gas price estimator

1 files changed, 45 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..bd81ea05f
--- /dev/null
+++ b/packages/instant/src/util/gas_price_estimator.ts
@@ -0,0 +1,45 @@
+import { BigNumber } from '@0x/utils';
+
+// TODO: merge development and move to constants
+const ENDPOINT_URL = 'https://ethgasstation.info/json/ethgasAPI.json';
+const DEFAULT_GAS_PRICE_WEI = new BigNumber(20000000000);
+
+interface GasStationResult {
+    average: number;
+    fastestWait: number;
+    fastWait: number;
+    fast: number;
+    safeLowWait: number;
+    blockNum: number;
+    avgWait: number;
+    block_time: number;
+    speed: number;
+    fastest: number;
+    safeLow: number;
+}
+
+const fetchFastAmountInWei = async () => {
+    const res = await fetch(ENDPOINT_URL);
+    const gasInfo = (await res.json()) as GasStationResult;
+    const gasPriceInGwei = new BigNumber(gasInfo.fast / 10);
+    return gasPriceInGwei.mul(1000000000);
+};
+
+export class GasPriceEstimator {
+    private _lastFetched?: BigNumber;
+    public async getFastAmountInWeiAsync(): Promise<BigNumber> {
+        let fetchedAmount: BigNumber | undefined;
+        try {
+            fetchedAmount = await fetchFastAmountInWei();
+        } catch {
+            fetchedAmount = undefined;
+        }
+
+        if (fetchedAmount) {
+            this._lastFetched = fetchedAmount;
+        }
+
+        return fetchedAmount || this._lastFetched || DEFAULT_GAS_PRICE_WEI;
+    }
+}
+export const gasPriceEstimator = new GasPriceEstimator();