cinny/src/app/utils/settingsSync.ts

import { Settings } from '../state/settings';

/**
 * [Gitea #104] Settings sync — pure helpers.
 *
 * Lotus settings live in `localStorage` per device. A syncable subset is
 * mirrored to the account-data event `io.lotus.settings` on the user's own
 * homeserver so a second device picks it up. Everything device-bound stays
 * local (see DEVICE_LOCAL_KEYS). Conflicts are last-write-wins on the
 * `updatedAt` stamp inside the event; a device that applied a remote snapshot
 * remembers it so the resulting local change is not echoed straight back.
 */

export const SETTINGS_SYNC_EVENT = 'io.lotus.settings';
export const SETTINGS_SYNC_VERSION = 1;

export type SyncedSettingsContent = {
  version: number;
  updatedAt: number;
  settings: Partial<Settings>;
};

// Keys that describe THIS device (display, hardware, bandwidth, CPU budget,
// transient UI state, per-device permissions) rather than the user's
// preferences. Never written to, or read from, the synced event. The sync
// toggle itself is local too, so turning it off on one device is not undone by
// another.
export const DEVICE_LOCAL_KEYS: ReadonlySet<keyof Settings> = new Set<keyof Settings>([
  'settingsSync',
  'globalCallHotkeys',
  'pageZoom',
  'mediaAutoLoad',
  'pauseAnimations',
  'glassmorphismSidebar',
  'isPeopleDrawer',
  'memberSortFilterIndex',
  'presenceStatus',
  'showNotifications',
  'developerTools',
  'pttMode',
  'callNoiseSuppression',
  'callDenoiseModel',
  'callDenoiseNativeNS',
  'callDenoiseGate',
  'callDenoiseGateThreshold',
  'callAudioBitrate',
  'screenshareBitrate',
  'screenshareFramerate',
  'ringtoneVolume',
  'soundboardVolume',
  'cameraOnJoin',
]);

/** The subset of `settings` that is synced (deep-copied so callers can't alias). */
export const pickSyncable = (settings: Settings): Partial<Settings> => {
  const out: Partial<Settings> = {};
  (Object.keys(settings) as (keyof Settings)[]).forEach((key) => {
    if (DEVICE_LOCAL_KEYS.has(key)) return;
    const value = settings[key];
    if (value === undefined) return;
    (out as Record<string, unknown>)[key] =
      typeof value === 'object' && value !== null ? JSON.parse(JSON.stringify(value)) : value;
  });
  return out;
};

/** Structural equality of two syncable subsets (key order independent). */
export const syncableEqual = (a: Partial<Settings>, b: Partial<Settings>): boolean => {
  const ka = Object.keys(a).sort();
  const kb = Object.keys(b).sort();
  if (ka.length !== kb.length) return false;
  for (let i = 0; i < ka.length; i += 1) {
    if (ka[i] !== kb[i]) return false;
    const va = (a as Record<string, unknown>)[ka[i]];
    const vb = (b as Record<string, unknown>)[kb[i]];
    if (JSON.stringify(va) !== JSON.stringify(vb)) return false;
  }
  return true;
};

/** Type guard for what comes back from account data (any client, any version). */
export const isSyncedSettingsContent = (content: unknown): content is SyncedSettingsContent => {
  if (typeof content !== 'object' || content === null) return false;
  const c = content as Record<string, unknown>;
  return (
    typeof c.version === 'number' &&
    typeof c.updatedAt === 'number' &&
    Number.isFinite(c.updatedAt) &&
    typeof c.settings === 'object' &&
    c.settings !== null &&
    !Array.isArray(c.settings)
  );
};

/**
 * Overlay a remote snapshot onto the local settings. Only syncable keys the
 * local schema knows about are taken (so a newer client's extra keys, or a
 * device-local key smuggled in by a buggy writer, are ignored). Values are
 * copied verbatim; the caller runs the result through the normal
 * `getSettings()` coercion by persisting it, which is what validates enums.
 */
export const mergeRemoteSettings = (local: Settings, remote: SyncedSettingsContent): Settings => {
  const merged: Settings = { ...local };
  (Object.keys(remote.settings) as (keyof Settings)[]).forEach((key) => {
    if (DEVICE_LOCAL_KEYS.has(key)) return;
    if (!(key in local)) return;
    const value = remote.settings[key];
    if (value === undefined) return;
    // Shape guard: a value of a different JS type than this build stores for
    // the key (e.g. a renamed enum that became an object) is skipped; enum
    // *values* are validated by getSettings() coercion on the next load.
    const current = local[key];
    if (current !== undefined && current !== null && typeof value !== typeof current) return;
    if (Array.isArray(current) !== Array.isArray(value)) return;
    (merged as unknown as Record<string, unknown>)[key] = value;
  });
  return merged;
};

export const buildSyncedContent = (
  settings: Settings,
  updatedAt: number = Date.now(),
): SyncedSettingsContent => ({
  version: SETTINGS_SYNC_VERSION,
  updatedAt,
  settings: pickSyncable(settings),
});

/**
 * Should a remote snapshot be applied over what this device last synced?
 * `lastSyncedAt` is the stamp of the snapshot this device last pushed or
 * applied; anything older or equal is our own echo (or a stale write that lost
 * the race) and is ignored.
 */
export const shouldApplyRemote = (
  remote: SyncedSettingsContent,
  lastSyncedAt: number | null,
): boolean => lastSyncedAt === null || remote.updatedAt > lastSyncedAt;