fix: address PR comments

2 files changed, 48 insertions, 3 deletions

diff --git a/packages/instant/src/util/coinbase_api.ts b/packages/instant/src/util/coinbase_api.ts
index 080421f98..faac8d82d 100644
--- a/packages/instant/src/util/coinbase_api.ts
+++ b/packages/instant/src/util/coinbase_api.ts
@@ -1,9 +1,10 @@
-import { BigNumber } from '@0x/utils';
+import { BigNumber, fetchAsync } from '@0x/utils';
+
+import { COINBASE_API_BASE_URL } from '../constants';
 
-const baseEndpoint = 'https://api.coinbase.com/v2';
 export const coinbaseApi = {
     getEthUsdPrice: async (): Promise<BigNumber> => {
-        const res = await fetch(`${baseEndpoint}/prices/ETH-USD/buy`);
+        const res = await fetchAsync(`${COINBASE_API_BASE_URL}/prices/ETH-USD/buy`);
         const resJson = await res.json();
         return new BigNumber(resJson.data.amount);
     },
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..336c4a3fa
--- /dev/null
+++ b/packages/instant/src/util/gas_price_estimator.ts
@@ -0,0 +1,44 @@
+import { BigNumber, fetchAsync } from '@0x/utils';
+
+import { 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;
+}
+
+const fetchFastAmountInWeiAsync = async () => {
+    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);
+    return gasPriceInGwei.mul(GWEI_IN_WEI);
+};
+
+export class GasPriceEstimator {
+    private _lastFetched?: BigNumber;
+    public async getFastAmountInWeiAsync(): Promise<BigNumber> {
+        let fetchedAmount: BigNumber | undefined;
+        try {
+            fetchedAmount = await fetchFastAmountInWeiAsync();
+        } catch {
+            fetchedAmount = undefined;
+        }
+
+        if (fetchedAmount) {
+            this._lastFetched = fetchedAmount;
+        }
+
+        return fetchedAmount || this._lastFetched || DEFAULT_GAS_PRICE;
+    }
+}
+export const gasPriceEstimator = new GasPriceEstimator();