import { KeyValueStorage } from "./KeyValueStorage";
export declare class FeatureStorage extends KeyValueStorage {
    static readonly FEATURE_PREFIX = "sinch:features:";
    static readonly LAST_REFRESHED_AT = "LastRefreshedAt";
    static readonly REFRESH_INTERVAL_MS: number;
    private static readonly STORAGE_KEYS;
    private userId?;
    private applicationKey?;
    constructor(storage: Storage);
    setApplicationConfig(userId: string, applicationKey: string): void;
    getFeatureFlag(featureFlag: string): boolean | number | undefined;
    setFeatureFlag(featureFlag: string, value: boolean | number): void;
    isEmpty(): boolean;
    removeAll(): void;
    get lastRefreshedAt(): number;
    set lastRefreshedAt(dateInMilliseconds: number);
    private isApplicationConfigSet;
    private getPrefixedFeatureFlagKey;
}