From 8ab8c279989114662d6dce4b5b998ad8fd88fc1a Mon Sep 17 00:00:00 2001
From: Steve Klebanoff <steve.klebanoff@gmail.com>
Date: Mon, 29 Oct 2018 15:19:48 -0700
Subject: gas price estimator

---
 packages/instant/src/components/buy_button.tsx     |  5 ++-
 .../instant/src/components/zero_ex_instant.tsx     |  2 +
 packages/instant/src/util/gas_price_estimator.ts   | 45 ++++++++++++++++++++++
 3 files changed, 50 insertions(+), 2 deletions(-)
 create mode 100644 packages/instant/src/util/gas_price_estimator.ts

(limited to 'packages/instant/src')

diff --git a/packages/instant/src/components/buy_button.tsx b/packages/instant/src/components/buy_button.tsx
index e65e62e47..58575b1b3 100644
--- a/packages/instant/src/components/buy_button.tsx
+++ b/packages/instant/src/components/buy_button.tsx
@@ -7,6 +7,7 @@ import { ColorOption } from '../style/theme';
 import { ZeroExInstantError } from '../types';
 import { getBestAddress } from '../util/address';
 import { balanceUtil } from '../util/balance';
+import { gasPriceEstimator } from '../util/gas_price_estimator';
 import { util } from '../util/util';
 import { web3Wrapper } from '../util/web3_wrapper';
 
@@ -56,9 +57,9 @@ export class BuyButton extends React.Component<BuyButtonProps> {
         }
 
         let txHash: string | undefined;
+        const gasPrice = await gasPriceEstimator.getFastAmountInWeiAsync();
         try {
-            const gasPrice = DEFAULT_GAS_PRICE;
-            txHash = await assetBuyer.executeBuyQuoteAsync(buyQuote, { gasPrice, takerAddress });
+            txHash = await assetBuyer.executeBuyQuoteAsync(buyQuote, { takerAddress, gasPrice });
         } catch (e) {
             if (e instanceof Error) {
                 if (e.message === AssetBuyerError.SignatureRequestDenied) {
diff --git a/packages/instant/src/components/zero_ex_instant.tsx b/packages/instant/src/components/zero_ex_instant.tsx
index 19a2d6b9b..6a5846963 100644
--- a/packages/instant/src/components/zero_ex_instant.tsx
+++ b/packages/instant/src/components/zero_ex_instant.tsx
@@ -13,6 +13,7 @@ import { AssetMetaData, Network } from '../types';
 import { assetUtils } from '../util/asset';
 import { BigNumberInput } from '../util/big_number_input';
 import { errorFlasher } from '../util/error_flasher';
+import { gasPriceEstimator } from '../util/gas_price_estimator';
 import { getProvider } from '../util/provider';
 import { web3Wrapper } from '../util/web3_wrapper';
 
@@ -78,6 +79,7 @@ export class ZeroExInstant extends React.Component<ZeroExInstantProps> {
     public componentDidMount(): void {
         // tslint:disable-next-line:no-floating-promises
         asyncData.fetchAndDispatchToStore(this._store);
+        gasPriceEstimator.getFastAmountInWeiAsync();
         // tslint:disable-next-line:no-floating-promises
         this._flashErrorIfWrongNetwork();
     }
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();
-- 
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