import { EventEmitter } from './event-emitter';
/**
 * Per-flag metrics summary.
 */
export interface FlagMetric {
    evaluations: number;
    cacheHits: number;
    cacheMisses: number;
    changes: number;
    lastEvaluatedAt: number;
    latencies: number[];
}
/**
 * Experiment exposure summary.
 */
export interface ExperimentMetric {
    experimentId: string;
    exposures: number;
    variationCounts: Record<string, number>;
}
/**
 * Full metrics snapshot returned by `getSnapshot()`.
 */
export interface MetricsSnapshot {
    totalEvaluations: number;
    totalCacheHits: number;
    totalCacheMisses: number;
    cacheHitRate: number;
    flags: Record<string, FlagMetric>;
    experiments: Record<string, ExperimentMetric>;
    latency: {
        p50: number;
        p95: number;
        p99: number;
        avg: number;
    };
    collectedSince: number;
}
/**
 * Passive impact metrics collector.
 *
 * Subscribes to SDK events and aggregates per-flag evaluation counts,
 * cache hit/miss ratios, latency percentiles, change frequency,
 * and experiment exposure counts. No network calls, no external dependencies.
 *
 * @example
 * ```ts
 * const metrics = client.getImpactMetrics();
 * console.log(metrics.cacheHitRate);         // 0.87
 * console.log(metrics.latency.p95);          // 12ms
 * console.log(metrics.flags['my-flag'].evaluations); // 42
 * ```
 */
export declare class ImpactMetrics {
    private totalEvaluations;
    private totalCacheHits;
    private totalCacheMisses;
    private readonly flags;
    private readonly experiments;
    private readonly latencies;
    private readonly collectedSince;
    private readonly unsubscribers;
    constructor(events: EventEmitter);
    /**
     * Returns a full immutable snapshot of all collected metrics.
     */
    getSnapshot(): MetricsSnapshot;
    /**
     * Reset all collected metrics.
     */
    reset(): void;
    /**
     * Unsubscribe from all events. Called on client dispose.
     */
    destroy(): void;
    private getOrCreateFlag;
    private getOrCreateExperiment;
    private computeLatencyPercentiles;
}