malice

import { get, writable } from 'svelte/store';

import { ApiError, getAccountData, getUrlPreview, setAccountData } from './api';

import { parseLinkPreview } from './types';

import type { LinkPreview } from './types';

const EVENT_TYPE = 'dev.malice.url_previews';

const BACKOFF_MS = 30_000;

const BATCH_MS = 150;

export interface UrlPreviewSettings {

  encrypted_rooms: boolean;

}

const DEFAULT_SETTINGS: UrlPreviewSettings = { encrypted_rooms: false };

export const linkPreviews = writable<Record<string, LinkPreview | null>>({});

export const urlPreviewSettings = writable<UrlPreviewSettings>(DEFAULT_SETTINGS);

const inFlight = new Set<string>();

const landed: Record<string, LinkPreview | null> = {};

let flushTimer: ReturnType<typeof setTimeout> | null = null;

/** Previews resolve one by one after a room opens, and each one landing on its own shifted the timeline again. */

function land(url: string, preview: LinkPreview | null): void {

  landed[url] = preview;

  flushTimer ??= setTimeout(() => {

    flushTimer = null;

    const batch = { ...landed };

    for (const key of Object.keys(landed)) delete landed[key];

    linkPreviews.update((all) => ({ ...all, ...batch }));

  }, BATCH_MS);

}

let backoffUntil = 0;

let refusalLogged = false;

export function requestLinkPreview(roomId: string, url: string): void {

  if (inFlight.has(url) || url in landed || url in get(linkPreviews) || Date.now() < backoffUntil) return;

  inFlight.add(url);

  getUrlPreview(roomId, url)

    .then((raw) => land(url, parseLinkPreview(raw)))

    .catch((e) => {

      if (e instanceof ApiError && e.status === 429) backoffUntil = Date.now() + BACKOFF_MS;

      else if (e instanceof ApiError && e.status === 403) {

        land(url, null);

        if (!refusalLogged) console.warn('The homeserver refused a link preview', e.message);

        refusalLogged = true;

      }

    })

    .finally(() => inFlight.delete(url));

}

function parseSettings(raw: unknown): UrlPreviewSettings {

  if (typeof raw !== 'object' || raw === null) return DEFAULT_SETTINGS;

  return { encrypted_rooms: (raw as Record<string, unknown>)['encrypted_rooms'] === true };

}

export async function loadUrlPreviewSettings(): Promise<void> {

  try {

    urlPreviewSettings.set(parseSettings(await getAccountData(EVENT_TYPE)));

  } catch {

    urlPreviewSettings.set(DEFAULT_SETTINGS);

  }

}

export async function saveUrlPreviewSettings(settings: UrlPreviewSettings): Promise<void> {

  await setAccountData(EVENT_TYPE, { encrypted_rooms: settings.encrypted_rooms });

  urlPreviewSettings.set(settings);

}

export function resetLinkPreviews(): void {

  linkPreviews.set({});

  urlPreviewSettings.set(DEFAULT_SETTINGS);

  inFlight.clear();

  if (flushTimer) clearTimeout(flushTimer);

  flushTimer = null;

  for (const key of Object.keys(landed)) delete landed[key];

  backoffUntil = 0;

}