/**
 * Metrics Collection System
 *
 * Collect and expose application metrics for monitoring
 */
export type MetricType = 'counter' | 'gauge' | 'histogram' | 'summary';
export interface MetricLabels {
    [key: string]: string | number;
}
export interface MetricValue {
    value: number;
    timestamp: number;
    labels?: MetricLabels;
}
export interface Metric {
    name: string;
    type: MetricType;
    help: string;
    values: MetricValue[];
    labels?: string[];
}
export interface HistogramBucket {
    le: number;
    count: number;
}
export interface HistogramMetric extends Metric {
    type: 'histogram';
    buckets: HistogramBucket[];
    sum: number;
    count: number;
}
export declare class MetricsCollector {
    private metrics;
    /**
     * Register a counter metric
     */
    counter(name: string, help: string, labels?: string[]): Counter;
    /**
     * Register a gauge metric
     */
    gauge(name: string, help: string, labels?: string[]): Gauge;
    /**
     * Register a histogram metric
     */
    histogram(name: string, help: string, buckets?: number[], labels?: string[]): Histogram;
    /**
     * Get all metrics
     */
    getMetrics(): Metric[];
    /**
     * Get metric by name
     */
    getMetric(name: string): Metric | undefined;
    /**
     * Clear all metrics
     */
    clear(): void;
    /**
     * Export metrics in Prometheus format
     */
    exportPrometheus(): string;
    /**
     * Export metrics as JSON
     */
    exportJSON(): Record<string, unknown>;
}
/**
 * Counter metric
 */
export declare class Counter {
    private metric;
    constructor(metric: Metric);
    /**
     * Increment counter
     */
    inc(value?: number, labels?: MetricLabels): void;
    /**
     * Get current value
     */
    get(labels?: MetricLabels): number;
    /**
     * Find value by labels
     */
    private findValue;
    /**
     * Check if labels match
     */
    private labelsMatch;
}
/**
 * Gauge metric
 */
export declare class Gauge {
    private metric;
    constructor(metric: Metric);
    /**
     * Set gauge value
     */
    set(value: number, labels?: MetricLabels): void;
    /**
     * Increment gauge
     */
    inc(value?: number, labels?: MetricLabels): void;
    /**
     * Decrement gauge
     */
    dec(value?: number, labels?: MetricLabels): void;
    /**
     * Get current value
     */
    get(labels?: MetricLabels): number;
    /**
     * Find value by labels
     */
    private findValue;
    /**
     * Check if labels match
     */
    private labelsMatch;
}
/**
 * Histogram metric
 */
export declare class Histogram {
    private metric;
    constructor(metric: HistogramMetric);
    /**
     * Observe a value
     */
    observe(value: number, labels?: MetricLabels): void;
    /**
     * Start a timer
     */
    startTimer(labels?: MetricLabels): () => void;
    /**
     * Get percentile
     */
    percentile(p: number): number;
    /**
     * Get average
     */
    average(): number;
}
/**
 * Default metrics collector
 */
export declare const metrics: MetricsCollector;
/**
 * Application metrics
 */
export declare const appMetrics: {
    httpRequestsTotal: Counter;
    httpRequestDuration: Histogram;
    dbQueriesTotal: Counter;
    dbQueryDuration: Histogram;
    cacheOperationsTotal: Counter;
    cacheHitRate: Gauge;
    activeConnections: Gauge;
    errorsTotal: Counter;
    queueSize: Gauge;
    queueProcessingDuration: Histogram;
    memoryUsage: Gauge;
    apiCallsTotal: Counter;
    apiCallDuration: Histogram;
    x402PaymentRequiredTotal: Counter;
    x402PaymentVerifyTotal: Counter;
    x402PaymentVerifyDuration: Histogram;
};
/**
 * Track HTTP request
 */
export declare function trackHTTPRequest(method: string, path: string, status: number, duration: number): void;
/**
 * Track database query
 */
export declare function trackDBQuery(operation: string, table: string, duration: number): void;
/**
 * Track cache operation
 */
export declare function trackCacheOperation(operation: 'hit' | 'miss' | 'set' | 'delete', result?: 'success' | 'error'): void;
/**
 * Track error
 */
export declare function trackError(type: string, severity?: 'low' | 'medium' | 'high' | 'critical'): void;
/**
 * Update active connections
 */
export declare function updateActiveConnections(type: string, delta: number): void;
/**
 * Track an x402 HTTP 402 emission at a route. Call when the route returns
 * 402 with `X-PAYMENT-REQUIRED`. `currency` is always `'usdc-only'` — USDC on
 * Base is the sole settlement currency.
 */
export declare function trackX402PaymentRequired(route: string, currency: 'usdc-only'): void;
/**
 * Track an x402 payment verification. Increments the result counter and
 * observes the duration histogram (latency = Coinbase facilitator round-trip
 * for USDC).
 */
export declare function trackX402PaymentVerify(route: string, scheme: 'exact', result: 'valid' | 'invalid', durationMs: number): void;
/**
 * Update memory usage
 */
export declare function updateMemoryUsage(): void;
/**
 * Start memory monitoring
 */
export declare function startMemoryMonitoring(intervalMs?: number): NodeJS.Timeout;
/**
 * Create metrics middleware
 */
export declare function createMetricsMiddleware<TRequest = unknown, TResponse = unknown>(): (request: TRequest & {
    method: string;
    url: string;
}, next: () => Promise<TResponse & {
    status?: number;
}>) => Promise<TResponse & {
    status?: number;
}>;
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