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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<GasInfo> => {
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<GasInfo> {
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();
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