import type { PipelineTraceStep } from '../pipeline/types.js';
/** Where metrics go: counters, histograms, and gauges, labelled. */
export interface MetricsSink {
    /** Adds to a counter. */
    increment(name: string, value?: number, labels?: Record<string, string>): void | Promise<void>;
    /** Records a value in a histogram, such as a latency. */
    observe(name: string, value: number, labels?: Record<string, string>): void | Promise<void>;
    /** Sets a gauge. */
    gauge?(name: string, value: number, labels?: Record<string, string>): void | Promise<void>;
}
/** Metrics collection for a client. */
export interface MetricsConfig {
    /** Turns collection on. Off by default, and then nothing is recorded. */
    enabled?: boolean;
    /**
     * Where metrics go. Defaults to an in-memory sink, readable through `getMetricsSnapshot()` and
     * `getPrometheusMetrics()`.
     */
    sink?: MetricsSink;
    /** Prefix for metric names. Defaults to `nexus_ai`. */
    prefix?: string;
    /**
     * Ignored: Prometheus text is always available from `getPrometheusMetrics()`.
     *
     * @deprecated Has never been read. It will be removed in 2.0.
     */
    prometheus?: boolean;
}
/** Keeps metrics in memory, for a snapshot or a Prometheus scrape. */
export declare class InMemoryMetrics implements MetricsSink {
    private counters;
    private histograms;
    private gauges;
    /** Adds to a counter. */
    increment(name: string, value?: number, labels?: Record<string, string>): void;
    /** Records a value in a histogram. */
    observe(name: string, value: number, labels?: Record<string, string>): void;
    /** Sets a gauge. */
    gauge(name: string, value: number, labels?: Record<string, string>): void;
    /** Every metric as plain data: counters, histogram count, average and maximum, and gauges. */
    snapshot(): Record<string, unknown>;
    /** Every metric in Prometheus text exposition format. */
    toPrometheus(prefix?: string): string;
    private key;
}
/** The part of an OpenTelemetry meter the metrics sink uses. */
export interface OpenTelemetryLikeMeter {
    /** Creates a counter. */
    createCounter(name: string): {
        add(value: number, labels?: Record<string, string>): void;
    };
    /** Creates a histogram. */
    createHistogram(name: string): {
        record(value: number, labels?: Record<string, string>): void;
    };
    /** Creates an observable gauge. */
    createObservableGauge?: (name: string) => unknown;
}
/** Sends metrics to OpenTelemetry through a meter. */
export declare class OpenTelemetryMetricsSink implements MetricsSink {
    private meter;
    private counters;
    private histograms;
    constructor(meter: OpenTelemetryLikeMeter);
    /** Adds to a counter, creating it on first use. */
    increment(name: string, value?: number, labels?: Record<string, string>): void;
    /** Records a value in a histogram, creating it on first use. */
    observe(name: string, value: number, labels?: Record<string, string>): void;
}
/**
 * Records request, response, error, and pipeline-step metrics for a client, when metrics are
 * enabled.
 */
export declare class MetricsCollector {
    private config;
    private memory;
    private sink?;
    private prefix;
    constructor(config?: MetricsConfig);
    /** Counts a request. */
    recordRequest(labels: Record<string, string>): Promise<void>;
    /** Counts an error. */
    recordError(labels: Record<string, string>): Promise<void>;
    /** Counts a response and records its latency and cost. */
    recordResponse(labels: Record<string, string>, latencyMs: number, cost?: number): Promise<void>;
    /** Records how long a pipeline stage took. */
    recordStep(step: PipelineTraceStep): Promise<void>;
    /** The in-memory metrics, as plain data. */
    snapshot(): Record<string, unknown>;
    /** The in-memory metrics, in Prometheus text format. */
    toPrometheus(): string;
}