import { IStorageEventData } from '../../types.ts';
/**
 * Callback function type for event listeners.
 * @template T - The type of data passed to the callback
 */
export type Callback<T = unknown> = (event: IStorageEventData<T>) => void;
export declare class Observer {
    private static eventRegistry;
    private static getRegistry;
    /**
     * Adds an event listener for the specified event.
     */
    static on<T = unknown>(event: string, callback: Callback<T>): void;
    /**
     * Adds a one-time event listener that fires at most once and is then removed.
     */
    static once<T = unknown>(event: string, callback: Callback<T>): void;
    /**
     * Removes a specific listener (from both regular and once registries).
     */
    static off<T = unknown>(event: string, callback: Callback<T>): void;
    /**
     * Emits an event to all registered listeners.
     *
     * Guarantees:
     *  - A throwing listener never blocks other listeners.
     *  - A throwing listener never propagates the error into the caller of `set/remove/clear`.
     *  - Mutating listener sets during emission is safe (iteration uses a snapshot).
     *  - A recursive `emit` from inside a `once` callback will NOT re-fire the same once-listeners.
     */
    static emit<T = unknown>(event: string, data: IStorageEventData<T>): void;
    /**
     * Removes every listener for every event on this class.
     */
    static removeAllListeners(): void;
    /**
     * Removes every listener for a single event.
     */
    static removeListener(event: string): void;
    /**
     * Total number of listeners (regular + once) for an event.
     */
    static listenerCount(event: string): number;
    /**
     * All event names with at least one listener.
     */
    static eventNames(): string[];
}