import { Flashcard } from '../types.js';
/**
 * Updates the `dueDate` and `interval` of a flashcard based on the given difficulty.
 *
 * The function adjusts the interval of the card, adding a value based on the difficulty.
 * If the difficulty is 0, the interval is reset to 0. Otherwise, the interval accumulates
 * over time. The due date is updated to reflect the new interval in minutes.
 *
 * @param {Flashcard} card - The flashcard to update. It should have `dueDate` and `interval` properties.
 * @param {number} difficulty - The difficulty level of the card, ranging from 0 (hardest) to 3 (easiest).
 *
 * @throws {Error} Throws an error if the difficulty level is not between 0 and 3.
 *
 * @example
 * const card = { dueDate: Date.now(), interval: 5 };
 * fenestralLacuna(card, 2);
 * // Updates card's interval to 7 (5 + 2) and adjusts dueDate accordingly.
 */
export declare function fenestralLacuna(card: Flashcard, difficulty: number): void;