feat: add rate limiting for CoinGecko API and global error handling

js/services/currency.js

@@ -16,24 +16,59 @@ const CURRENCY_SYMBOLS = {
     JPY: '¥'
 }
 
-const CACHE_DURATION = 5 * 60 * 1000 // 5 minutes
+const CACHE_DURATION = 10 * 60 * 1000 // 10 minutes (CoinGecko free tier: 10-30 req/min)
+const MIN_REQUEST_INTERVAL = 6 * 1000 // 6 seconds between requests (max ~10/min)
 
 let cachedRates = null
 let cacheTimestamp = 0
+let lastRequestTime = 0
+let pendingRequest = null
 
 /**
- * Fetches current XMR rates from CoinGecko
+ * Fetches current XMR rates from CoinGecko with rate limiting
  * @returns {Promise<Object>} Rates per currency (e.g. { EUR: 329.05, USD: 388.87 })
  */
 export async function getXmrRates() {
-    // Check cache
+    // Return cached rates if still valid
     if (cachedRates && Date.now() - cacheTimestamp < CACHE_DURATION) {
         return cachedRates
     }
 
+    // If a request is already pending, wait for it
+    if (pendingRequest) {
+        return pendingRequest
+    }
+
+    // Rate limiting: ensure minimum interval between requests
+    const timeSinceLastRequest = Date.now() - lastRequestTime
+    if (timeSinceLastRequest < MIN_REQUEST_INTERVAL && cachedRates) {
+        return cachedRates
+    }
+
+    // Create and store the pending request
+    pendingRequest = fetchRates()
+    
+    try {
+        const rates = await pendingRequest
+        return rates
+    } finally {
+        pendingRequest = null
+    }
+}
+
+async function fetchRates() {
+    lastRequestTime = Date.now()
+    
     try {
         const currencies = 'eur,usd,gbp,chf,jpy'
         const response = await fetch(`${COINGECKO_API}?ids=monero&vs_currencies=${currencies}`)
+        
+        // Handle rate limit response
+        if (response.status === 429) {
+            console.warn('CoinGecko rate limit hit, using cached rates')
+            return cachedRates || getDefaultRates()
+        }
+        
         const data = await response.json()
 
         if (!data.monero) {