import { type Counter, type Histogram, metrics } from "@opentelemetry/api";

/**
 * OTel instruments for the Date formatter.
 *
 * Histogram records per-format wall-clock duration; the counter
 * increments on every cache reuse so consumers can observe cache
 * effectiveness.
 *
 * The module retains a small in-memory state ring so spec-conformance
 * tests can assert exact attribute payloads without standing up a
 * full SDK exporter.
 */

export interface DateMetricSample {
    readonly attributes: Record<string, string | number>;
}

export interface DateMetricsState {
    readonly durationSamples: DateMetricSample[];
    readonly cacheHitSamples: DateMetricSample[];
}

let cached:
    | {
          readonly durationMs: Histogram;
          readonly cacheHit: Counter;
      }
    | undefined;

const state: DateMetricsState = {
    durationSamples: [],
    cacheHitSamples: [],
};

function ensureInstruments() {
    if (cached) return cached;
    const meter = metrics.getMeter("suaveplan.i18n.formatter.date");
    cached = {
        durationMs: meter.createHistogram("i18n.format.date.duration_ms", {
            description:
                "Duration in ms of DateFormatter.format / formatDateRange; labels: locale, preset.",
            unit: "ms",
        }),
        cacheHit: meter.createCounter("i18n.format.cache_hit", {
            description:
                "Format-time cache reuse counter; labels: formatter (date).",
        }),
    };
    return cached;
}

export function recordDateFormat(
    locale: string,
    preset: string,
    durationMs: number
): void {
    const ins = ensureInstruments();
    const attributes = { locale, preset };
    ins.durationMs.record(durationMs, attributes);
    state.durationSamples.push({ attributes });
}

export function recordDateCacheHit(): void {
    const ins = ensureInstruments();
    const attributes = { formatter: "date" };
    ins.cacheHit.add(1, attributes);
    state.cacheHitSamples.push({ attributes });
}

export function getDateMetricsState(): DateMetricsState {
    return state;
}

export function resetDateMetricsState(): void {
    state.durationSamples.length = 0;
    state.cacheHitSamples.length = 0;
}