import type { ExchangeApi } from './BaseExchangeApi';
import type { BigNumber as BigNumberJs } from 'bignumber.js';
export declare type RateWithExpiration = {
    rate: BigNumberJs;
    expirationTime: number;
};
export declare class ExchangeApiCache implements ExchangeApi {
    private exchangeApi;
    private expirationTimeInMillisec;
    private cache;
    constructor(exchangeApi: ExchangeApi, expirationTimeInMillisec: number, cache?: Map<string, RateWithExpiration>);
    queryExchangeRate(sourceCurrency: string, targetCurrency: string): Promise<BigNumberJs>;
}
export declare const getKeyFromArgs: (sourceCurrency: string, targetCurrency: string) => string;