/**
 * @class
 * @description Tracks per-CDN time-at-each-concurrency-level. Mirrors the
 * Android `StatsCollector` concurrency tracking:
 *
 *   - L0 = fraction of time with zero in-flight requests (CDN idle).
 *   - L1, L2, ... = fraction with 1, 2, ... concurrent requests.
 *   - `snapshotEmaRatio()` returns the EMA fractions (tau = 60_000ms).
 *   - `snapshotDeltaSinceLastTick()` returns the histogram of the last
 *     tick window AND folds it into the EMA (resets the per-tick accumulator).
 *
 * Typical caller pattern: every 5s do `delta = snapshotDeltaSinceLastTick()`
 * (which also updates the EMA), then `ema = snapshotEmaRatio()`.
 *
 * `getL0()` is the convenience used by the dynamic-trial-timeout (PR4).
 * @exports ConcurrencyEma
 */
export default class ConcurrencyEma {
    static readonly TAU_MS = 60000;
    private readonly nowFn;
    private currentLevel;
    private lastTransitionAt;
    private lastEmaUpdateAt;
    private startedAt;
    private deltaTimePerLevel;
    private emaRatio;
    constructor(now?: () => number);
    /** A new in-flight request started on this CDN. */
    recordStart(): void;
    /** An in-flight request on this CDN ended (success, fail or abort). */
    recordEnd(): void;
    /**
     * Snapshot the per-level fraction-of-time histogram for the last tick
     * window, fold it into the EMA, and reset the per-tick accumulator.
     * Returns the pre-reset fractions (sum to 1.0 when there is data).
     */
    snapshotDeltaSinceLastTick(): Map<number, number>;
    /** Return a copy of the current EMA fractions. */
    snapshotEmaRatio(): Map<number, number>;
    /** Convenience: current EMA fraction-of-time idle (0 in-flight). */
    getL0(): number;
    /** Total elapsed time since this collector was created. */
    getSessionMs(): number;
    /** Current in-flight count (mostly for debugging). */
    getCurrentLevel(): number;
    private accrueElapsed;
    private foldIntoEma;
    private static sumValues;
}