import { BigNumber, fetchAsync } from '@0x/utils'; import { DEFAULT_ESTIMATED_TRANSACTION_TIME_MS, DEFAULT_GAS_PRICE, ETH_GAS_STATION_API_BASE_URL, GWEI_IN_WEI, } from '../constants'; interface EthGasStationResult { average: number; fastestWait: number; fastWait: number; fast: number; safeLowWait: number; blockNum: number; avgWait: number; block_time: number; speed: number; fastest: number; safeLow: number; } interface GasInfo { gasPriceInWei: BigNumber; estimatedTimeMs: number; } const fetchFastAmountInWeiAsync = async (): Promise => { const res = await fetchAsync(`${ETH_GAS_STATION_API_BASE_URL}/json/ethgasAPI.json`); const gasInfo = (await res.json()) as EthGasStationResult; // Eth Gas Station result is gwei * 10 const gasPriceInGwei = new BigNumber(gasInfo.fast / 10); // Time is in minutes const estimatedTimeMs = gasInfo.fastWait * 60 * 1000; // Minutes to MS return { gasPriceInWei: gasPriceInGwei.mul(GWEI_IN_WEI), estimatedTimeMs }; }; export class GasPriceEstimator { private _lastFetched?: GasInfo; public async getGasInfoAsync(): Promise { let fetchedAmount: GasInfo | undefined; try { fetchedAmount = await fetchFastAmountInWeiAsync(); } catch { fetchedAmount = undefined; } if (fetchedAmount) { this._lastFetched = fetchedAmount; } return ( fetchedAmount || this._lastFetched || { gasPriceInWei: DEFAULT_GAS_PRICE, estimatedTimeMs: DEFAULT_ESTIMATED_TRANSACTION_TIME_MS, } ); } } export const gasPriceEstimator = new GasPriceEstimator();