fixup! Reorganize & clean exchange-rate logic

Author: swansontec

src/actions/ExchangeRateActions.ts

@@ -35,7 +35,7 @@ type AssetPair = ReturnType<typeof asAssetPair>
 type ExchangeRateCache = ReturnType<typeof asExchangeRateCache>
 type ExchangeRateCacheFile = ReturnType<typeof asExchangeRateCacheFile>
 
-const exchangeRateCache: ExchangeRateCache = {}
+let exchangeRateCache: ExchangeRateCache = {}
 
 const asRatesResponse = asObject({
   data: asArray(
@@ -74,8 +74,18 @@ async function buildExchangeRates(state: RootState): Promise<GuiExchangeRates> {
   let hasWallets = false
   let hasCachedRates = false
 
-  // Load exchange rate cache off disk, if we haven't done that yet:
-  if (Object.keys(exchangeRateCache).length === 0) {
+  // If we have loaded the cache before, keep any un-expired entries:
+  const rateCache: ExchangeRateCache = {}
+  const cachedKeys = Object.keys(exchangeRateCache)
+  if (cachedKeys.length > 0) {
+    for (const key of cachedKeys) {
+      if (exchangeRateCache[key].expiration > now) {
+        rateCache[key] = exchangeRateCache[key]
+        hasCachedRates = true
+      }
+    }
+  } else {
+    // Load exchange rate cache off disk, since we haven't done that yet:
     try {
       const raw = await disklet.getText(EXCHANGE_RATES_FILENAME)
       const json = JSON.parse(raw)
@@ -84,7 +94,7 @@ async function buildExchangeRates(state: RootState): Promise<GuiExchangeRates> {
       // Keep un-expired rates:
       for (const key of Object.keys(rates)) {
         if (rates[key].expiration > now) {
-          exchangeRateCache[key] = rates[key]
+          rateCache[key] = rates[key]
           hasCachedRates = true
         }
       }
@@ -185,13 +195,13 @@ async function buildExchangeRates(state: RootState): Promise<GuiExchangeRates> {
             const key = isHistorical ? `${currencyPair}_${date}` : currencyPair
 
             if (exchangeRate != null) {
-              exchangeRateCache[key] = {
+              rateCache[key] = {
                 expiration: rateExpiration,
                 rate: exchangeRate
               }
-            } else if (exchangeRateCache[key] == null) {
+            } else if (rateCache[key] == null) {
               // We at least need a placeholder:
-              exchangeRateCache[key] = {
+              rateCache[key] = {
                 expiration: 0,
                 rate: '0'
               }
@@ -208,18 +218,19 @@ async function buildExchangeRates(state: RootState): Promise<GuiExchangeRates> {
   // Save exchange rate cache to disk:
   try {
     const exchangeRateCacheFile: ExchangeRateCacheFile = {
-      rates: exchangeRateCache,
+      rates: rateCache,
       assetPairs: filteredAssetPairs
     }
     await disklet.setText(EXCHANGE_RATES_FILENAME, JSON.stringify(exchangeRateCacheFile))
   } catch (e) {
     datelog('Error saving exchange rate cache:', String(e))
   }
+  exchangeRateCache = rateCache
 
   // Build the GUI rate structure:
   const serverRates: GuiExchangeRates = { 'iso:USD_iso:USD': '1' }
-  for (const key of Object.keys(exchangeRateCache)) {
-    const { rate } = exchangeRateCache[key]
+  for (const key of Object.keys(rateCache)) {
+    const { rate } = rateCache[key]
     serverRates[key] = rate
 
     // Include reverse rates: