/**
 * Callback for a DTMF digit or sequence match.
 * @param arg The digit (for {@link DTMFHandlerImpl.onDigit}) or sequence (for
 * {@link DTMFHandlerImpl.onSequence}) that matched.
 */
export type DTMFCallback = (arg: string) => void | Promise<void> | unknown;
/** Event topic on which DTMF digits are delivered. */
export declare const DTMF_EVENT_TOPIC = "dtmf_received";
/** Maximum number of recent digits retained for sequence matching. */
export declare const SEQUENCE_BUFFER_MAX = 32;
declare class DTMFHandlerImpl {
    private _handlers;
    private _sequenceBuffer;
    constructor(_opts?: Record<string, any>);
    /** Register `callback` to fire each time the given single `digit` is received. */
    onDigit(digit: string, callback: DTMFCallback): void;
    /** Register `callback` to fire when the recent digit stream ends with `sequence`. */
    onSequence(sequence: string, callback: DTMFCallback): void;
    _dispatch(digit: string): void;
    private static _invoke;
}
/**
 * Routes received DTMF (touch-tone) input to callbacks registered per digit
 * ({@link DTMFHandlerImpl.onDigit}) or per sequence ({@link DTMFHandlerImpl.onSequence}).
 */
export type DTMFHandler = DTMFHandlerImpl;
/** Create a {@link DTMFHandler}. */
export declare const DTMFHandler: (_opts?: Record<string, any>) => DTMFHandler;
export {};