/**
 * SSE Transport Adapter
 *
 * Server-Sent Events transport for real-time streaming.
 * Uses Web Streams API for compatibility with Next.js/Edge runtime.
 */
import type { StreamMessage, StreamTransportAdapterConfig } from '@plyaz/types/core';
import { BaseTransportAdapter } from '../BaseTransportAdapter';
/**
 * SSETransportAdapter - Server-Sent Events transport
 *
 * Features:
 * - Web Streams API for Edge runtime compatibility
 * - Automatic heartbeat to keep connections alive
 * - Proper SSE formatting with event, id, retry, data fields
 * - Connection cleanup on disconnect
 *
 * @example
 * ```ts
 * const sseAdapter = new SSETransportAdapter({ heartbeatInterval: 15000 });
 *
 * // In API route
 * const response = await sseAdapter.createConnection(connectionId, request);
 * return response; // Returns SSE stream
 *
 * // Send message
 * await sseAdapter.send(connectionId, {
 *   event: 'progress',
 *   data: { percentage: 50 },
 * });
 * ```
 */
export declare class SSETransportAdapter extends BaseTransportAdapter {
    private connections;
    constructor(config?: Partial<StreamTransportAdapterConfig>);
    /**
     * Create a new SSE connection
     *
     * @param connectionId - Unique connection identifier
     * @returns Response with SSE stream
     */
    createConnection(connectionId: string): Promise<Response>;
    /**
     * Send a message to a connection
     *
     * @param connectionId - Connection to send to
     * @param message - Message to send
     */
    send(connectionId: string, message: StreamMessage): Promise<void>;
    /**
     * Close a connection
     *
     * @param connectionId - Connection to close
     */
    close(connectionId: string): Promise<void>;
    /**
     * Check if a connection is alive
     *
     * @param connectionId - Connection to check
     */
    isAlive(connectionId: string): boolean;
    /**
     * Get current connection count
     */
    getConnectionCount(): number;
    /**
     * Get all connection IDs
     */
    getConnectionIds(): string[];
    /**
     * Send message immediately to controller
     */
    private sendImmediate;
    /**
     * Format message as SSE
     *
     * SSE format:
     * ```
     * id: messageId
     * retry: retryMs
     * data: {"event":"eventName","channel":"channelName","data":{...}}
     *
     * ```
     *
     * Note: We intentionally DON'T use SSE named events (event: line) because:
     * 1. EventSource silently drops events without registered listeners
     * 2. Hardcoding all possible event names is not scalable
     * 3. Including event in JSON payload is more flexible
     *
     * The client extracts event/channel from the JSON payload in onmessage.
     */
    private formatSSE;
    /**
     * Cleanup connection resources
     */
    private cleanup;
    /**
     * Close all connections (for shutdown)
     */
    closeAll(): Promise<void>;
}
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