perf(bg/PaymentSession): fewer quote requests using exchange rate

src/background/services/paymentSession.ts

@@ -15,7 +15,13 @@ import {
   isOutOfBalanceError,
   isTokenExpiredError,
 } from '@/background/services/openPayments';
-import { bigIntMax, convert, getNextSendableAmount } from '@/background/utils';
+import {
+  bigIntMax,
+  convert,
+  convertWithExchangeRate,
+  getExchangeRatesMemoized,
+  getNextSendableAmount,
+} from '@/background/utils';
 import type {
   MonetizationEventDetails,
   MonetizationEventPayload,
@@ -144,6 +150,19 @@ export class PaymentSession {
       }
     }
 
+    if (isCrossCurrency) {
+      try {
+        const exchangeRates = await getExchangeRatesMemoized();
+        amountToSend = convertWithExchangeRate(
+          amountToSend,
+          this.receiver,
+          this.sender,
+          exchangeRates,
+        );
+        this.logger.debug('minSendAmount: via exchangeRate', amountToSend);
+      } catch {}
+    }
+
     // This all will eventually get replaced by OpenPayments response update
     // that includes a min rate that we can directly use.
     await this.setIncomingPaymentUrl();

src/background/utils.ts

@@ -10,7 +10,7 @@ import type { Browser, Runtime } from 'webextension-polyfill';
 import { BACKGROUND_TO_POPUP_CONNECTION_NAME } from '@/shared/messages';
 import { EXCHANGE_RATES_URL } from './config';
 import { INTERNAL_PAGE_URL_PROTOCOLS, NEW_TAB_PAGES } from './constants';
-import { notNullOrUndef } from '@/shared/helpers';
+import { memoize, notNullOrUndef } from '@/shared/helpers';
 import type { WalletAddress } from '@interledger/open-payments';
 
 type OnConnectCallback = Parameters<
@@ -90,6 +90,11 @@ export const getExchangeRates = async (): Promise<ExchangeRates> => {
   return rates;
 };
 
+export const getExchangeRatesMemoized = memoize(getExchangeRates, {
+  maxAge: 15 * 60 * 1000,
+  mechanism: 'stale-while-revalidate',
+});
+
 export const getExchangeRate = (
   rates: ExchangeRates,
   forAssetCode: string,
@@ -121,7 +126,7 @@ export const convertWithExchangeRate = <T extends AmountValue | bigint>(
   const scaleDiff = from.assetScale - to.assetScale;
   const scaledExchangeRate = exchangeRate * 10 ** scaleDiff;
 
-  const converted = BigInt(Math.ceil(Number(amount) / scaledExchangeRate));
+  const converted = BigInt(Math.round(Number(amount) / scaledExchangeRate));
 
   return typeof amount === 'string'
     ? (converted.toString() as T)

src/shared/helpers/misc.ts

@@ -55,6 +55,26 @@ export function withResolvers<T>() {
   return { resolve, reject, promise };
 }
 
+export function memoize<T extends () => Promise<unknown>>(
+  fn: T,
+  options: { maxAge: number; mechanism: 'stale-while-revalidate' | 'max-age' },
+): () => ReturnType<T> {
+  const { maxAge, mechanism = 'max-age' } = options;
+  let result: ReturnType<T>;
+  let lastCall = 0;
+  return () => {
+    const lastResult = result;
+    if (Date.now() - lastCall > maxAge) {
+      lastCall = Date.now();
+      result = fn() as ReturnType<T>;
+    }
+    if (mechanism === 'stale-while-revalidate') {
+      return lastResult;
+    }
+    return result;
+  };
+}
+
 export const isOkState = (state: Storage['state']) => {
   return Object.values(state).every((value) => value === false);
 };