feat: add currency setting with fiat conversion, display prices in user's preferred currency

js/services/currency.js

@@ -165,14 +165,44 @@ export function convertFromXmr(xmrAmount, currency, rates) {
     return xmrAmount * rates[currency]
 }
 
+/**
+ * Converts between fiat currencies using XMR as bridge
+ * @param {number} amount - Amount in source currency
+ * @param {string} fromCurrency - Source currency
+ * @param {string} toCurrency - Target currency
+ * @param {Object} rates - Rates from getXmrRates() (XMR -> Fiat)
+ * @returns {number} Amount in target currency
+ */
+export function convertFiat(amount, fromCurrency, toCurrency, rates) {
+    if (fromCurrency === toCurrency) return amount
+    if (!rates[fromCurrency] || !rates[toCurrency]) return amount
+    
+    // Use XMR as bridge: EUR -> XMR -> USD
+    // 1 XMR = rates[EUR] EUR, so 1 EUR = 1/rates[EUR] XMR
+    // 1 XMR = rates[USD] USD
+    // Therefore: 1 EUR = rates[USD] / rates[EUR] USD
+    return amount * (rates[toCurrency] / rates[fromCurrency])
+}
+
+/**
+ * Get user's preferred display currency from settings
+ * @returns {string} Currency code (default: 'USD')
+ */
+export function getDisplayCurrency() {
+    return localStorage.getItem('dgray_currency') || 'USD'
+}
+
 /**
  * Formats a price for display
+ * Shows price in user's preferred currency with XMR equivalent
  * @param {Object} listing - Listing with price, currency, price_mode
  * @param {Object} rates - Rates from getXmrRates()
+ * @param {string} [displayCurrency] - Override display currency
  * @returns {Object} { primary, secondary, xmrAmount }
  */
-export function formatPrice(listing, rates) {
+export function formatPrice(listing, rates, displayCurrency = null) {
     const { price, currency, price_mode } = listing
+    const userCurrency = displayCurrency || getDisplayCurrency()
 
     if (!price || price === 0) {
         return {
@@ -185,20 +215,25 @@ export function formatPrice(listing, rates) {
     // XMR mode: XMR is the reference price
     if (price_mode === 'xmr' || currency === 'XMR') {
         const xmrPrice = currency === 'XMR' ? price : convertToXmr(price, currency, rates)
-        const fiatEquivalent = currency !== 'XMR' ? price : convertFromXmr(price, 'EUR', rates)
+        const fiatEquivalent = convertFromXmr(xmrPrice, userCurrency, rates)
 
         return {
-            primary: formatXmr(xmrPrice),
-            secondary: currency !== 'XMR' ? `≈ ${formatFiat(price, currency)}` : `≈ ${formatFiat(fiatEquivalent, 'EUR')}`,
+            primary: formatFiat(fiatEquivalent, userCurrency),
+            secondary: `≈ ${formatXmr(xmrPrice)}`,
             xmrAmount: xmrPrice
         }
     }
 
-    // Fiat mode: Fiat is the reference price
+    // Fiat mode: Convert to user's preferred currency
     const xmrEquivalent = convertToXmr(price, currency, rates)
+    
+    // Always show in user's currency as primary
+    const displayPrice = userCurrency === currency 
+        ? price 
+        : convertFiat(price, currency, userCurrency, rates)
 
     return {
-        primary: formatFiat(price, currency),
+        primary: formatFiat(displayPrice, userCurrency),
         secondary: `≈ ${formatXmr(xmrEquivalent)}`,
         xmrAmount: xmrEquivalent
     }
@@ -253,8 +288,10 @@ export const SUPPORTED_CURRENCIES = ['XMR', 'EUR', 'CHF', 'USD', 'GBP', 'JPY']
 
 export default {
     getXmrRates,
+    getDisplayCurrency,
     convertToXmr,
     convertFromXmr,
+    convertFiat,
     formatPrice,
     formatXmr,
     formatFiat,