fix: prevent user/group ID collision in currency preference store

src/components/Expense/ConvertibleBalance.tsx

@@ -25,6 +25,7 @@ interface ConvertibleBalanceProps {
   forceShowButton?: boolean;
   withText?: boolean;
   entityId?: number;
+  entityType?: 'group';
 }
 
 export const ConvertibleBalance: React.FC<ConvertibleBalanceProps> = ({
@@ -35,6 +36,7 @@ export const ConvertibleBalance: React.FC<ConvertibleBalanceProps> = ({
   forceShowButton = false,
   withText = false,
   entityId,
+  entityType,
 }) => {
   const { t } = useTranslationWithUtils();
   const [open, setOpen] = useState(false);
@@ -43,7 +45,7 @@ export const ConvertibleBalance: React.FC<ConvertibleBalanceProps> = ({
 
   const userDefaultCurrency = useCurrencyPreferenceStore((s) => s.userDefaultCurrency);
   const groupDefaultCurrency = useCurrencyPreferenceStore((s) =>
-    entityId ? s.groupDefaultCurrencies[entityId] : null,
+    entityId && entityType === 'group' ? s.groupDefaultCurrencies[entityId] : null,
   );
 
   // Available currencies from balances
@@ -60,14 +62,14 @@ export const ConvertibleBalance: React.FC<ConvertibleBalanceProps> = ({
     return res;
   }, [userDefaultCurrency, groupDefaultCurrency, overrideCurrencies, balances]);
 
-  const sessionPreference = useCurrencyPreferenceStore((s) => s.getPreference(entityId));
+  const sessionPreference = useCurrencyPreferenceStore((s) => s.getPreference(entityId, entityType));
   const setSelectedCurrency = useCurrencyPreferenceStore(
     (s) => (preference?: string) => s.setPreference(entityId, preference),
   );
   const clearPreference = useCurrencyPreferenceStore((s) => s.clearPreference);
 
   const selectedCurrency = useCurrencyPreferenceStore((s) => {
-    const preference = s.getPreference(entityId);
+    const preference = s.getPreference(entityId, entityType);
     if (preference === SHOW_ALL_VALUE || availableCurrencies.includes(preference ?? '')) {
       return preference;
     } else {
@@ -160,8 +162,6 @@ export const ConvertibleBalance: React.FC<ConvertibleBalanceProps> = ({
     return total;
   }, [shouldShowAll, balances, ratesQuery, selectedCurrency, t, setSelectedCurrency]);
 
-  console.log(selectedCurrency, groupDefaultCurrency);
-
   if (0 === balances.length) {
     return <AmountDisplay className={className} amount={0n} currency="USD" />;
   }

src/components/Expense/CumulatedBalances.tsx

@@ -7,11 +7,12 @@ import { useCurrencyPreferenceStore } from '~/store/currencyPreferenceStore';
 
 export const CumulatedBalances: React.FC<{
   entityId: number;
+  entityType?: 'group';
   balances?: { currency: string; amount: bigint }[];
-}> = ({ entityId, balances }) => {
+}> = ({ entityId, entityType, balances }) => {
   const { t } = useTranslationWithUtils();
 
-  const selectedCurrency = useCurrencyPreferenceStore((s) => s.getPreference(entityId));
+  const selectedCurrency = useCurrencyPreferenceStore((s) => s.getPreference(entityId, entityType));
 
   const allNonZeroCurrencies = useMemo(() => {
     const nonZeroBalances = balances?.filter((b) => b.amount !== 0n);
@@ -31,6 +32,7 @@ export const CumulatedBalances: React.FC<{
         <CumulatedBalanceDisplay
           prefix={`${t('ui.total_balance')}: `}
           entityId={entityId}
+          entityType={entityType}
           cumulatedBalances={balances}
           currencies={allNonZeroCurrencies}
         />
@@ -39,6 +41,7 @@ export const CumulatedBalances: React.FC<{
           <CumulatedBalanceDisplay
             prefix={`${t('actors.you')} ${t('ui.expense.you.lent')}`}
             entityId={entityId}
+            entityType={entityType}
             cumulatedBalances={youLent}
             className="text-positive"
             forceShowButton={allNonZeroCurrencies.length > 1}
@@ -47,6 +50,7 @@ export const CumulatedBalances: React.FC<{
           <CumulatedBalanceDisplay
             prefix={`${t('actors.you')} ${t('ui.expense.you.owe')}`}
             entityId={entityId}
+            entityType={entityType}
             className="text-negative"
             cumulatedBalances={youOwe}
             forceShowButton={allNonZeroCurrencies.length > 1}
@@ -61,13 +65,15 @@ export const CumulatedBalances: React.FC<{
 const CumulatedBalanceDisplay: React.FC<{
   prefix?: string;
   entityId: number;
+  entityType?: 'group';
   className?: string;
   cumulatedBalances?: { currency: string; amount: bigint }[];
   forceShowButton?: boolean;
   currencies: string[];
 }> = ({
   prefix = '',
   entityId,
+  entityType,
   className = '',
   cumulatedBalances,
   forceShowButton = false,
@@ -83,6 +89,7 @@ const CumulatedBalanceDisplay: React.FC<{
       <ConvertibleBalance
         balances={cumulatedBalances}
         entityId={entityId}
+        entityType={entityType}
         forceShowButton={forceShowButton}
         showMultiOption
         overrideCurrencies={currencies}

src/components/group/GroupMyBalance.tsx

@@ -70,7 +70,7 @@ const GroupMyBalance: React.FC<GroupMyBalanceProps> = ({
   return (
     <div className="flex gap-2">
       <div className="flex flex-col gap-2">
-        <CumulatedBalances entityId={groupId} balances={cumulatedBalances} />
+        <CumulatedBalances entityId={groupId} entityType="group" balances={cumulatedBalances} />
 
         {Object.entries(friendBalances)
           .slice(0, 2)

src/store/currencyPreferenceStore.ts

@@ -19,7 +19,7 @@ interface CurrencyPreferenceState {
   setUserDefaultCurrency: (currency: CurrencyCode | null) => void;
   setGroupDefaultCurrency: (groupId: number, currency: CurrencyCode | null) => void;
   setPreference: (key?: number | string, currency?: string) => void;
-  getPreference: (key?: number | string) => CurrencyPreference;
+  getPreference: (key?: number | string, entityType?: 'group') => CurrencyPreference;
   clearPreference: (key?: number | string) => void;
 }
 
@@ -50,9 +50,9 @@ export const useCurrencyPreferenceStore = create<CurrencyPreferenceState>()(
             [key]: isCurrencyCode(currency) ? currency : SHOW_ALL_VALUE,
           },
         })),
-      getPreference: (key = DEFAULT_KEY) =>
+      getPreference: (key = DEFAULT_KEY, entityType?: 'group') =>
         get().preferences[key] ||
-        (typeof key === 'number' && get().groupDefaultCurrencies[key]) ||
+        (entityType === 'group' && typeof key === 'number' && get().groupDefaultCurrencies[key]) ||
         get().userDefaultCurrency ||
         SHOW_ALL_VALUE,
       clearPreference: (key = DEFAULT_KEY) =>

src/tests/currencyPreferenceStore.test.ts

@@ -0,0 +1,67 @@
+import { SHOW_ALL_VALUE, useCurrencyPreferenceStore } from '~/store/currencyPreferenceStore';
+
+const resetStore = () =>
+  useCurrencyPreferenceStore.setState({
+    recentCurrencies: [],
+    userDefaultCurrency: null,
+    groupDefaultCurrencies: {},
+    preferences: {},
+  });
+
+beforeEach(() => {
+  sessionStorage.clear();
+  resetStore();
+});
+
+describe('getPreference – entity type isolation', () => {
+  it('returns userDefaultCurrency for a friend entity even when a group with the same id has a different default currency', () => {
+    const collidingId = 5;
+
+    // Simulate visiting the Groups page: group id=5 has USD as its default
+    useCurrencyPreferenceStore.getState().setGroupDefaultCurrency(collidingId, 'USD');
+    // User's own currency is EUR
+    useCurrencyPreferenceStore.getState().setUserDefaultCurrency('EUR');
+
+    // When rendering a friend balance entry (no entityType), USD must not leak in
+    const preference = useCurrencyPreferenceStore.getState().getPreference(collidingId);
+
+    expect(preference).toBe('EUR');
+    expect(preference).not.toBe('USD');
+  });
+
+  it('returns the group default currency when entityType is "group"', () => {
+    const groupId = 5;
+    useCurrencyPreferenceStore.getState().setGroupDefaultCurrency(groupId, 'USD');
+    useCurrencyPreferenceStore.getState().setUserDefaultCurrency('EUR');
+
+    const preference = useCurrencyPreferenceStore.getState().getPreference(groupId, 'group');
+
+    expect(preference).toBe('USD');
+  });
+
+  it('respects an explicit preference over all defaults for both entity types', () => {
+    const id = 7;
+    useCurrencyPreferenceStore.getState().setGroupDefaultCurrency(id, 'USD');
+    useCurrencyPreferenceStore.getState().setUserDefaultCurrency('EUR');
+    useCurrencyPreferenceStore.getState().setPreference(id, 'GBP');
+
+    expect(useCurrencyPreferenceStore.getState().getPreference(id)).toBe('GBP');
+    expect(useCurrencyPreferenceStore.getState().getPreference(id, 'group')).toBe('GBP');
+  });
+
+  it('falls back to SHOW_ALL when no preference, no group default (for group entity), and no user default', () => {
+    const preference = useCurrencyPreferenceStore.getState().getPreference(99, 'group');
+    expect(preference).toBe(SHOW_ALL_VALUE);
+  });
+
+  it('falls back to SHOW_ALL for a friend entity with no preference and no user default', () => {
+    useCurrencyPreferenceStore.getState().setGroupDefaultCurrency(3, 'USD');
+    const preference = useCurrencyPreferenceStore.getState().getPreference(3);
+    expect(preference).toBe(SHOW_ALL_VALUE);
+  });
+
+  it('uses the global (string) key when no entityId is provided', () => {
+    useCurrencyPreferenceStore.getState().setUserDefaultCurrency('JPY');
+    expect(useCurrencyPreferenceStore.getState().getPreference()).toBe('JPY');
+  });
+});