/**
 * Heartbeat Service
 *
 * Writes a TTL key to Redis at a regular interval to signal pod liveness.
 * When a pod dies, its heartbeat key expires and other pods can detect the death.
 */
import { type HaConfig, type HeartbeatValue } from './ha.types';
/**
 * Minimal Redis client interface (subset of ioredis).
 * Allows the service to work with any Redis-compatible client.
 */
export interface HeartbeatRedisClient {
    set(key: string, value: string, expiryMode: 'PX', time: number): Promise<unknown>;
    get(key: string): Promise<string | null>;
    del(key: string): Promise<number>;
    exists(key: string): Promise<number>;
    keys(pattern: string): Promise<string[]>;
}
export declare class HeartbeatService {
    private readonly redis;
    private readonly nodeId;
    private timer;
    private readonly startedAt;
    private readonly keyPrefix;
    private readonly intervalMs;
    private readonly ttlMs;
    private sessionCount;
    constructor(redis: HeartbeatRedisClient, nodeId: string, config?: Partial<HaConfig>);
    /** Start the heartbeat interval. */
    start(): void;
    /** Stop the heartbeat and remove the key. */
    stop(): Promise<void>;
    /** Update the tracked session count (for monitoring). */
    setSessionCount(count: number): void;
    /** Check if a specific node's heartbeat is alive. */
    isAlive(nodeId: string): Promise<boolean>;
    /** Get the heartbeat value for a specific node. */
    getHeartbeat(nodeId: string): Promise<HeartbeatValue | null>;
    /** Get all alive node IDs by scanning heartbeat keys. */
    getAliveNodes(): Promise<string[]>;
    private heartbeatKey;
    private writeHeartbeat;
}
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