Merge branch 'fix/calculation-accuracy' into main

Combines the decimal migration (int cents → decimal.Decimal via
shopspring/decimal) with main's handler refactor (split space.go into
domain handlers, WithTx/Paginate helpers, recurring deposit removal).

- Repository layer: WithTx pattern + decimal column names/types
- Handler layer: decimal arithmetic (.Sub/.Add) instead of int operators
- Models: deprecated amount_cents fields kept for SELECT * compatibility
- INSERT statements: old columns set to literal 0 for NOT NULL constraints

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

internal/handler/account_handler.go

@@ -73,7 +73,7 @@ func (h *AccountHandler) AccountsPage(w http.ResponseWriter, r *http.Request) {
 		return
 	}
 
-	availableBalance := totalBalance - totalAllocated
+	availableBalance := totalBalance.Sub(totalAllocated)
 
 	transfers, totalPages, err := h.accountService.GetTransfersForSpacePaginated(spaceID, 1)
 	if err != nil {
@@ -113,7 +113,7 @@ func (h *AccountHandler) CreateAccount(w http.ResponseWriter, r *http.Request) {
 
 	acctWithBalance := model.MoneyAccountWithBalance{
 		MoneyAccount: *account,
-		BalanceCents: 0,
+		Balance:      decimal.Zero,
 	}
 
 	ui.Render(w, r, moneyaccount.AccountCard(spaceID, &acctWithBalance))
@@ -157,7 +157,7 @@ func (h *AccountHandler) UpdateAccount(w http.ResponseWriter, r *http.Request) {
 
 	acctWithBalance := model.MoneyAccountWithBalance{
 		MoneyAccount: *updatedAccount,
-		BalanceCents: balance,
+		Balance:      balance,
 	}
 
 	ui.Render(w, r, moneyaccount.AccountCard(spaceID, &acctWithBalance))
@@ -188,7 +188,7 @@ func (h *AccountHandler) DeleteAccount(w http.ResponseWriter, r *http.Request) {
 		slog.Error("failed to get total allocated", "error", err, "space_id", spaceID)
 	}
 
-	ui.Render(w, r, moneyaccount.BalanceSummaryCard(spaceID, totalBalance, totalBalance-totalAllocated, true))
+	ui.Render(w, r, moneyaccount.BalanceSummaryCard(spaceID, totalBalance, totalBalance.Sub(totalAllocated), true))
 	ui.RenderToast(w, r, toast.Toast(toast.Props{
 		Title:       "Account deleted",
 		Variant:     toast.VariantSuccess,
@@ -221,7 +221,7 @@ func (h *AccountHandler) CreateTransfer(w http.ResponseWriter, r *http.Request)
 		ui.RenderError(w, r, "Invalid amount", http.StatusUnprocessableEntity)
 		return
 	}
-	amountCents := int(amountDecimal.Mul(decimal.NewFromInt(100)).IntPart())
+	amount := amountDecimal
 
 	// Calculate available space balance for deposit validation
 	totalBalance, err := h.expenseService.GetBalanceForSpace(spaceID)
@@ -236,11 +236,11 @@ func (h *AccountHandler) CreateTransfer(w http.ResponseWriter, r *http.Request)
 		http.Error(w, "Internal Server Error", http.StatusInternalServerError)
 		return
 	}
-	availableBalance := totalBalance - totalAllocated
+	availableBalance := totalBalance.Sub(totalAllocated)
 
 	// Validate balance limits before creating transfer
-	if direction == model.TransferDirectionDeposit && amountCents > availableBalance {
-		ui.RenderError(w, r, fmt.Sprintf("Insufficient available balance. You can deposit up to $%.2f.", float64(availableBalance)/100.0), http.StatusUnprocessableEntity)
+	if direction == model.TransferDirectionDeposit && amount.GreaterThan(availableBalance) {
+		ui.RenderError(w, r, fmt.Sprintf("Insufficient available balance. You can deposit up to %s.", model.FormatMoney(availableBalance)), http.StatusUnprocessableEntity)
 		return
 	}
 
@@ -251,15 +251,15 @@ func (h *AccountHandler) CreateTransfer(w http.ResponseWriter, r *http.Request)
 			http.Error(w, "Internal Server Error", http.StatusInternalServerError)
 			return
 		}
-		if amountCents > acctBalance {
-			ui.RenderError(w, r, fmt.Sprintf("Insufficient account balance. You can withdraw up to $%.2f.", float64(acctBalance)/100.0), http.StatusUnprocessableEntity)
+		if amount.GreaterThan(acctBalance) {
+			ui.RenderError(w, r, fmt.Sprintf("Insufficient account balance. You can withdraw up to %s.", model.FormatMoney(acctBalance)), http.StatusUnprocessableEntity)
 			return
 		}
 	}
 
 	_, err = h.accountService.CreateTransfer(service.CreateTransferDTO{
 		AccountID: accountID,
-		Amount:    amountCents,
+		Amount:    amount,
 		Direction: direction,
 		Note:      note,
 		CreatedBy: user.ID,
@@ -281,12 +281,12 @@ func (h *AccountHandler) CreateTransfer(w http.ResponseWriter, r *http.Request)
 	account, _ := h.accountService.GetAccount(accountID)
 	acctWithBalance := model.MoneyAccountWithBalance{
 		MoneyAccount: *account,
-		BalanceCents: accountBalance,
+		Balance:      accountBalance,
 	}
 
 	// Recalculate available balance after transfer
 	totalAllocated, _ = h.accountService.GetTotalAllocatedForSpace(spaceID)
-	newAvailable := totalBalance - totalAllocated
+	newAvailable := totalBalance.Sub(totalAllocated)
 
 	w.Header().Set("HX-Trigger", "transferSuccess")
 	ui.Render(w, r, moneyaccount.AccountCard(spaceID, &acctWithBalance, true))
@@ -323,14 +323,14 @@ func (h *AccountHandler) DeleteTransfer(w http.ResponseWriter, r *http.Request)
 	account, _ := h.accountService.GetAccount(accountID)
 	acctWithBalance := model.MoneyAccountWithBalance{
 		MoneyAccount: *account,
-		BalanceCents: accountBalance,
+		Balance:      accountBalance,
 	}
 
 	totalBalance, _ := h.expenseService.GetBalanceForSpace(spaceID)
 	totalAllocated, _ := h.accountService.GetTotalAllocatedForSpace(spaceID)
 
 	ui.Render(w, r, moneyaccount.AccountCard(spaceID, &acctWithBalance, true))
-	ui.Render(w, r, moneyaccount.BalanceSummaryCard(spaceID, totalBalance, totalBalance-totalAllocated, true))
+	ui.Render(w, r, moneyaccount.BalanceSummaryCard(spaceID, totalBalance, totalBalance.Sub(totalAllocated), true))
 
 	transfers, transferTotalPages, _ := h.accountService.GetTransfersForSpacePaginated(spaceID, 1)
 	ui.Render(w, r, moneyaccount.TransferHistoryContent(spaceID, transfers, 1, transferTotalPages, true))

internal/handler/budget_handler.go

@@ -106,7 +106,7 @@ func (h *BudgetHandler) CreateBudget(w http.ResponseWriter, r *http.Request) {
 		ui.RenderError(w, r, "Invalid amount.", http.StatusUnprocessableEntity)
 		return
 	}
-	amountCents := int(amountDecimal.Mul(decimal.NewFromInt(100)).IntPart())
+	amount := amountDecimal
 
 	startDate, err := time.Parse("2006-01-02", startDateStr)
 	if err != nil {
@@ -127,7 +127,7 @@ func (h *BudgetHandler) CreateBudget(w http.ResponseWriter, r *http.Request) {
 	_, err = h.budgetService.CreateBudget(service.CreateBudgetDTO{
 		SpaceID:   spaceID,
 		TagIDs:    tagIDs,
-		Amount:    amountCents,
+		Amount:    amount,
 		Period:    model.BudgetPeriod(periodStr),
 		StartDate: startDate,
 		EndDate:   endDate,
@@ -186,7 +186,7 @@ func (h *BudgetHandler) UpdateBudget(w http.ResponseWriter, r *http.Request) {
 		ui.RenderError(w, r, "Invalid amount.", http.StatusUnprocessableEntity)
 		return
 	}
-	amountCents := int(amountDecimal.Mul(decimal.NewFromInt(100)).IntPart())
+	amount := amountDecimal
 
 	startDate, err := time.Parse("2006-01-02", startDateStr)
 	if err != nil {
@@ -207,7 +207,7 @@ func (h *BudgetHandler) UpdateBudget(w http.ResponseWriter, r *http.Request) {
 	_, err = h.budgetService.UpdateBudget(service.UpdateBudgetDTO{
 		ID:        budgetID,
 		TagIDs:    tagIDs,
-		Amount:    amountCents,
+		Amount:    amount,
 		Period:    model.BudgetPeriod(periodStr),
 		StartDate: startDate,
 		EndDate:   endDate,

internal/handler/expense_handler.go

@@ -81,9 +81,9 @@ func (h *ExpenseHandler) ExpensesPage(w http.ResponseWriter, r *http.Request) {
 	totalAllocated, err := h.accountService.GetTotalAllocatedForSpace(spaceID)
 	if err != nil {
 		slog.Error("failed to get total allocated", "error", err, "space_id", spaceID)
-		totalAllocated = 0
+		totalAllocated = decimal.Zero
 	}
-	balance -= totalAllocated
+	balance = balance.Sub(totalAllocated)
 
 	tags, err := h.tagService.GetTagsForSpace(spaceID)
 	if err != nil {
@@ -147,7 +147,7 @@ func (h *ExpenseHandler) CreateExpense(w http.ResponseWriter, r *http.Request) {
 		ui.RenderError(w, r, "Invalid amount format.", http.StatusUnprocessableEntity)
 		return
 	}
-	amountCents := int(amountDecimal.Mul(decimal.NewFromInt(100)).IntPart())
+	amount := amountDecimal
 
 	date, err := time.Parse("2006-01-02", dateStr)
 	if err != nil {
@@ -220,7 +220,7 @@ func (h *ExpenseHandler) CreateExpense(w http.ResponseWriter, r *http.Request) {
 		SpaceID:         spaceID,
 		UserID:          user.ID,
 		Description:     description,
-		Amount:          amountCents,
+		Amount:          amount,
 		Type:            expenseType,
 		Date:            date,
 		TagIDs:          finalTagIDs,
@@ -263,9 +263,9 @@ func (h *ExpenseHandler) CreateExpense(w http.ResponseWriter, r *http.Request) {
 	totalAllocated, err := h.accountService.GetTotalAllocatedForSpace(spaceID)
 	if err != nil {
 		slog.Error("failed to get total allocated", "error", err, "space_id", spaceID)
-		totalAllocated = 0
+		totalAllocated = decimal.Zero
 	}
-	balance -= totalAllocated
+	balance = balance.Sub(totalAllocated)
 
 	// Return the full paginated list for page 1 so the new expense appears
 	expenses, totalPages, err := h.expenseService.GetExpensesWithTagsAndMethodsForSpacePaginated(spaceID, 1)
@@ -317,7 +317,7 @@ func (h *ExpenseHandler) UpdateExpense(w http.ResponseWriter, r *http.Request) {
 		ui.RenderError(w, r, "Invalid amount format.", http.StatusUnprocessableEntity)
 		return
 	}
-	amountCents := int(amountDecimal.Mul(decimal.NewFromInt(100)).IntPart())
+	amount := amountDecimal
 
 	date, err := time.Parse("2006-01-02", dateStr)
 	if err != nil {
@@ -377,7 +377,7 @@ func (h *ExpenseHandler) UpdateExpense(w http.ResponseWriter, r *http.Request) {
 		ID:              expenseID,
 		SpaceID:         spaceID,
 		Description:     description,
-		Amount:          amountCents,
+		Amount:          amount,
 		Type:            expenseType,
 		Date:            date,
 		TagIDs:          finalTagIDs,
@@ -407,9 +407,9 @@ func (h *ExpenseHandler) UpdateExpense(w http.ResponseWriter, r *http.Request) {
 	totalAllocated, err := h.accountService.GetTotalAllocatedForSpace(spaceID)
 	if err != nil {
 		slog.Error("failed to get total allocated", "error", err, "space_id", spaceID)
-		totalAllocated = 0
+		totalAllocated = decimal.Zero
 	}
-	balance -= totalAllocated
+	balance = balance.Sub(totalAllocated)
 
 	methods, _ := h.methodService.GetMethodsForSpace(spaceID)
 	updatedTags, _ := h.tagService.GetTagsForSpace(spaceID)
@@ -438,9 +438,9 @@ func (h *ExpenseHandler) DeleteExpense(w http.ResponseWriter, r *http.Request) {
 	totalAllocated, err := h.accountService.GetTotalAllocatedForSpace(spaceID)
 	if err != nil {
 		slog.Error("failed to get total allocated", "error", err, "space_id", spaceID)
-		totalAllocated = 0
+		totalAllocated = decimal.Zero
 	}
-	balance -= totalAllocated
+	balance = balance.Sub(totalAllocated)
 
 	ui.Render(w, r, expense.BalanceCard(spaceID, balance, totalAllocated, true))
 	ui.RenderToast(w, r, toast.Toast(toast.Props{
@@ -485,9 +485,9 @@ func (h *ExpenseHandler) GetBalanceCard(w http.ResponseWriter, r *http.Request)
 	totalAllocated, err := h.accountService.GetTotalAllocatedForSpace(spaceID)
 	if err != nil {
 		slog.Error("failed to get total allocated", "error", err, "space_id", spaceID)
-		totalAllocated = 0
+		totalAllocated = decimal.Zero
 	}
-	balance -= totalAllocated
+	balance = balance.Sub(totalAllocated)
 
 	ui.Render(w, r, expense.BalanceCard(spaceID, balance, totalAllocated, false))
 }

internal/handler/recurring_handler.go

@@ -107,7 +107,7 @@ func (h *RecurringHandler) CreateRecurringExpense(w http.ResponseWriter, r *http
 		ui.RenderError(w, r, "Invalid amount format.", http.StatusUnprocessableEntity)
 		return
 	}
-	amountCents := int(amountDecimal.Mul(decimal.NewFromInt(100)).IntPart())
+	amount := amountDecimal
 
 	startDate, err := time.Parse("2006-01-02", startDateStr)
 	if err != nil {
@@ -176,7 +176,7 @@ func (h *RecurringHandler) CreateRecurringExpense(w http.ResponseWriter, r *http
 		SpaceID:         spaceID,
 		UserID:          user.ID,
 		Description:     description,
-		Amount:          amountCents,
+		Amount:          amount,
 		Type:            expenseType,
 		PaymentMethodID: paymentMethodID,
 		Frequency:       frequency,
@@ -235,7 +235,7 @@ func (h *RecurringHandler) UpdateRecurringExpense(w http.ResponseWriter, r *http
 		ui.RenderError(w, r, "Invalid amount.", http.StatusUnprocessableEntity)
 		return
 	}
-	amountCents := int(amountDecimal.Mul(decimal.NewFromInt(100)).IntPart())
+	amount := amountDecimal
 
 	startDate, err := time.Parse("2006-01-02", startDateStr)
 	if err != nil {
@@ -290,7 +290,7 @@ func (h *RecurringHandler) UpdateRecurringExpense(w http.ResponseWriter, r *http
 	updated, err := h.recurringService.UpdateRecurringExpense(service.UpdateRecurringExpenseDTO{
 		ID:              recurringID,
 		Description:     description,
-		Amount:          amountCents,
+		Amount:          amount,
 		Type:            model.ExpenseType(typeStr),
 		PaymentMethodID: paymentMethodID,
 		Frequency:       model.Frequency(frequencyStr),

internal/handler/space.go

@@ -7,6 +7,8 @@ import (
 	"strings"
 	"time"
 
+	"github.com/shopspring/decimal"
+
 	"git.juancwu.dev/juancwu/budgit/internal/ctxkeys"
 	"git.juancwu.dev/juancwu/budgit/internal/model"
 	"git.juancwu.dev/juancwu/budgit/internal/service"
@@ -112,9 +114,9 @@ func (h *SpaceHandler) OverviewPage(w http.ResponseWriter, r *http.Request) {
 	allocated, err := h.accountService.GetTotalAllocatedForSpace(spaceID)
 	if err != nil {
 		slog.Error("failed to get total allocated", "error", err, "space_id", spaceID)
-		allocated = 0
+		allocated = decimal.Zero
 	}
-	balance -= allocated
+	balance = balance.Sub(allocated)
 
 	// This month's report
 	now := time.Now()

internal/handler/space_loans.go

@@ -62,8 +62,6 @@ func (h *SpaceHandler) CreateLoan(w http.ResponseWriter, r *http.Request) {
 		w.WriteHeader(http.StatusUnprocessableEntity)
 		return
 	}
-	amountCents := int(amount.Mul(decimal.NewFromInt(100)).IntPart())
-
 	interestStr := r.FormValue("interest_rate")
 	var interestBps int
 	if interestStr != "" {
@@ -93,7 +91,7 @@ func (h *SpaceHandler) CreateLoan(w http.ResponseWriter, r *http.Request) {
 		UserID:          user.ID,
 		Name:            name,
 		Description:     description,
-		OriginalAmount:  amountCents,
+		OriginalAmount:  amount,
 		InterestRateBps: interestBps,
 		StartDate:       startDate,
 		EndDate:         endDate,
@@ -165,7 +163,7 @@ func (h *SpaceHandler) LoanDetailPage(w http.ResponseWriter, r *http.Request) {
 	balance, err := h.expenseService.GetBalanceForSpace(spaceID)
 	if err != nil {
 		slog.Error("failed to get balance", "error", err)
-		balance = 0
+		balance = decimal.Zero
 	}
 
 	ui.Render(w, r, pages.SpaceLoanDetailPage(space, loan, receipts, page, totalPages, recurringReceipts, accounts, balance))
@@ -190,8 +188,6 @@ func (h *SpaceHandler) UpdateLoan(w http.ResponseWriter, r *http.Request) {
 		w.WriteHeader(http.StatusUnprocessableEntity)
 		return
 	}
-	amountCents := int(amount.Mul(decimal.NewFromInt(100)).IntPart())
-
 	interestStr := r.FormValue("interest_rate")
 	var interestBps int
 	if interestStr != "" {
@@ -220,7 +216,7 @@ func (h *SpaceHandler) UpdateLoan(w http.ResponseWriter, r *http.Request) {
 		ID:              loanID,
 		Name:            name,
 		Description:     description,
-		OriginalAmount:  amountCents,
+		OriginalAmount:  amount,
 		InterestRateBps: interestBps,
 		StartDate:       startDate,
 		EndDate:         endDate,
@@ -267,8 +263,6 @@ func (h *SpaceHandler) CreateReceipt(w http.ResponseWriter, r *http.Request) {
 		w.WriteHeader(http.StatusUnprocessableEntity)
 		return
 	}
-	totalAmountCents := int(amount.Mul(decimal.NewFromInt(100)).IntPart())
-
 	dateStr := r.FormValue("date")
 	date, err := time.Parse("2006-01-02", dateStr)
 	if err != nil {
@@ -288,7 +282,7 @@ func (h *SpaceHandler) CreateReceipt(w http.ResponseWriter, r *http.Request) {
 		SpaceID:        spaceID,
 		UserID:         user.ID,
 		Description:    description,
-		TotalAmount:    totalAmountCents,
+		TotalAmount:    amount,
 		Date:           date,
 		FundingSources: fundingSources,
 	}
@@ -320,8 +314,6 @@ func (h *SpaceHandler) UpdateReceipt(w http.ResponseWriter, r *http.Request) {
 		w.WriteHeader(http.StatusUnprocessableEntity)
 		return
 	}
-	totalAmountCents := int(amount.Mul(decimal.NewFromInt(100)).IntPart())
-
 	dateStr := r.FormValue("date")
 	date, err := time.Parse("2006-01-02", dateStr)
 	if err != nil {
@@ -340,7 +332,7 @@ func (h *SpaceHandler) UpdateReceipt(w http.ResponseWriter, r *http.Request) {
 		SpaceID:        spaceID,
 		UserID:         user.ID,
 		Description:    description,
-		TotalAmount:    totalAmountCents,
+		TotalAmount:    amount,
 		Date:           date,
 		FundingSources: fundingSources,
 	}
@@ -405,8 +397,6 @@ func (h *SpaceHandler) CreateRecurringReceipt(w http.ResponseWriter, r *http.Req
 		w.WriteHeader(http.StatusUnprocessableEntity)
 		return
 	}
-	totalAmountCents := int(amount.Mul(decimal.NewFromInt(100)).IntPart())
-
 	frequency := model.Frequency(r.FormValue("frequency"))
 
 	startDateStr := r.FormValue("start_date")
@@ -436,7 +426,7 @@ func (h *SpaceHandler) CreateRecurringReceipt(w http.ResponseWriter, r *http.Req
 		SpaceID:        spaceID,
 		UserID:         user.ID,
 		Description:    description,
-		TotalAmount:    totalAmountCents,
+		TotalAmount:    amount,
 		Frequency:      frequency,
 		StartDate:      startDate,
 		EndDate:        endDate,
@@ -468,8 +458,6 @@ func (h *SpaceHandler) UpdateRecurringReceipt(w http.ResponseWriter, r *http.Req
 		w.WriteHeader(http.StatusUnprocessableEntity)
 		return
 	}
-	totalAmountCents := int(amount.Mul(decimal.NewFromInt(100)).IntPart())
-
 	frequency := model.Frequency(r.FormValue("frequency"))
 
 	startDateStr := r.FormValue("start_date")
@@ -497,7 +485,7 @@ func (h *SpaceHandler) UpdateRecurringReceipt(w http.ResponseWriter, r *http.Req
 	dto := service.UpdateRecurringReceiptDTO{
 		ID:             recurringReceiptID,
 		Description:    description,
-		TotalAmount:    totalAmountCents,
+		TotalAmount:    amount,
 		Frequency:      frequency,
 		StartDate:      startDate,
 		EndDate:        endDate,
@@ -570,11 +558,9 @@ func parseFundingSources(r *http.Request) ([]service.FundingSourceDTO, error) {
 		if err != nil || amount.LessThanOrEqual(decimal.Zero) {
 			return nil, fmt.Errorf("invalid funding source amount")
 		}
-		amountCents := int(amount.Mul(decimal.NewFromInt(100)).IntPart())
-
 		src := service.FundingSourceDTO{
 			SourceType: model.FundingSourceType(srcType),
-			Amount:     amountCents,
+			Amount:     amount,
 		}
 
 		if srcType == string(model.FundingSourceAccount) {