1 files changed, 62 insertions, 0 deletions
diff --git a/packages/instant/src/util/gas_price_estimator.ts b/packages/instant/src/util/gas_price_estimator.ts
new file mode 100644
index 000000000..6b15809a3
--- /dev/null
+++ b/packages/instant/src/util/gas_price_estimator.ts
@@ -0,0 +1,62 @@
+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();