fix(split-meow): 混幣行程停止跨幣別錯誤加總與結算

.changeset/split-meow-mixed-currency-balances-guard.md

@@ -0,0 +1,5 @@
+---
+'@app/split-meow': patch
+---
+
+修正混幣行程的結算金額：當同一行程混用多種幣別時，總額、各人餘額與結算不再把不同幣別的數字直接相加，改為僅顯示混幣警告並隱藏「各人結算」區塊，避免誤導金額。編輯既有費用時改用該筆記帳當下的幣別符號。

apps/split-meow/src/components/HistoryTab.tsx

@@ -1,7 +1,15 @@
 import { useTranslation } from 'react-i18next';
+import { useShallow } from 'zustand/react/shallow';
 import { useStore, type Member, type ExpenseRecord } from '../store/useStore';
-import { formatAmount, getCurrencySymbol, formatKrwAsTwd } from '../config/currencies';
-import type { CurrencyCode } from '../config/currencies';
+import {
+  formatAmount,
+  getCurrencySymbol,
+  formatKrwAsTwd,
+  resolveExpenseCurrency,
+  resolveTripCurrency,
+  isMixedCurrencyTrip,
+  computeMemberBalances,
+} from '../config/currencies';
 import { format } from 'date-fns';
 import { useRef, useState } from 'react';
 import { cn } from '../lib/utils';
@@ -113,18 +121,20 @@ function ParticipantAvatars({
 
 export function HistoryTab() {
   const { t } = useTranslation();
-  const {
-    expenses,
-    members,
-    trips,
-    currentTripId,
-    deleteExpense,
-    updateExpenseNote,
-    updateExpense,
-    settledPayments,
-    toggleSettlement,
-    currency,
-  } = useStore();
+  const { expenses, members, trips, currentTripId, currency, settledPayments } = useStore(
+    useShallow((s) => ({
+      expenses: s.expenses,
+      members: s.members,
+      trips: s.trips,
+      currentTripId: s.currentTripId,
+      currency: s.currency,
+      settledPayments: s.settledPayments,
+    })),
+  );
+  const deleteExpense = useStore((s) => s.deleteExpense);
+  const updateExpenseNote = useStore((s) => s.updateExpenseNote);
+  const updateExpense = useStore((s) => s.updateExpense);
+  const toggleSettlement = useStore((s) => s.toggleSettlement);
   const [expandedId, setExpandedId] = useState<string | null>(null);
   const [expandedMemberId, setExpandedMemberId] = useState<string | null>(null);
   const [editingNoteId, setEditingNoteId] = useState<string | null>(null);
@@ -176,26 +186,13 @@ export function HistoryTab() {
         participantIds: e.participantIds.filter((id) => id in perPersonAmounts),
       };
     });
-  const totalSpent = tripExpenses.reduce((sum, e) => sum + e.totalAmount, 0);
-
-  // trip 主導幣別：採用該行程最舊一筆記錄的幣別（trip 建立時的幣別），
-  // 舊資料無幣別時 fallback 至當前全域幣別。彙總與結算統一以此幣別顯示。
-  const tripCurrency: CurrencyCode = tripExpenses[tripExpenses.length - 1]?.currency ?? currency;
-  // 取得單筆記錄的顯示幣別（優先使用記帳當下快照，舊資料 fallback 主導幣別）。
-  const expenseCurrency = (exp: ExpenseRecord): CurrencyCode => exp.currency ?? tripCurrency;
-  // 混幣行程：跨幣別直接相加的總額與結算為無效運算，改顯示警告而非誤導數字。
-  const isMixedCurrency = new Set(tripExpenses.map((exp) => expenseCurrency(exp))).size > 1;
-
-  // 計算各人餘額
-  const balances: Record<string, number> = {};
-  tripExpenses.forEach((exp) => {
-    balances[exp.paidBy] = (balances[exp.paidBy] ?? 0) + exp.totalAmount;
-    Object.entries(exp.perPersonAmounts).forEach(([memberId, amount]) => {
-      balances[memberId] = (balances[memberId] ?? 0) - amount;
-    });
-  });
 
-  const settlements = calculateSettlements({ ...balances });
+  const tripCurrency = resolveTripCurrency(tripExpenses, currency);
+  const expenseCurrency = (exp: ExpenseRecord) => resolveExpenseCurrency(exp, tripCurrency);
+  const isMixedCurrency = isMixedCurrencyTrip(tripExpenses, tripCurrency);
+  const totalSpent = isMixedCurrency ? 0 : tripExpenses.reduce((sum, e) => sum + e.totalAmount, 0);
+  const balances = isMixedCurrency ? {} : computeMemberBalances(tripExpenses);
+  const settlements = isMixedCurrency ? [] : calculateSettlements(balances);
 
   const startEditNote = (expId: string, currentNote: string, e: React.MouseEvent) => {
     e.stopPropagation();
@@ -407,7 +404,7 @@ export function HistoryTab() {
       )}
 
       {/* 各人結算 */}
-      {Object.keys(balances).length > 0 && (
+      {!isMixedCurrency && Object.keys(balances).length > 0 && (
         <section className="mb-10">
           <h3 className="text-xs font-medium uppercase tracking-widest text-outline px-2 mb-4">
             {t('history.balances')}
@@ -926,7 +923,8 @@ interface EditExpenseSheetProps {
 
 function EditExpenseSheet({ expense, members, onSave, onClose }: EditExpenseSheetProps) {
   const { t } = useTranslation();
-  const { currency } = useStore();
+  const globalCurrency = useStore((s) => s.currency);
+  const expenseCurrency = expense.currency ?? globalCurrency;
   const isEvenly = expense.type === 'split_evenly';
 
   const [totalInput, setTotalInput] = useState(
@@ -992,7 +990,7 @@ function EditExpenseSheet({ expense, members, onSave, onClose }: EditExpenseShee
         {isEvenly ? (
           <div className="flex items-center gap-3 bg-surface-container rounded-2xl px-4 py-3">
             <span className="text-on-surface-variant text-sm font-medium shrink-0">
-              {getCurrencySymbol(currency)}
+              {getCurrencySymbol(expenseCurrency)}
             </span>
             <input
               type="number"
@@ -1018,7 +1016,7 @@ function EditExpenseSheet({ expense, members, onSave, onClose }: EditExpenseShee
                     {m.name}
                   </span>
                   <span className="text-on-surface-variant text-sm shrink-0">
-                    {getCurrencySymbol(currency)}
+                    {getCurrencySymbol(expenseCurrency)}
                   </span>
                   <input
                     type="number"

apps/split-meow/src/components/__tests__/HomeAndHistorySmoke.test.tsx

@@ -244,8 +244,8 @@ describe('HistoryTab', () => {
     });
     renderWith(<HistoryTab />);
     expect(screen.getByText(i18n.t('history.mixed_currency_warning'))).toBeInTheDocument();
-    // 結算區塊標題不應出現：跨幣別結算為無效運算，不得顯示誤導金額。
     expect(screen.queryByText(i18n.t('history.settlements'))).not.toBeInTheDocument();
+    expect(screen.queryByText(i18n.t('history.balances'))).not.toBeInTheDocument();
   });
 
   it('單一幣別行程不顯示混幣警告', () => {

apps/split-meow/src/config/__tests__/currencies.test.ts

@@ -4,6 +4,10 @@ import {
   detectCurrencyFromTimezone,
   getCurrencySymbol,
   formatKrwAsTwd,
+  resolveExpenseCurrency,
+  resolveTripCurrency,
+  isMixedCurrencyTrip,
+  computeMemberBalances,
 } from '../currencies';
 
 describe('formatAmount', () => {
@@ -84,3 +88,31 @@ describe('formatKrwAsTwd', () => {
     expect(formatKrwAsTwd(30000, undefined)).toBeNull();
   });
 });
+
+describe('trip currency helpers', () => {
+  it('resolveTripCurrency 取最舊一筆的幣別', () => {
+    expect(resolveTripCurrency([{ currency: 'KRW' }, { currency: 'TWD' }], 'TWD')).toBe('TWD');
+  });
+
+  it('isMixedCurrencyTrip 偵測混幣行程', () => {
+    expect(isMixedCurrencyTrip([{ currency: 'TWD' }, { currency: 'KRW' }], 'TWD')).toBe(true);
+    expect(isMixedCurrencyTrip([{ currency: 'TWD' }, { currency: 'TWD' }], 'TWD')).toBe(false);
+  });
+
+  it('computeMemberBalances 僅加總同幣別 raw 金額', () => {
+    expect(
+      computeMemberBalances([
+        {
+          paidBy: 'a',
+          totalAmount: 100,
+          perPersonAmounts: { a: 50, b: 50 },
+        },
+      ]),
+    ).toEqual({ a: 50, b: -50 });
+  });
+
+  it('resolveExpenseCurrency 舊資料 fallback 行程幣別', () => {
+    expect(resolveExpenseCurrency({}, 'KRW')).toBe('KRW');
+    expect(resolveExpenseCurrency({ currency: 'TWD' }, 'KRW')).toBe('TWD');
+  });
+});

apps/split-meow/src/config/currencies.ts

@@ -37,6 +37,50 @@ export function getCurrencySymbol(currency: CurrencyCode): string {
   return CURRENCIES[currency].symbol;
 }
 
+/** 單筆費用的顯示幣別；舊資料缺欄位時 fallback 至行程主導幣別。 */
+export function resolveExpenseCurrency(
+  expense: { currency?: CurrencyCode },
+  tripCurrency: CurrencyCode,
+): CurrencyCode {
+  return expense.currency ?? tripCurrency;
+}
+
+/** 行程主導幣別：最舊一筆記帳的幣別快照，舊資料 fallback 全域幣別。 */
+export function resolveTripCurrency(
+  expenses: { currency?: CurrencyCode }[],
+  globalCurrency: CurrencyCode,
+): CurrencyCode {
+  return expenses[expenses.length - 1]?.currency ?? globalCurrency;
+}
+
+/** 行程是否混用多種幣別；混幣時不可加總或結算。 */
+export function isMixedCurrencyTrip(
+  expenses: { currency?: CurrencyCode }[],
+  tripCurrency: CurrencyCode,
+): boolean {
+  if (expenses.length === 0) return false;
+  const codes = new Set(expenses.map((exp) => resolveExpenseCurrency(exp, tripCurrency)));
+  return codes.size > 1;
+}
+
+/** 同幣別行程的成員餘額；僅在 `isMixedCurrencyTrip` 為 false 時有意義。 */
+export function computeMemberBalances(
+  expenses: {
+    paidBy: string;
+    totalAmount: number;
+    perPersonAmounts: Record<string, number>;
+  }[],
+): Record<string, number> {
+  const balances: Record<string, number> = {};
+  for (const exp of expenses) {
+    balances[exp.paidBy] = (balances[exp.paidBy] ?? 0) + exp.totalAmount;
+    for (const [memberId, amount] of Object.entries(exp.perPersonAmounts)) {
+      balances[memberId] = (balances[memberId] ?? 0) - amount;
+    }
+  }
+  return balances;
+}
+
 /**
  * 將 KRW 金額依匯率快照換算為 TWD 顯示字串（用於 KRW 記帳時的副標）。
  * rate 為 1 TWD = rate KRW（賣出價）；rate 無效時回傳 null 表示無法換算。

apps/split-meow/src/i18n.ts

@@ -1,6 +1,5 @@
 /**
- * i18n 初始化設定
- * 支援語言：繁體中文（預設）、英文、韓文、日文
+ * i18n 初始化：繁中（預設）、英文、韓文、日文。
  */
 import i18n from 'i18next';
 import { initReactI18next } from 'react-i18next';

apps/split-meow/src/store/useStore.ts

@@ -105,7 +105,6 @@ const INITIAL_SEEDS = {
   m2: 'split-meow-luna',
 };
 
-/** ロケール別のランダム名生成素材 */
 const NAME_PARTS: Record<string, { prefixes: string[]; suffixes: string[] }> = {
   'zh-TW': {
     prefixes: ['奶油', '布丁', '麻糬', '棉花', '糰子', '可可', '芝麻', '蜜桃', '焦糖', '雲朵'],
@@ -270,7 +269,6 @@ export const useStore = create<AppState>()(
             note: state.expenseNote.trim(),
             ...(state.expenseCategory ? { category: state.expenseCategory } : {}),
             createdAt: Date.now(),
-            // 記帳當下的幣別與匯率快照，確保歷史金額不受日後切換幣別影響並可回溯換算
             currency: state.currency,
             exchangeRateKrwPerTwd: state.krwPerTwd,
           };