
    for (const { user_id } of users) {
      closeUserSockets(user_id, "Instance blocked");
    }
  }

  const row = db.prepare(
    `SELECT issuer, status, name, created_at FROM federation_peers WHERE issuer = ?;`,
  ).get(issuer) as unknown as PeerRow;
  return rowToPeer(row);
}

/**
 * Takes the instance whose host is `host` off the lists, for `/manage`: its
 * users are invite only again, and those already here may sign in again if it
 * was blocked.
 *
 * @throws {APIException} 404 when no listed instance has that host.
 */
export function removePeer(host: string): void {
  const peer = listPeers(false).find((p) => p.host === host.toLowerCase());
  if (!peer) throw new APIException(404, "Instance not found");
  db.prepare(`DELETE FROM federation_peers WHERE issuer = ?;`).run(
    peer.issuer,
  );
}