cinny/src/app/utils/retention.ts

import { Room } from 'matrix-js-sdk';
import { StateEvent } from '../../types/matrix/room';

// MSC1763 — per-room message retention (`m.room.retention`). `max_lifetime` is a
// duration in milliseconds after which a message is considered expired.
export type RetentionContent = {
  max_lifetime?: number;
};

const DAY_MS = 24 * 60 * 60 * 1000;

// Floor to avoid foot-guns (an admin fat-fingering a tiny value nuking a room).
export const RETENTION_MIN_MS = 10 * 60 * 1000;

export type RetentionPreset = { label: string; ms: number };
export const RETENTION_PRESETS: RetentionPreset[] = [
  { label: 'Off', ms: 0 },
  { label: '1 Day', ms: DAY_MS },
  { label: '1 Week', ms: 7 * DAY_MS },
  { label: '1 Month', ms: 30 * DAY_MS },
];

/**
 * [Gitea #298] A usable retention window, or `undefined`. Anything under
 * RETENTION_MIN_MS is treated as off: a fat-fingered `max_lifetime: 1000` (set
 * from any client by anyone with state power) used to blank every timeline and
 * get opted-in users' messages redacted within a minute.
 */
export const effectiveRetentionMs = (maxLifetime: unknown): number | undefined =>
  typeof maxLifetime === 'number' && Number.isFinite(maxLifetime) && maxLifetime >= RETENTION_MIN_MS
    ? maxLifetime
    : undefined;

/** The room's active retention window in ms, or `undefined` when unset/disabled. */
export const getRoomRetentionMs = (room: Room): number | undefined => {
  const event = room.currentState.getStateEvents(StateEvent.RoomRetention, '');
  return effectiveRetentionMs(event?.getContent<RetentionContent>()?.max_lifetime);
};

/**
 * [Gitea #298] Deletion grace: the auto-delete sweeper ignores a retention
 * policy for this long after it was set, so a mistaken or malicious change can
 * be reverted before anything is permanently redacted. (Hiding expired
 * messages locally is not destructive and applies at once.)
 */
export const RETENTION_DELETE_GRACE_MS = DAY_MS;

export const retentionDeletesAllowed = (policySetAtMs: number, nowMs: number): boolean =>
  nowMs - policySetAtMs >= RETENTION_DELETE_GRACE_MS;

/** When the room's current retention policy was set (its state event's ts). */
export const getRoomRetentionSetAt = (room: Room): number | undefined =>
  room.currentState.getStateEvents(StateEvent.RoomRetention, '')?.getTs();

/** True when an event at `tsMs` has passed the `maxLifetimeMs` retention window. */
export const isExpired = (tsMs: number, maxLifetimeMs: number, nowMs: number): boolean =>
  maxLifetimeMs > 0 && nowMs - tsMs > maxLifetimeMs;