/** How many recent samples each source keeps. */
export declare const SERVER_CLOCK_WINDOW = 9;
/** Samples this close to the median agree with it. Wider than the `Date` header's 1 s resolution plus latency. */
export declare const SERVER_CLOCK_AGREEMENT_MS = 2000;
export type ServerClockSource = 'room' | 'http';
export declare class ServerClock {
    private readonly deviceNow;
    private readonly windows;
    private readonly lastHeard;
    private heard;
    constructor(deviceNow?: () => number);
    /** A server timestamp (epoch ms) received at `receivedAt` (device epoch ms; default: now). Anything unusable is ignored. */
    observe(serverMs: unknown, source: ServerClockSource, receivedAt?: number): void;
    /**
     * An HTTP `Date` header value (null when the browser did not expose it). The header is truncated to the
     * second, so the middle of that second is taken.
     */
    observeHttpDate(header: string | null | undefined, receivedAt?: number): void;
    /** Server time minus device time, in ms, or null when no source is trusted yet. */
    offsetMs(): number | null;
    /** The platform's time now (epoch ms): the device clock corrected by the trusted offset, or the device clock alone. */
    now(): number;
    /** Whether `expiresAt` (epoch ms) has passed by the platform's clock. An unreadable expiry (NaN) never has. */
    hasPassed(expiresAt: number): boolean;
}