/**
 * @file SSE Client
 * @description Low-level Server-Sent Events client
 */
/**
 * SSE connection state
 */
export type SSEState = 'connecting' | 'connected' | 'disconnected' | 'reconnecting';
/**
 * SSE message handler
 */
export type SSEMessageHandler = (data: unknown, event?: string) => void;
/**
 * SSE error handler
 */
export type SSEErrorHandler = (error: Event) => void;
/**
 * SSE state change handler
 */
export type SSEStateChangeHandler = (state: SSEState) => void;
/**
 * SSE client configuration
 */
export interface SSEClientConfig {
    url: string;
    withCredentials?: boolean;
    reconnect?: boolean;
    reconnectInterval?: number;
    maxReconnectAttempts?: number;
    eventTypes?: string[];
}
/**
 * SSE client class
 */
export declare class SSEClient {
    private eventSource;
    private config;
    private state;
    private reconnectAttempts;
    private reconnectTimeout;
    private messageHandlers;
    private errorHandlers;
    private stateChangeHandlers;
    /**
     * Store bound event handler references for proper cleanup
     * This fixes a memory leak where createEventHandler() created new functions
     * that couldn't be properly removed with removeEventListener
     */
    private boundEventHandlers;
    constructor(config: SSEClientConfig);
    /**
     * Get current connection state
     */
    getState(): SSEState;
    /**
     * Check if connected
     */
    isConnected(): boolean;
    /**
     * Connect to SSE endpoint
     */
    connect(): void;
    /**
     * Disconnect from SSE endpoint
     */
    disconnect(): void;
    /**
     * Subscribe to messages of a specific event type
     *
     * Note: Uses stored bound handler references for proper cleanup.
     * This prevents memory leaks from orphaned event listeners.
     */
    on(eventType: string, handler: SSEMessageHandler): () => void;
    /**
     * Subscribe to all 'message' events (default)
     */
    onMessage(handler: SSEMessageHandler): () => void;
    /**
     * Subscribe to errors
     */
    onError(handler: SSEErrorHandler): () => void;
    /**
     * Subscribe to state changes
     */
    onStateChange(handler: SSEStateChangeHandler): () => void;
    /**
     * Setup EventSource event listeners
     */
    private setupEventListeners;
    /**
     * Add listener for specific event type
     *
     * Note: Stores bound handler reference for proper cleanup later.
     */
    private addEventTypeListener;
    /**
     * Create event handler for event type
     */
    private createEventHandler;
    /**
     * Handle disconnection
     */
    private handleDisconnect;
    /**
     * Schedule reconnection
     */
    private scheduleReconnect;
    /**
     * Calculate exponential backoff delay
     */
    private calculateBackoff;
    /**
     * Clear reconnect timeout
     */
    private clearReconnectTimeout;
    /**
     * Update and broadcast state
     */
    private setState;
}
/**
 * Create SSE client with default configuration
 */
export declare function createSSEClient(path?: string, config?: Partial<SSEClientConfig>): SSEClient;