Add dual currency token display

frontend/src/components/common/DisplayCurrencyContext.tsx

@@ -0,0 +1,49 @@
+'use client'
+
+import { createContext, type ReactNode, useContext, useEffect, useMemo, useState } from 'react'
+
+export type DisplayCurrency = 'native' | 'usd'
+
+const DISPLAY_CURRENCY_STORAGE_KEY = 'explorer_display_currency'
+
+const DisplayCurrencyContext = createContext<{
+  currency: DisplayCurrency
+  setCurrency: (currency: DisplayCurrency) => void
+} | null>(null)
+
+export function DisplayCurrencyProvider({ children }: { children: ReactNode }) {
+  const [currency, setCurrencyState] = useState<DisplayCurrency>('native')
+
+  useEffect(() => {
+    if (typeof window === 'undefined') return
+    const stored = window.localStorage.getItem(DISPLAY_CURRENCY_STORAGE_KEY)
+    if (stored === 'native' || stored === 'usd') {
+      setCurrencyState(stored)
+    }
+  }, [])
+
+  const setCurrency = (nextCurrency: DisplayCurrency) => {
+    setCurrencyState(nextCurrency)
+    if (typeof window !== 'undefined') {
+      window.localStorage.setItem(DISPLAY_CURRENCY_STORAGE_KEY, nextCurrency)
+    }
+  }
+
+  const value = useMemo(
+    () => ({
+      currency,
+      setCurrency,
+    }),
+    [currency],
+  )
+
+  return <DisplayCurrencyContext.Provider value={value}>{children}</DisplayCurrencyContext.Provider>
+}
+
+export function useDisplayCurrency() {
+  const context = useContext(DisplayCurrencyContext)
+  if (!context) {
+    throw new Error('useDisplayCurrency must be used within a DisplayCurrencyProvider')
+  }
+  return context
+}

frontend/src/components/common/ExplorerChrome.tsx

@@ -2,25 +2,28 @@ import type { ReactNode } from 'react'
 import Navbar from './Navbar'
 import Footer from './Footer'
 import ExplorerAgentTool from './ExplorerAgentTool'
+import { DisplayCurrencyProvider } from './DisplayCurrencyContext'
 import { UiModeProvider } from './UiModeContext'
 
 export default function ExplorerChrome({ children }: { children: ReactNode }) {
   return (
     <UiModeProvider>
-      <div className="flex min-h-screen flex-col bg-gray-50 text-gray-900 dark:bg-gray-900 dark:text-gray-100">
-        <a
-          href="#main-content"
-          className="sr-only focus:not-sr-only focus:absolute focus:left-4 focus:top-4 focus:z-[100] focus:rounded-md focus:bg-primary-600 focus:px-4 focus:py-2 focus:text-sm focus:font-medium focus:text-white"
-        >
-          Skip to content
-        </a>
-        <Navbar />
-        <div id="main-content" className="flex-1">
-          {children}
+      <DisplayCurrencyProvider>
+        <div className="flex min-h-screen flex-col bg-gray-50 text-gray-900 dark:bg-gray-900 dark:text-gray-100">
+          <a
+            href="#main-content"
+            className="sr-only focus:not-sr-only focus:absolute focus:left-4 focus:top-4 focus:z-[100] focus:rounded-md focus:bg-primary-600 focus:px-4 focus:py-2 focus:text-sm focus:font-medium focus:text-white"
+          >
+            Skip to content
+          </a>
+          <Navbar />
+          <div id="main-content" className="flex-1">
+            {children}
+          </div>
+          <ExplorerAgentTool />
+          <Footer />
         </div>
-        <ExplorerAgentTool />
-        <Footer />
-      </div>
+      </DisplayCurrencyProvider>
     </UiModeProvider>
   )
 }

frontend/src/pages/tokens/[address].tsx

@@ -12,8 +12,10 @@ import { DetailRow } from '@/components/common/DetailRow'
 import EntityBadge from '@/components/common/EntityBadge'
 import GruStandardsCard from '@/components/common/GruStandardsCard'
 import { formatTokenAmount, formatTimestamp } from '@/utils/format'
+import { useDisplayCurrency } from '@/components/common/DisplayCurrencyContext'
 import { getGruStandardsProfileSafe, type GruStandardsProfile } from '@/services/api/gru'
 import { getGruExplorerMetadata } from '@/services/api/gruExplorerData'
+import { formatUsdValue, getSecondaryDisplayValue } from '@/utils/displayCurrency'
 
 function isValidAddress(value: string) {
   return /^0x[a-fA-F0-9]{40}$/.test(value)
@@ -31,15 +33,12 @@ function toNumeric(value: string | number | null | undefined): number | null {
 function formatUsd(value: string | number | null | undefined): string {
   const numeric = toNumeric(value)
   if (numeric == null) return 'Unavailable'
-  return new Intl.NumberFormat('en-US', {
-    style: 'currency',
-    currency: 'USD',
-    maximumFractionDigits: numeric >= 100 ? 0 : 2,
-  }).format(numeric)
+  return formatUsdValue(numeric)
 }
 
 export default function TokenDetailPage() {
   const router = useRouter()
+  const { currency, setCurrency } = useDisplayCurrency()
   const address = typeof router.query.address === 'string' ? router.query.address : ''
   const isValidTokenAddress = address !== '' && isValidAddress(address)
 
@@ -177,6 +176,28 @@ export default function TokenDetailPage() {
     [address, token?.address, token?.symbol],
   )
 
+  const renderAmountWithDisplayCurrency = useCallback(
+    (rawAmount: string | number | null | undefined, decimals: number, symbol?: string | null) => {
+      const primaryAmount = formatTokenAmount(rawAmount, decimals, symbol)
+      const secondaryAmount = getSecondaryDisplayValue({
+        rawAmount,
+        decimals,
+        exchangeRate: token?.exchange_rate,
+        displayCurrency: currency,
+      })
+
+      if (!secondaryAmount) return primaryAmount
+
+      return (
+        <div className="space-y-1">
+          <div>{primaryAmount}</div>
+          <div className="text-xs text-gray-500 dark:text-gray-400">Approx. {secondaryAmount}</div>
+        </div>
+      )
+    },
+    [currency, token?.exchange_rate],
+  )
+
   const holderColumns = [
     {
       header: 'Holder',
@@ -188,7 +209,7 @@ export default function TokenDetailPage() {
     },
     {
       header: 'Balance',
-      accessor: (holder: TokenHolder) => formatTokenAmount(holder.value, token?.decimals || holder.token_decimals, token?.symbol),
+      accessor: (holder: TokenHolder) => renderAmountWithDisplayCurrency(holder.value, token?.decimals || holder.token_decimals, token?.symbol),
     },
   ]
 
@@ -238,7 +259,7 @@ export default function TokenDetailPage() {
     },
     {
       header: 'Amount',
-      accessor: (transfer: AddressTokenTransfer) => formatTokenAmount(transfer.value, transfer.token_decimals, transfer.token_symbol),
+      accessor: (transfer: AddressTokenTransfer) => renderAmountWithDisplayCurrency(transfer.value, transfer.token_decimals, transfer.token_symbol),
     },
     {
       header: 'When',
@@ -316,9 +337,27 @@ export default function TokenDetailPage() {
               </DetailRow>
               <DetailRow label="Type">{token.type || 'Unknown'}</DetailRow>
               <DetailRow label="Decimals">{token.decimals}</DetailRow>
+              <DetailRow label="Display Currency">
+                <div className="space-y-2">
+                  <label className="inline-flex items-center gap-2 text-sm text-gray-700 dark:text-gray-300">
+                    <span className="sr-only">Display currency</span>
+                    <select
+                      value={currency}
+                      onChange={(event) => setCurrency(event.target.value === 'usd' ? 'usd' : 'native')}
+                      className="rounded-xl border border-gray-300 bg-white px-3 py-2 text-sm text-gray-900 shadow-sm focus:border-primary-500 focus:outline-none focus:ring-2 focus:ring-primary-200 dark:border-gray-600 dark:bg-gray-800 dark:text-gray-100 dark:focus:ring-primary-900"
+                    >
+                      <option value="native">Native token amounts</option>
+                      <option value="usd">USD estimate</option>
+                    </select>
+                  </label>
+                  <div className="text-xs text-gray-500 dark:text-gray-400">
+                    USD estimates use the explorer&apos;s current indicative token price and appear as a secondary line when available.
+                  </div>
+                </div>
+              </DetailRow>
               {token.total_supply && (
                 <DetailRow label="Total Supply">
-                  {formatTokenAmount(token.total_supply, token.decimals, token.symbol)}
+                  {renderAmountWithDisplayCurrency(token.total_supply, token.decimals, token.symbol)}
                 </DetailRow>
               )}
               {token.holders != null && (

frontend/src/utils/displayCurrency.test.ts

@@ -0,0 +1,47 @@
+import { describe, expect, it } from 'vitest'
+import { formatUsdValue, getSecondaryDisplayValue } from './displayCurrency'
+
+describe('formatUsdValue', () => {
+  it('keeps cents for smaller values', () => {
+    expect(formatUsdValue(4.5)).toBe('$4.50')
+  })
+
+  it('drops cents for larger rounded values', () => {
+    expect(formatUsdValue(1250)).toBe('$1,250')
+  })
+})
+
+describe('getSecondaryDisplayValue', () => {
+  it('returns null when the user prefers native display', () => {
+    expect(
+      getSecondaryDisplayValue({
+        rawAmount: '4500000',
+        decimals: 6,
+        exchangeRate: 1,
+        displayCurrency: 'native',
+      }),
+    ).toBeNull()
+  })
+
+  it('formats a USD secondary value from token units and exchange rate', () => {
+    expect(
+      getSecondaryDisplayValue({
+        rawAmount: '4500000',
+        decimals: 6,
+        exchangeRate: 1,
+        displayCurrency: 'usd',
+      }),
+    ).toBe('$4.50')
+  })
+
+  it('returns null when no usable exchange rate is available', () => {
+    expect(
+      getSecondaryDisplayValue({
+        rawAmount: '4500000',
+        decimals: 6,
+        exchangeRate: null,
+        displayCurrency: 'usd',
+      }),
+    ).toBeNull()
+  })
+})

frontend/src/utils/displayCurrency.ts

@@ -0,0 +1,35 @@
+import { formatUnits } from './format'
+
+function toFiniteNumber(value: string | number | null | undefined): number | null {
+  if (typeof value === 'number' && Number.isFinite(value)) return value
+  if (typeof value === 'string' && value.trim() !== '') {
+    const parsed = Number(value)
+    if (Number.isFinite(parsed)) return parsed
+  }
+  return null
+}
+
+export function formatUsdValue(value: number): string {
+  return new Intl.NumberFormat('en-US', {
+    style: 'currency',
+    currency: 'USD',
+    maximumFractionDigits: Math.abs(value) >= 100 ? 0 : 2,
+  }).format(value)
+}
+
+export function getSecondaryDisplayValue(input: {
+  rawAmount: string | number | null | undefined
+  decimals?: number
+  exchangeRate?: string | number | null
+  displayCurrency: 'native' | 'usd'
+}): string | null {
+  if (input.displayCurrency !== 'usd') return null
+
+  const exchangeRate = toFiniteNumber(input.exchangeRate)
+  if (exchangeRate == null || exchangeRate < 0) return null
+
+  const normalizedAmount = Number(formatUnits(input.rawAmount, input.decimals ?? 18, 8))
+  if (!Number.isFinite(normalizedAmount)) return null
+
+  return formatUsdValue(normalizedAmount * exchangeRate)
+}