import { ConfigBody } from './config/configBody';
export declare const isValidDate: (date: Date | null) => date is Date;
/**
 * Interface representing a source to pull config data from. Used by the Node and Next SDKs
 */
export declare abstract class ConfigSource {
    configEtag?: string;
    configLastModified?: string;
    /**
     * Method to get the config from the source.
     * Should return null if the config has not changed, and throw an error if it could not be retrieved.
     * @param sdkKey
     * @param kind
     * @param obfuscated
     * @param lastModifiedThreshold
     * @param skipLastModified
     */
    abstract getConfig<T extends boolean = false>(sdkKey: string, kind: 'server' | 'bootstrap', obfuscated: boolean, lastModifiedThreshold?: string, skipLastModified?: T): Promise<{
        config: T extends true ? ConfigBody : ConfigBody | null;
        lastModified: string | null;
        metaData: Record<string, unknown>;
    }>;
    /**
     * Return the URL (or path or storage key etc.) that will be used to retrieve the config for the given SDK key
     * @param sdkKey
     * @param kind
     * @param obfuscated
     */
    abstract getConfigURL(sdkKey: string, kind: 'server' | 'bootstrap', obfuscated: boolean): string;
    protected isLastModifiedHeaderOld(lastModifiedHeader: string | null): boolean;
}