feat: transfer funds between accounts

internal/handler/space.go

@@ -329,12 +329,13 @@ func (h *spaceHandler) SpaceAccountPage(w http.ResponseWriter, r *http.Request)
 	}
 
 	ui.Render(w, r, pages.SpaceAccountPage(pages.SpaceAccountPageProps{
-		SpaceID:            spaceID,
-		SpaceName:          space.Name,
-		AccountID:          accountID,
-		AccountName:        account.Name,
-		AccountBalance:     account.Balance,
-		RecentTransactions: recent,
+		SpaceID:                  spaceID,
+		SpaceName:                space.Name,
+		AccountID:                accountID,
+		AccountName:              account.Name,
+		AccountBalance:           account.Balance,
+		RecentTransactions:       recent,
+		NonEditableTransactionIDs: h.nonEditableTransactionIDs(recent),
 	}))
 }
 
@@ -392,18 +393,40 @@ func (h *spaceHandler) SpaceAccountTransactionsPage(w http.ResponseWriter, r *ht
 	}
 
 	ui.Render(w, r, pages.SpaceAccountTransactionsPage(pages.SpaceAccountTransactionsPageProps{
-		SpaceID:      spaceID,
-		SpaceName:    space.Name,
-		AccountID:    accountID,
-		AccountName:  account.Name,
-		Transactions: txns,
-		CurrentPage:  page,
-		TotalPages:   totalPages,
-		TotalCount:   total,
-		PerPage:      perPage,
+		SpaceID:                  spaceID,
+		SpaceName:                space.Name,
+		AccountID:                accountID,
+		AccountName:              account.Name,
+		Transactions:             txns,
+		NonEditableTransactionIDs: h.nonEditableTransactionIDs(txns),
+		CurrentPage:              page,
+		TotalPages:               totalPages,
+		TotalCount:               total,
+		PerPage:                  perPage,
 	}))
 }
 
+// nonEditableTransactionIDs returns the subset of the given transactions that
+// are part of a transfer pair and therefore not editable. Returns an empty
+// (non-nil) map on error so list rendering still works — failure here just
+// means stale Edit buttons appear; the service layer will still refuse the
+// edit, so it's a UX degradation rather than a correctness issue.
+func (h *spaceHandler) nonEditableTransactionIDs(txns []*model.Transaction) map[string]bool {
+	if len(txns) == 0 {
+		return nil
+	}
+	ids := make([]string, len(txns))
+	for i, t := range txns {
+		ids[i] = t.ID
+	}
+	hits, err := h.transactionService.TransferIDsIn(ids)
+	if err != nil {
+		slog.Error("failed to look up transfer ids", "error", err)
+		return map[string]bool{}
+	}
+	return hits
+}
+
 func (h *spaceHandler) SpaceSettingsPage(w http.ResponseWriter, r *http.Request) {
 	spaceID := r.PathValue("spaceID")
 
@@ -1042,6 +1065,26 @@ func (h *spaceHandler) SpaceTransactionPage(w http.ResponseWriter, r *http.Reque
 		}
 	}
 
+	relatedID, err := h.transactionService.GetRelatedTransactionID(transactionID)
+	if err != nil {
+		slog.Error("failed to load related transaction", "error", err, "transaction_id", transactionID)
+		relatedID = ""
+	}
+	var relatedTxn *model.Transaction
+	var relatedAccount *model.Account
+	if relatedID != "" {
+		relatedTxn, err = h.transactionService.GetTransaction(relatedID)
+		if err != nil {
+			slog.Error("failed to load related transaction details", "error", err, "related_id", relatedID)
+		} else {
+			relatedAccount, err = h.accountService.GetAccount(relatedTxn.AccountID)
+			if err != nil {
+				slog.Error("failed to load related transaction account", "error", err, "account_id", relatedTxn.AccountID)
+				relatedAccount = nil
+			}
+		}
+	}
+
 	recentLogs, err := h.txAuditLogService.List(transactionID, 5, 0)
 	if err != nil {
 		slog.Error("failed to load transaction audit logs", "error", err, "transaction_id", transactionID)
@@ -1054,14 +1097,16 @@ func (h *spaceHandler) SpaceTransactionPage(w http.ResponseWriter, r *http.Reque
 	}
 
 	ui.Render(w, r, pages.SpaceTransactionPage(pages.SpaceTransactionPageProps{
-		SpaceID:         spaceID,
-		SpaceName:       space.Name,
-		AccountID:       accountID,
-		AccountName:     account.Name,
-		Transaction:     txn,
-		CategoryName:    categoryName,
-		RecentAuditLogs: recentLogs,
-		AuditLogCount:   logCount,
+		SpaceID:            spaceID,
+		SpaceName:          space.Name,
+		AccountID:          accountID,
+		AccountName:        account.Name,
+		Transaction:        txn,
+		CategoryName:       categoryName,
+		RecentAuditLogs:    recentLogs,
+		AuditLogCount:      logCount,
+		RelatedTransaction: relatedTxn,
+		RelatedAccount:     relatedAccount,
 	}))
 }
 
@@ -1211,6 +1256,22 @@ func (h *spaceHandler) SpaceEditTransactionPage(w http.ResponseWriter, r *http.R
 		return
 	}
 
+	// Transfers must be edited as a pair; refuse the edit page entirely.
+	relatedID, err := h.transactionService.GetRelatedTransactionID(transactionID)
+	if err != nil {
+		slog.Error("failed to check transfer linkage", "error", err, "transaction_id", transactionID)
+	}
+	if relatedID != "" {
+		redirectTo := routeurl.URL(
+			"page.app.spaces.space.accounts.account.transactions.transaction",
+			"spaceID", spaceID,
+			"accountID", accountID,
+			"transactionID", transactionID,
+		)
+		http.Redirect(w, r, redirectTo, http.StatusSeeOther)
+		return
+	}
+
 	space, err := h.spaceService.GetSpace(spaceID)
 	if err != nil {
 		slog.Error("failed to load space", "error", err, "space_id", spaceID)
@@ -1286,6 +1347,15 @@ func (h *spaceHandler) HandleEditTransaction(w http.ResponseWriter, r *http.Requ
 		return
 	}
 
+	// Defense in depth — the edit page redirects away for transfers, but a
+	// hand-crafted POST shouldn't be able to bypass it.
+	if relatedID, err := h.transactionService.GetRelatedTransactionID(transactionID); err != nil {
+		slog.Error("failed to check transfer linkage", "error", err, "transaction_id", transactionID)
+	} else if relatedID != "" {
+		ui.RenderError(w, r, "Transfer transactions cannot be edited.", http.StatusBadRequest)
+		return
+	}
+
 	titleInput := strings.TrimSpace(r.FormValue("title"))
 	amountInput := strings.TrimSpace(r.FormValue("amount"))
 	dateInput := strings.TrimSpace(r.FormValue("date"))
@@ -1431,6 +1501,183 @@ func (h *spaceHandler) HandleEditTransaction(w http.ResponseWriter, r *http.Requ
 	w.WriteHeader(http.StatusOK)
 }
 
+func (h *spaceHandler) SpaceCreateTransferPage(w http.ResponseWriter, r *http.Request) {
+	spaceID := r.PathValue("spaceID")
+	accountID := r.PathValue("accountID")
+
+	account, err := h.accountService.GetAccount(accountID)
+	if err != nil || account.SpaceID != spaceID {
+		ui.Render(w, r, pages.NotFound())
+		return
+	}
+
+	space, err := h.spaceService.GetSpace(spaceID)
+	if err != nil {
+		slog.Error("failed to load space", "error", err, "space_id", spaceID)
+		ui.RenderError(w, r, "Failed to load page", http.StatusInternalServerError)
+		return
+	}
+
+	dests, err := h.transferDestinations(spaceID, accountID)
+	if err != nil {
+		slog.Error("failed to load destination accounts", "error", err, "space_id", spaceID)
+		ui.RenderError(w, r, "Failed to load page", http.StatusInternalServerError)
+		return
+	}
+
+	ui.Render(w, r, pages.SpaceCreateTransferPage(pages.SpaceCreateTransferPageProps{
+		SpaceID:     spaceID,
+		SpaceName:   space.Name,
+		AccountID:   accountID,
+		AccountName: account.Name,
+		Form: forms.CreateTransferProps{
+			SpaceID:         spaceID,
+			SourceAccountID: accountID,
+			DestAccounts:    dests,
+			Date:            time.Now().Format("2006-01-02"),
+		},
+	}))
+}
+
+func (h *spaceHandler) HandleCreateTransfer(w http.ResponseWriter, r *http.Request) {
+	spaceID := r.PathValue("spaceID")
+	accountID := r.PathValue("accountID")
+
+	source, err := h.accountService.GetAccount(accountID)
+	if err != nil || source.SpaceID != spaceID {
+		ui.RenderError(w, r, "Account not found", http.StatusNotFound)
+		return
+	}
+
+	dests, err := h.transferDestinations(spaceID, accountID)
+	if err != nil {
+		slog.Error("failed to load destination accounts", "error", err, "space_id", spaceID)
+		ui.RenderError(w, r, "Failed to load form", http.StatusInternalServerError)
+		return
+	}
+
+	titleInput := strings.TrimSpace(r.FormValue("title"))
+	amountInput := strings.TrimSpace(r.FormValue("amount"))
+	destInput := strings.TrimSpace(r.FormValue("destination"))
+	dateInput := strings.TrimSpace(r.FormValue("date"))
+	descriptionInput := strings.TrimSpace(r.FormValue("description"))
+
+	formProps := forms.CreateTransferProps{
+		SpaceID:         spaceID,
+		SourceAccountID: accountID,
+		DestAccounts:    dests,
+		Title:           titleInput,
+		Amount:          amountInput,
+		DestAccountID:   destInput,
+		Date:            dateInput,
+		Description:     descriptionInput,
+	}
+
+	hasErr := false
+	if titleInput == "" {
+		formProps.TitleErr = "Title is required."
+		hasErr = true
+	}
+
+	var amount decimal.Decimal
+	if amountInput == "" {
+		formProps.AmountErr = "Amount is required."
+		hasErr = true
+	} else {
+		amt, err := decimal.NewFromString(amountInput)
+		if err != nil {
+			formProps.AmountErr = "Enter a valid amount (e.g. 12.34)."
+			hasErr = true
+		} else if !amt.IsPositive() {
+			formProps.AmountErr = "Amount must be greater than zero."
+			hasErr = true
+		} else if amt.Exponent() < -2 {
+			formProps.AmountErr = "Amount can have at most 2 decimal places."
+			hasErr = true
+		} else {
+			amount = amt
+		}
+	}
+
+	if destInput == "" {
+		formProps.DestErr = "Choose a destination account."
+		hasErr = true
+	} else if destInput == accountID {
+		formProps.DestErr = "Destination must be a different account."
+		hasErr = true
+	} else {
+		// Verify the destination is in the same space (defends against hand-crafted requests).
+		destAcct, err := h.accountService.GetAccount(destInput)
+		if err != nil || destAcct.SpaceID != spaceID {
+			formProps.DestErr = "Destination account not found."
+			hasErr = true
+		}
+	}
+
+	var occurredAt time.Time
+	if dateInput == "" {
+		formProps.DateErr = "Date is required."
+		hasErr = true
+	} else {
+		parsed, err := time.Parse("2006-01-02", dateInput)
+		if err != nil {
+			formProps.DateErr = "Enter a valid date."
+			hasErr = true
+		} else {
+			occurredAt = parsed
+		}
+	}
+
+	if hasErr {
+		ui.Render(w, r, forms.CreateTransfer(formProps))
+		return
+	}
+
+	actorID := ""
+	if u := ctxkeys.User(r.Context()); u != nil {
+		actorID = u.ID
+	}
+
+	if _, err := h.transactionService.Transfer(service.TransferInput{
+		SourceAccountID: accountID,
+		DestAccountID:   destInput,
+		Title:           titleInput,
+		Amount:          amount,
+		OccurredAt:      occurredAt,
+		Description:     descriptionInput,
+		ActorID:         actorID,
+	}); err != nil {
+		slog.Error("failed to create transfer", "error", err, "source", accountID, "dest", destInput)
+		formProps.GeneralErr = "Something went wrong. Please try again."
+		ui.Render(w, r, forms.CreateTransfer(formProps))
+		return
+	}
+
+	redirectTo := routeurl.URL(
+		"page.app.spaces.space.accounts.account.overview",
+		"spaceID", spaceID,
+		"accountID", accountID,
+	)
+	w.Header().Set("HX-Redirect", redirectTo)
+	w.WriteHeader(http.StatusOK)
+}
+
+// transferDestinations returns every account in the space except the source.
+func (h *spaceHandler) transferDestinations(spaceID, sourceAccountID string) ([]*model.Account, error) {
+	all, err := h.accountService.GetAccountsForSpace(spaceID)
+	if err != nil {
+		return nil, err
+	}
+	out := make([]*model.Account, 0, len(all))
+	for _, a := range all {
+		if a.ID == sourceAccountID {
+			continue
+		}
+		out = append(out, a)
+	}
+	return out, nil
+}
+
 func (h *spaceHandler) HandleCreateBill(w http.ResponseWriter, r *http.Request) {
 	spaceID := r.PathValue("spaceID")
 	accountID := r.PathValue("accountID")

internal/repository/transaction.go

@@ -14,8 +14,11 @@ type TransactionRepository interface {
 	CreateDepositAtomic(t *model.Transaction, newBalance decimal.Decimal) error
 	UpdateBillAtomic(t *model.Transaction, newBalance decimal.Decimal, categoryID *string) error
 	UpdateDepositAtomic(t *model.Transaction, newBalance decimal.Decimal) error
+	TransferAtomic(withdrawal, deposit *model.Transaction, sourceNewBalance, destNewBalance decimal.Decimal) error
 	GetByID(id string) (*model.Transaction, error)
 	GetCategoryID(transactionID string) (*string, error)
+	GetRelatedID(transactionID string) (*string, error)
+	TransferIDsIn(ids []string) (map[string]bool, error)
 	ListByAccount(accountID string, limit, offset int) ([]*model.Transaction, error)
 	CountByAccount(accountID string) (int, error)
 }
@@ -138,6 +141,55 @@ func (r *transactionRepository) UpdateDepositAtomic(t *model.Transaction, newBal
 	})
 }
 
+// TransferAtomic creates the withdrawal + deposit transaction pair, updates both
+// account balances, and links the two via related_transactions in a single SQL
+// transaction. Negative balances are allowed — overdraft enforcement is a product
+// decision left to the service layer.
+func (r *transactionRepository) TransferAtomic(withdrawal, deposit *model.Transaction, sourceNewBalance, destNewBalance decimal.Decimal) error {
+	return WithTx(r.db, func(tx *sqlx.Tx) error {
+		insertTxn := `
+			INSERT INTO transactions
+				(id, value, type, account_id, title, description, occurred_at, created_at, updated_at)
+			VALUES ($1, $2, $3, $4, $5, $6, $7, $8, $9);
+		`
+		if _, err := tx.Exec(insertTxn,
+			withdrawal.ID, withdrawal.Value, withdrawal.Type, withdrawal.AccountID, withdrawal.Title,
+			withdrawal.Description, withdrawal.OccurredAt, withdrawal.CreatedAt, withdrawal.UpdatedAt,
+		); err != nil {
+			return err
+		}
+		if _, err := tx.Exec(insertTxn,
+			deposit.ID, deposit.Value, deposit.Type, deposit.AccountID, deposit.Title,
+			deposit.Description, deposit.OccurredAt, deposit.CreatedAt, deposit.UpdatedAt,
+		); err != nil {
+			return err
+		}
+
+		updateBalance := `UPDATE accounts SET balance = $1, updated_at = $2 WHERE id = $3;`
+		now := time.Now()
+		if _, err := tx.Exec(updateBalance, sourceNewBalance, now, withdrawal.AccountID); err != nil {
+			return err
+		}
+		if _, err := tx.Exec(updateBalance, destNewBalance, now, deposit.AccountID); err != nil {
+			return err
+		}
+
+		// related_transactions has CHECK (transaction_one_id < transaction_two_id);
+		// order the IDs to satisfy it.
+		one, two := withdrawal.ID, deposit.ID
+		if one > two {
+			one, two = two, one
+		}
+		if _, err := tx.Exec(
+			`INSERT INTO related_transactions (transaction_one_id, transaction_two_id) VALUES ($1, $2);`,
+			one, two,
+		); err != nil {
+			return err
+		}
+		return nil
+	})
+}
+
 func (r *transactionRepository) GetByID(id string) (*model.Transaction, error) {
 	query := `
 		SELECT id, value, type, account_id, title, description, occurred_at, created_at, updated_at
@@ -151,6 +203,55 @@ func (r *transactionRepository) GetByID(id string) (*model.Transaction, error) {
 	return t, nil
 }
 
+// GetRelatedID returns the other half of a transfer pair if `transactionID` is
+// part of one. Returns (nil, nil) when the transaction is standalone.
+func (r *transactionRepository) GetRelatedID(transactionID string) (*string, error) {
+	var other string
+	err := r.db.Get(&other, `
+		SELECT CASE
+			WHEN transaction_one_id = $1 THEN transaction_two_id
+			ELSE transaction_one_id
+		END
+		FROM related_transactions
+		WHERE transaction_one_id = $1 OR transaction_two_id = $1
+		LIMIT 1;
+	`, transactionID)
+	if err != nil {
+		if err == sql.ErrNoRows {
+			return nil, nil
+		}
+		return nil, err
+	}
+	return &other, nil
+}
+
+// TransferIDsIn returns the subset of `ids` that appear in related_transactions
+// (either side). Used by list pages to decide which rows are non-editable so we
+// don't N+1 a per-row check.
+func (r *transactionRepository) TransferIDsIn(ids []string) (map[string]bool, error) {
+	if len(ids) == 0 {
+		return map[string]bool{}, nil
+	}
+	query, args, err := sqlx.In(`
+		SELECT transaction_one_id AS id FROM related_transactions WHERE transaction_one_id IN (?)
+		UNION
+		SELECT transaction_two_id AS id FROM related_transactions WHERE transaction_two_id IN (?)
+	`, ids, ids)
+	if err != nil {
+		return nil, err
+	}
+	query = r.db.Rebind(query)
+	var hits []string
+	if err := r.db.Select(&hits, query, args...); err != nil {
+		return nil, err
+	}
+	out := make(map[string]bool, len(hits))
+	for _, id := range hits {
+		out[id] = true
+	}
+	return out, nil
+}
+
 func (r *transactionRepository) GetCategoryID(transactionID string) (*string, error) {
 	var id string
 	err := r.db.Get(&id, `SELECT category_id FROM transaction_categories WHERE transaction_id = $1 LIMIT 1;`, transactionID)

internal/repository/transaction_test.go

@@ -0,0 +1,113 @@
+package repository
+
+import (
+	"testing"
+	"time"
+
+	"git.juancwu.dev/juancwu/budgit/internal/model"
+	"git.juancwu.dev/juancwu/budgit/internal/testutil"
+	"github.com/google/uuid"
+	"github.com/shopspring/decimal"
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+func TestTransactionRepository_TransferAtomic_LinksPairAndUpdatesBalances(t *testing.T) {
+	testutil.ForEachDB(t, func(t *testing.T, dbi testutil.DBInfo) {
+		repo := NewTransactionRepository(dbi.DB)
+
+		user := testutil.CreateTestUser(t, dbi.DB, "transfer-repo@example.com", nil)
+		space := testutil.CreateTestSpace(t, dbi.DB, user.ID, "S")
+		src := testutil.CreateTestAccount(t, dbi.DB, space.ID, "Src")
+		dst := testutil.CreateTestAccount(t, dbi.DB, space.ID, "Dst")
+
+		now := time.Now()
+		withdrawal := &model.Transaction{
+			ID: uuid.NewString(), Value: decimal.NewFromInt(40), Type: model.TransactionTypeWithdrawal,
+			AccountID: src.ID, Title: "Move", OccurredAt: now, CreatedAt: now, UpdatedAt: now,
+		}
+		deposit := &model.Transaction{
+			ID: uuid.NewString(), Value: decimal.NewFromInt(40), Type: model.TransactionTypeDeposit,
+			AccountID: dst.ID, Title: "Move", OccurredAt: now, CreatedAt: now, UpdatedAt: now,
+		}
+
+		err := repo.TransferAtomic(withdrawal, deposit, decimal.NewFromInt(-40), decimal.NewFromInt(40))
+		require.NoError(t, err)
+
+		// Both transactions exist.
+		w, err := repo.GetByID(withdrawal.ID)
+		require.NoError(t, err)
+		assert.Equal(t, model.TransactionTypeWithdrawal, w.Type)
+		d, err := repo.GetByID(deposit.ID)
+		require.NoError(t, err)
+		assert.Equal(t, model.TransactionTypeDeposit, d.Type)
+
+		// Balances were applied.
+		accountRepo := NewAccountRepository(dbi.DB)
+		srcAfter, err := accountRepo.ByID(src.ID)
+		require.NoError(t, err)
+		assert.True(t, decimal.NewFromInt(-40).Equal(srcAfter.Balance))
+		dstAfter, err := accountRepo.ByID(dst.ID)
+		require.NoError(t, err)
+		assert.True(t, decimal.NewFromInt(40).Equal(dstAfter.Balance))
+
+		// Linked both ways via related_transactions.
+		other, err := repo.GetRelatedID(withdrawal.ID)
+		require.NoError(t, err)
+		require.NotNil(t, other)
+		assert.Equal(t, deposit.ID, *other)
+
+		other, err = repo.GetRelatedID(deposit.ID)
+		require.NoError(t, err)
+		require.NotNil(t, other)
+		assert.Equal(t, withdrawal.ID, *other)
+	})
+}
+
+func TestTransactionRepository_TransferIDsIn_ReturnsOnlyTransferHalves(t *testing.T) {
+	testutil.ForEachDB(t, func(t *testing.T, dbi testutil.DBInfo) {
+		repo := NewTransactionRepository(dbi.DB)
+
+		user := testutil.CreateTestUser(t, dbi.DB, "transferids@example.com", nil)
+		space := testutil.CreateTestSpace(t, dbi.DB, user.ID, "S")
+		src := testutil.CreateTestAccount(t, dbi.DB, space.ID, "Src")
+		dst := testutil.CreateTestAccount(t, dbi.DB, space.ID, "Dst")
+
+		// One transfer pair (source `w`, deposit `d`) plus one standalone txn.
+		now := time.Now()
+		w := &model.Transaction{ID: uuid.NewString(), Value: decimal.NewFromInt(5), Type: model.TransactionTypeWithdrawal, AccountID: src.ID, Title: "T-w", OccurredAt: now, CreatedAt: now, UpdatedAt: now}
+		d := &model.Transaction{ID: uuid.NewString(), Value: decimal.NewFromInt(5), Type: model.TransactionTypeDeposit, AccountID: dst.ID, Title: "T-d", OccurredAt: now, CreatedAt: now, UpdatedAt: now}
+		require.NoError(t, repo.TransferAtomic(w, d, decimal.NewFromInt(-5), decimal.NewFromInt(5)))
+		standalone := testutil.CreateTestTransaction(t, dbi.DB, src.ID, "solo", model.TransactionTypeDeposit, decimal.NewFromInt(1))
+
+		hits, err := repo.TransferIDsIn([]string{w.ID, d.ID, standalone.ID})
+		require.NoError(t, err)
+		assert.True(t, hits[w.ID], "withdrawal half should be flagged")
+		assert.True(t, hits[d.ID], "deposit half should be flagged")
+		assert.False(t, hits[standalone.ID], "standalone transaction should not be flagged")
+	})
+}
+
+func TestTransactionRepository_TransferIDsIn_EmptyInput(t *testing.T) {
+	testutil.ForEachDB(t, func(t *testing.T, dbi testutil.DBInfo) {
+		repo := NewTransactionRepository(dbi.DB)
+		hits, err := repo.TransferIDsIn(nil)
+		require.NoError(t, err)
+		assert.Empty(t, hits)
+	})
+}
+
+func TestTransactionRepository_GetRelatedID_NoneWhenStandalone(t *testing.T) {
+	testutil.ForEachDB(t, func(t *testing.T, dbi testutil.DBInfo) {
+		repo := NewTransactionRepository(dbi.DB)
+
+		user := testutil.CreateTestUser(t, dbi.DB, "standalone@example.com", nil)
+		space := testutil.CreateTestSpace(t, dbi.DB, user.ID, "S")
+		acct := testutil.CreateTestAccount(t, dbi.DB, space.ID, "A")
+		txn := testutil.CreateTestTransaction(t, dbi.DB, acct.ID, "x", model.TransactionTypeDeposit, decimal.NewFromInt(1))
+
+		other, err := repo.GetRelatedID(txn.ID)
+		require.NoError(t, err)
+		assert.Nil(t, other)
+	})
+}

internal/routes/routes.go

@@ -121,6 +121,8 @@ func SetupRoutes(a *app.App) http.Handler {
 					g.Post("/bills/create", spaceH.HandleCreateBill).Name("action.app.spaces.space.accounts.account.bills.create")
 					g.Get("/deposits/create", spaceH.SpaceCreateDepositPage).Name("page.app.spaces.space.accounts.account.deposits.create")
 					g.Post("/deposits/create", spaceH.HandleCreateDeposit).Name("action.app.spaces.space.accounts.account.deposits.create")
+					g.Get("/transfers/create", spaceH.SpaceCreateTransferPage).Name("page.app.spaces.space.accounts.account.transfers.create")
+					g.Post("/transfers/create", spaceH.HandleCreateTransfer).Name("action.app.spaces.space.accounts.account.transfers.create")
 				})
 			})
 		})

internal/service/transaction.go

@@ -1,6 +1,7 @@
 package service
 
 import (
+	"errors"
 	"fmt"
 	"strings"
 	"time"
@@ -11,6 +12,13 @@ import (
 	"github.com/shopspring/decimal"
 )
 
+// ErrTransactionPartOfTransfer is returned when an operation that mutates a
+// single transaction (edit, delete) is attempted on one half of a transfer.
+// Transfers must be edited as a pair or not at all to keep both sides in sync;
+// callers should surface a user-facing message and offer to undo the transfer
+// instead.
+var ErrTransactionPartOfTransfer = errors.New("transaction is part of a transfer")
+
 type TransactionService struct {
 	transactionRepo repository.TransactionRepository
 	categoryRepo    repository.CategoryRepository
@@ -176,6 +184,153 @@ func (s *TransactionService) Deposit(input DepositInput) (*model.Transaction, er
 	return txn, nil
 }
 
+type TransferInput struct {
+	SourceAccountID string
+	DestAccountID   string
+	Title           string
+	Amount          decimal.Decimal
+	OccurredAt      time.Time
+	Description     string
+	ActorID         string
+}
+
+// TransferResult is what the service returns after a successful transfer — both
+// halves are surfaced so callers can audit, redirect, or render either side.
+type TransferResult struct {
+	Withdrawal *model.Transaction
+	Deposit    *model.Transaction
+}
+
+// Transfer moves funds from one account to another. It creates two linked
+// transactions (a withdrawal on the source, a deposit on the destination) plus
+// a row in related_transactions, all in a single SQL transaction.
+//
+// Negative balances are intentionally allowed — the product permits overdraft.
+// Source must differ from destination; the amount must be positive (the sign is
+// implicit in the transaction type).
+func (s *TransactionService) Transfer(input TransferInput) (*TransferResult, error) {
+	title := strings.TrimSpace(input.Title)
+	if title == "" {
+		return nil, fmt.Errorf("title is required")
+	}
+	if input.SourceAccountID == "" || input.DestAccountID == "" {
+		return nil, fmt.Errorf("source and destination account ids are required")
+	}
+	if input.SourceAccountID == input.DestAccountID {
+		return nil, fmt.Errorf("source and destination must differ")
+	}
+	if !input.Amount.IsPositive() {
+		return nil, fmt.Errorf("amount must be greater than zero")
+	}
+	if input.OccurredAt.IsZero() {
+		return nil, fmt.Errorf("date is required")
+	}
+
+	source, err := s.accountService.GetAccount(input.SourceAccountID)
+	if err != nil {
+		return nil, fmt.Errorf("failed to load source account: %w", err)
+	}
+	dest, err := s.accountService.GetAccount(input.DestAccountID)
+	if err != nil {
+		return nil, fmt.Errorf("failed to load destination account: %w", err)
+	}
+
+	now := time.Now()
+	var description *string
+	if d := strings.TrimSpace(input.Description); d != "" {
+		description = &d
+	}
+
+	withdrawal := &model.Transaction{
+		ID:          uuid.NewString(),
+		Value:       input.Amount,
+		Type:        model.TransactionTypeWithdrawal,
+		AccountID:   source.ID,
+		Title:       title,
+		Description: description,
+		OccurredAt:  input.OccurredAt,
+		CreatedAt:   now,
+		UpdatedAt:   now,
+	}
+	deposit := &model.Transaction{
+		ID:          uuid.NewString(),
+		Value:       input.Amount,
+		Type:        model.TransactionTypeDeposit,
+		AccountID:   dest.ID,
+		Title:       title,
+		Description: description,
+		OccurredAt:  input.OccurredAt,
+		CreatedAt:   now,
+		UpdatedAt:   now,
+	}
+
+	sourceNewBalance := source.Balance.Sub(input.Amount)
+	destNewBalance := dest.Balance.Add(input.Amount)
+
+	if err := s.transactionRepo.TransferAtomic(withdrawal, deposit, sourceNewBalance, destNewBalance); err != nil {
+		return nil, fmt.Errorf("failed to record transfer: %w", err)
+	}
+
+	// Audit each side. Metadata captures the role and the other half so the
+	// activity feed can render "Transferred to/from <other account>" without a
+	// follow-up query.
+	s.auditSvc.Record(TransactionRecordOptions{
+		TransactionID: withdrawal.ID,
+		ActorID:       input.ActorID,
+		Action:        model.TransactionAuditActionCreated,
+		Metadata: map[string]any{
+			"account_id":          withdrawal.AccountID,
+			"transaction_type":    string(withdrawal.Type),
+			"title":               withdrawal.Title,
+			"amount":              withdrawal.Value.StringFixedBank(2),
+			"transfer_role":       "source",
+			"transfer_pair_id":    deposit.ID,
+			"transfer_other_acct": deposit.AccountID,
+			"transfer_other_name": dest.Name,
+		},
+	})
+	s.auditSvc.Record(TransactionRecordOptions{
+		TransactionID: deposit.ID,
+		ActorID:       input.ActorID,
+		Action:        model.TransactionAuditActionCreated,
+		Metadata: map[string]any{
+			"account_id":          deposit.AccountID,
+			"transaction_type":    string(deposit.Type),
+			"title":               deposit.Title,
+			"amount":              deposit.Value.StringFixedBank(2),
+			"transfer_role":       "destination",
+			"transfer_pair_id":    withdrawal.ID,
+			"transfer_other_acct": withdrawal.AccountID,
+			"transfer_other_name": source.Name,
+		},
+	})
+
+	return &TransferResult{Withdrawal: withdrawal, Deposit: deposit}, nil
+}
+
+// TransferIDsIn returns the subset of the given transaction IDs that are part
+// of a transfer pair. Empty input yields an empty (non-nil) map.
+func (s *TransactionService) TransferIDsIn(ids []string) (map[string]bool, error) {
+	hits, err := s.transactionRepo.TransferIDsIn(ids)
+	if err != nil {
+		return nil, fmt.Errorf("failed to look up transfer ids: %w", err)
+	}
+	return hits, nil
+}
+
+// GetRelatedTransactionID returns the other half of a transfer pair, or "" if
+// the transaction is not part of a transfer.
+func (s *TransactionService) GetRelatedTransactionID(transactionID string) (string, error) {
+	id, err := s.transactionRepo.GetRelatedID(transactionID)
+	if err != nil {
+		return "", fmt.Errorf("failed to load related transaction: %w", err)
+	}
+	if id == nil {
+		return "", nil
+	}
+	return *id, nil
+}
+
 type UpdateBillInput struct {
 	TransactionID string
 	Title         string
@@ -208,6 +363,11 @@ func (s *TransactionService) UpdateBill(input UpdateBillInput) (*model.Transacti
 	if existing.Type != model.TransactionTypeWithdrawal {
 		return nil, fmt.Errorf("transaction is not a bill")
 	}
+	if related, err := s.transactionRepo.GetRelatedID(existing.ID); err != nil {
+		return nil, fmt.Errorf("failed to check transfer linkage: %w", err)
+	} else if related != nil {
+		return nil, ErrTransactionPartOfTransfer
+	}
 
 	account, err := s.accountService.GetAccount(existing.AccountID)
 	if err != nil {
@@ -289,6 +449,11 @@ func (s *TransactionService) UpdateDeposit(input UpdateDepositInput) (*model.Tra
 	if existing.Type != model.TransactionTypeDeposit {
 		return nil, fmt.Errorf("transaction is not a deposit")
 	}
+	if related, err := s.transactionRepo.GetRelatedID(existing.ID); err != nil {
+		return nil, fmt.Errorf("failed to check transfer linkage: %w", err)
+	} else if related != nil {
+		return nil, ErrTransactionPartOfTransfer
+	}
 
 	account, err := s.accountService.GetAccount(existing.AccountID)
 	if err != nil {

internal/service/transaction_test.go

@@ -246,6 +246,241 @@ func TestTransactionService_UpdateDeposit_RejectsBillTransaction(t *testing.T) {
 	})
 }
 
+func TestTransactionService_Transfer_HappyPath(t *testing.T) {
+	testutil.ForEachDB(t, func(t *testing.T, dbi testutil.DBInfo) {
+		f := newTxnFixture(t, dbi)
+		dest := testutil.CreateTestAccount(t, dbi.DB, f.account.SpaceID, "Savings")
+
+		result, err := f.svc.Transfer(TransferInput{
+			SourceAccountID: f.account.ID,
+			DestAccountID:   dest.ID,
+			Title:           "Move to savings",
+			Amount:          decimal.NewFromInt(50),
+			OccurredAt:      time.Now(),
+			ActorID:         f.user.ID,
+		})
+		require.NoError(t, err)
+		require.NotNil(t, result.Withdrawal)
+		require.NotNil(t, result.Deposit)
+		assert.Equal(t, model.TransactionTypeWithdrawal, result.Withdrawal.Type)
+		assert.Equal(t, model.TransactionTypeDeposit, result.Deposit.Type)
+		assert.Equal(t, f.account.ID, result.Withdrawal.AccountID)
+		assert.Equal(t, dest.ID, result.Deposit.AccountID)
+
+		// Source went from 0 → -50 (overdraft allowed); dest 0 → +50.
+		src, err := f.accounts.ByID(f.account.ID)
+		require.NoError(t, err)
+		assert.True(t, decimal.NewFromInt(-50).Equal(src.Balance))
+		dst, err := f.accounts.ByID(dest.ID)
+		require.NoError(t, err)
+		assert.True(t, decimal.NewFromInt(50).Equal(dst.Balance))
+
+		// Transactions are linked.
+		relatedID, err := f.svc.GetRelatedTransactionID(result.Withdrawal.ID)
+		require.NoError(t, err)
+		assert.Equal(t, result.Deposit.ID, relatedID)
+
+		// Audit recorded both sides with the right transfer_role and other-account name.
+		wlogs, err := f.txAudit.ListByTransaction(result.Withdrawal.ID, 10, 0)
+		require.NoError(t, err)
+		require.Len(t, wlogs, 1)
+		var wmeta map[string]any
+		require.NoError(t, json.Unmarshal(wlogs[0].Metadata, &wmeta))
+		assert.Equal(t, "source", wmeta["transfer_role"])
+		assert.Equal(t, result.Deposit.ID, wmeta["transfer_pair_id"])
+		assert.Equal(t, "Savings", wmeta["transfer_other_name"])
+
+		dlogs, err := f.txAudit.ListByTransaction(result.Deposit.ID, 10, 0)
+		require.NoError(t, err)
+		require.Len(t, dlogs, 1)
+		var dmeta map[string]any
+		require.NoError(t, json.Unmarshal(dlogs[0].Metadata, &dmeta))
+		assert.Equal(t, "destination", dmeta["transfer_role"])
+		assert.Equal(t, result.Withdrawal.ID, dmeta["transfer_pair_id"])
+		assert.Equal(t, "Acct", dmeta["transfer_other_name"])
+	})
+}
+
+func TestTransactionService_Transfer_AllowsOverdraft(t *testing.T) {
+	testutil.ForEachDB(t, func(t *testing.T, dbi testutil.DBInfo) {
+		f := newTxnFixture(t, dbi)
+		dest := testutil.CreateTestAccount(t, dbi.DB, f.account.SpaceID, "B")
+
+		// Seed source to 100, then transfer 200 → -100.
+		_, err := f.svc.Deposit(DepositInput{
+			AccountID: f.account.ID, Title: "seed", Amount: decimal.NewFromInt(100),
+			OccurredAt: time.Now(), ActorID: f.user.ID,
+		})
+		require.NoError(t, err)
+		_, err = f.svc.Transfer(TransferInput{
+			SourceAccountID: f.account.ID, DestAccountID: dest.ID,
+			Title: "T1", Amount: decimal.NewFromInt(200), OccurredAt: time.Now(), ActorID: f.user.ID,
+		})
+		require.NoError(t, err)
+
+		src, err := f.accounts.ByID(f.account.ID)
+		require.NoError(t, err)
+		assert.True(t, decimal.NewFromInt(-100).Equal(src.Balance), "expected -100, got %s", src.Balance.String())
+
+		// Transfer another 200 from -100 → -300.
+		_, err = f.svc.Transfer(TransferInput{
+			SourceAccountID: f.account.ID, DestAccountID: dest.ID,
+			Title: "T2", Amount: decimal.NewFromInt(200), OccurredAt: time.Now(), ActorID: f.user.ID,
+		})
+		require.NoError(t, err)
+
+		src, err = f.accounts.ByID(f.account.ID)
+		require.NoError(t, err)
+		assert.True(t, decimal.NewFromInt(-300).Equal(src.Balance), "expected -300, got %s", src.Balance.String())
+	})
+}
+
+// TestTransactionService_Transfer_AppearsInAccountActivityFeeds is the regression
+// test for "make sure activity logs are also created". The activity views on each
+// account page and the space-level page merge transaction_audit_logs into a unified
+// feed; this test exercises the full path end-to-end so silent gaps in audit
+// recording or merging would fail.
+func TestTransactionService_Transfer_AppearsInActivityFeeds(t *testing.T) {
+	testutil.ForEachDB(t, func(t *testing.T, dbi testutil.DBInfo) {
+		f := newTxnFixture(t, dbi)
+		dest := testutil.CreateTestAccount(t, dbi.DB, f.account.SpaceID, "Savings")
+
+		spaceAuditRepo := repository.NewSpaceAuditLogRepository(dbi.DB)
+		activitySvc := NewAccountActivityService(
+			NewSpaceAuditLogService(spaceAuditRepo),
+			NewTransactionAuditLogService(f.txAudit),
+		)
+
+		result, err := f.svc.Transfer(TransferInput{
+			SourceAccountID: f.account.ID,
+			DestAccountID:   dest.ID,
+			Title:           "Move to savings",
+			Amount:          decimal.NewFromInt(75),
+			OccurredAt:      time.Now(),
+			ActorID:         f.user.ID,
+		})
+		require.NoError(t, err)
+
+		// Source account activity sees the withdrawal half.
+		srcRows, err := activitySvc.List(f.account.ID, 10, 0)
+		require.NoError(t, err)
+		require.Len(t, srcRows, 1, "source account feed should include the withdrawal half")
+		require.NotNil(t, srcRows[0].TxLog)
+		assert.Equal(t, result.Withdrawal.ID, srcRows[0].TxLog.TransactionID)
+		assertTransferRole(t, srcRows[0].TxLog, "source", dest.ID)
+
+		// Destination account activity sees the deposit half.
+		dstRows, err := activitySvc.List(dest.ID, 10, 0)
+		require.NoError(t, err)
+		require.Len(t, dstRows, 1, "destination account feed should include the deposit half")
+		require.NotNil(t, dstRows[0].TxLog)
+		assert.Equal(t, result.Deposit.ID, dstRows[0].TxLog.TransactionID)
+		assertTransferRole(t, dstRows[0].TxLog, "destination", f.account.ID)
+
+		// Space-level activity feed sees both halves.
+		spaceRows, err := activitySvc.ListSpace(f.account.SpaceID, 10, 0)
+		require.NoError(t, err)
+		require.Len(t, spaceRows, 2, "space feed should include both halves of the transfer")
+		ids := []string{}
+		for _, r := range spaceRows {
+			require.NotNil(t, r.TxLog)
+			ids = append(ids, r.TxLog.TransactionID)
+		}
+		assert.Contains(t, ids, result.Withdrawal.ID)
+		assert.Contains(t, ids, result.Deposit.ID)
+
+		// Counts agree with what the feed returns (pagination relies on this).
+		srcCount, err := activitySvc.Count(f.account.ID)
+		require.NoError(t, err)
+		assert.Equal(t, 1, srcCount)
+		dstCount, err := activitySvc.Count(dest.ID)
+		require.NoError(t, err)
+		assert.Equal(t, 1, dstCount)
+		spaceCount, err := activitySvc.CountSpace(f.account.SpaceID)
+		require.NoError(t, err)
+		// Source account had no activity before the transfer, dest is brand-new;
+		// the only activity in the space is the two transfer halves.
+		assert.Equal(t, 2, spaceCount)
+	})
+}
+
+func assertTransferRole(t *testing.T, log *model.TransactionAuditLogWithActor, expectedRole, expectedOtherAcctID string) {
+	t.Helper()
+	var meta map[string]any
+	require.NoError(t, json.Unmarshal(log.Metadata, &meta))
+	assert.Equal(t, expectedRole, meta["transfer_role"])
+	assert.Equal(t, expectedOtherAcctID, meta["transfer_other_acct"])
+}
+
+func TestTransactionService_Transfer_RejectsSameAccount(t *testing.T) {
+	testutil.ForEachDB(t, func(t *testing.T, dbi testutil.DBInfo) {
+		f := newTxnFixture(t, dbi)
+		_, err := f.svc.Transfer(TransferInput{
+			SourceAccountID: f.account.ID,
+			DestAccountID:   f.account.ID,
+			Title:           "Self",
+			Amount:          decimal.NewFromInt(10),
+			OccurredAt:      time.Now(),
+			ActorID:         f.user.ID,
+		})
+		assert.Error(t, err)
+	})
+}
+
+func TestTransactionService_Transfer_RejectsNonPositiveAmount(t *testing.T) {
+	testutil.ForEachDB(t, func(t *testing.T, dbi testutil.DBInfo) {
+		f := newTxnFixture(t, dbi)
+		dest := testutil.CreateTestAccount(t, dbi.DB, f.account.SpaceID, "B")
+		_, err := f.svc.Transfer(TransferInput{
+			SourceAccountID: f.account.ID, DestAccountID: dest.ID,
+			Title: "x", Amount: decimal.NewFromInt(0), OccurredAt: time.Now(), ActorID: f.user.ID,
+		})
+		assert.Error(t, err)
+	})
+}
+
+func TestTransactionService_Update_RejectsTransferTransactions(t *testing.T) {
+	testutil.ForEachDB(t, func(t *testing.T, dbi testutil.DBInfo) {
+		f := newTxnFixture(t, dbi)
+		dest := testutil.CreateTestAccount(t, dbi.DB, f.account.SpaceID, "Savings")
+
+		result, err := f.svc.Transfer(TransferInput{
+			SourceAccountID: f.account.ID,
+			DestAccountID:   dest.ID,
+			Title:           "Initial",
+			Amount:          decimal.NewFromInt(20),
+			OccurredAt:      time.Now(),
+			ActorID:         f.user.ID,
+		})
+		require.NoError(t, err)
+
+		// The withdrawal half cannot be edited via UpdateBill.
+		_, err = f.svc.UpdateBill(UpdateBillInput{
+			TransactionID: result.Withdrawal.ID,
+			Title:         "tampered",
+			Amount:        decimal.NewFromInt(99),
+			OccurredAt:    time.Now(),
+			ActorID:       f.user.ID,
+		})
+		require.ErrorIs(t, err, ErrTransactionPartOfTransfer)
+
+		// The deposit half cannot be edited via UpdateDeposit.
+		_, err = f.svc.UpdateDeposit(UpdateDepositInput{
+			TransactionID: result.Deposit.ID,
+			Title:         "tampered",
+			Amount:        decimal.NewFromInt(99),
+			OccurredAt:    time.Now(),
+			ActorID:       f.user.ID,
+		})
+		require.ErrorIs(t, err, ErrTransactionPartOfTransfer)
+
+		// Underlying transaction is untouched (no audit `edited` row added either).
+		count, err := f.txAudit.CountByTransaction(result.Withdrawal.ID)
+		require.NoError(t, err)
+		assert.Equal(t, 1, count, "only the original `created` audit row should exist")
+	})
+}
+
 func TestTransactionService_Validations(t *testing.T) {
 	testutil.ForEachDB(t, func(t *testing.T, dbi testutil.DBInfo) {
 		f := newTxnFixture(t, dbi)

internal/ui/blocks/transaction_list.templ

@@ -10,6 +10,9 @@ type TransactionListProps struct {
 	SpaceID      string
 	AccountID    string
 	Transactions []*model.Transaction
+	// NonEditableIDs marks transaction IDs whose Edit button should be hidden
+	// (currently: transfer halves). Nil/empty means everything is editable.
+	NonEditableIDs map[string]bool
 }
 
 templ TransactionList(props TransactionListProps) {
@@ -20,13 +23,13 @@ templ TransactionList(props TransactionListProps) {
 	} else {
 		<ul class="divide-y">
 			for _, t := range props.Transactions {
-				@transactionRow(props.SpaceID, props.AccountID, t)
+				@transactionRow(props.SpaceID, props.AccountID, t, !props.NonEditableIDs[t.ID])
 			}
 		</ul>
 	}
 }
 
-templ transactionRow(spaceID, accountID string, t *model.Transaction) {
+templ transactionRow(spaceID, accountID string, t *model.Transaction, editable bool) {
 	{{
 		isDeposit := t.Type == model.TransactionTypeDeposit
 		amountClasses := []string{"text-sm font-semibold tabular-nums"}
@@ -70,7 +73,7 @@ templ transactionRow(spaceID, accountID string, t *model.Transaction) {
 					<p class="text-xs text-muted-foreground truncate max-w-[200px]">{ *t.Description }</p>
 				}
 			</div>
-			if spaceID != "" && accountID != "" {
+			if spaceID != "" && accountID != "" && editable {
 				@button.Button(button.Props{
 					Variant: button.VariantGhost,
 					Size:    button.SizeIcon,

internal/ui/forms/create_transfer.templ

@@ -0,0 +1,176 @@
+package forms
+
+import "git.juancwu.dev/juancwu/budgit/internal/model"
+import "git.juancwu.dev/juancwu/budgit/internal/routeurl"
+import "git.juancwu.dev/juancwu/budgit/internal/ui/components/button"
+import "git.juancwu.dev/juancwu/budgit/internal/ui/components/card"
+import "git.juancwu.dev/juancwu/budgit/internal/ui/components/form"
+import "git.juancwu.dev/juancwu/budgit/internal/ui/components/input"
+import "git.juancwu.dev/juancwu/budgit/internal/ui/components/textarea"
+
+type CreateTransferProps struct {
+	SpaceID         string
+	SourceAccountID string
+
+	// DestAccounts is the list of other accounts in the same space the user
+	// can transfer to. Excludes the source account.
+	DestAccounts []*model.Account
+
+	Title         string
+	Amount        string
+	DestAccountID string
+	Date          string
+	Description   string
+
+	TitleErr   string
+	AmountErr  string
+	DestErr    string
+	DateErr    string
+	GeneralErr string
+}
+
+templ CreateTransfer(props CreateTransferProps) {
+	<form hx-post={ routeurl.URL("action.app.spaces.space.accounts.account.transfers.create", "spaceID", props.SpaceID, "accountID", props.SourceAccountID) }>
+		@card.Card(card.Props{Class: "rounded-sm"}) {
+			@card.Content(card.ContentProps{Class: "p-4 space-y-4"}) {
+				if props.GeneralErr != "" {
+					@form.Message(form.MessageProps{Variant: form.MessageVariantError}) {
+						{ props.GeneralErr }
+					}
+				}
+				@form.Item() {
+					@form.Label(form.LabelProps{For: "title"}) {
+						Title
+					}
+					@input.Input(input.Props{
+						ID:          "title",
+						Name:        "title",
+						Type:        input.TypeText,
+						Placeholder: "e.g. Move to savings",
+						Class:       "rounded-sm",
+						Value:       props.Title,
+						HasError:    props.TitleErr != "",
+						Required:    true,
+						Attributes: templ.Attributes{
+							"autocomplete": "off",
+							"autofocus":    "",
+						},
+					})
+					if props.TitleErr != "" {
+						@form.Message(form.MessageProps{Variant: form.MessageVariantError}) {
+							{ props.TitleErr }
+						}
+					}
+				}
+				@form.Item() {
+					@form.Label(form.LabelProps{For: "destination"}) {
+						Destination account
+					}
+					if len(props.DestAccounts) == 0 {
+						@form.Message(form.MessageProps{Variant: form.MessageVariantError}) {
+							This space has no other accounts. Create one first.
+						}
+					} else {
+						<select
+							id="destination"
+							name="destination"
+							class={ "flex h-9 w-full items-center rounded-sm border bg-transparent px-3 py-1 text-sm shadow-sm focus-visible:outline-none focus-visible:ring-1 focus-visible:ring-ring",
+								templ.KV("border-destructive", props.DestErr != ""),
+								templ.KV("border-input", props.DestErr == "") }
+							required
+						>
+							<option value="" selected?={ props.DestAccountID == "" }>Select an account…</option>
+							for _, a := range props.DestAccounts {
+								<option value={ a.ID } selected?={ props.DestAccountID == a.ID }>{ a.Name }</option>
+							}
+						</select>
+					}
+					if props.DestErr != "" {
+						@form.Message(form.MessageProps{Variant: form.MessageVariantError}) {
+							{ props.DestErr }
+						}
+					}
+				}
+				<div class="grid grid-cols-1 md:grid-cols-2 gap-4">
+					@form.Item() {
+						@form.Label(form.LabelProps{For: "amount"}) {
+							Amount
+						}
+						@input.Input(input.Props{
+							ID:          "amount",
+							Name:        "amount",
+							Type:        input.TypeNumber,
+							Placeholder: "0.00",
+							Class:       "rounded-sm",
+							Value:       props.Amount,
+							HasError:    props.AmountErr != "",
+							Required:    true,
+							Attributes: templ.Attributes{
+								"step":         "0.01",
+								"min":          "0",
+								"inputmode":    "decimal",
+								"autocomplete": "off",
+							},
+						})
+						if props.AmountErr != "" {
+							@form.Message(form.MessageProps{Variant: form.MessageVariantError}) {
+								{ props.AmountErr }
+							}
+						}
+						@form.Description() {
+							Transfers may exceed the source balance and result in a negative balance.
+						}
+					}
+					@form.Item() {
+						@form.Label(form.LabelProps{For: "date"}) {
+							Date
+						}
+						@input.Input(input.Props{
+							ID:       "date",
+							Name:     "date",
+							Type:     input.TypeDate,
+							Class:    "rounded-sm",
+							Value:    props.Date,
+							HasError: props.DateErr != "",
+							Required: true,
+						})
+						if props.DateErr != "" {
+							@form.Message(form.MessageProps{Variant: form.MessageVariantError}) {
+								{ props.DateErr }
+							}
+						}
+					}
+				</div>
+				@form.Item() {
+					@form.Label(form.LabelProps{For: "description"}) {
+						Description
+					}
+					@textarea.Textarea(textarea.Props{
+						ID:          "description",
+						Name:        "description",
+						Placeholder: "Anything extra worth remembering",
+						Rows:        3,
+						Value:       props.Description,
+					})
+					@form.Description() {
+						Optional. Shared by both sides of the transfer.
+					}
+				}
+			}
+			@card.Footer(card.FooterProps{Class: "flex justify-end gap-2"}) {
+				@button.Button(button.Props{
+					Variant: button.VariantGhost,
+					Href:    routeurl.URL("page.app.spaces.space.accounts.account.overview", "spaceID", props.SpaceID, "accountID", props.SourceAccountID),
+				}) {
+					Cancel
+				}
+				@button.Button(button.Props{
+					Type:     button.TypeSubmit,
+					Disabled: len(props.DestAccounts) == 0,
+				}) {
+					Transfer
+				}
+			}
+		}
+	</form>
+}

internal/ui/pages/space_account.templ

@@ -16,7 +16,8 @@ type SpaceAccountPageProps struct {
 	AccountID          string
 	AccountName        string
 	AccountBalance     decimal.Decimal
-	RecentTransactions []*model.Transaction
+	RecentTransactions       []*model.Transaction
+	NonEditableTransactionIDs map[string]bool
 }
 
 templ SpaceAccountPage(props SpaceAccountPageProps) {
@@ -92,9 +93,10 @@ templ SpaceAccountPage(props SpaceAccountPageProps) {
 					}
 					@card.Content() {
 						@blocks.TransactionList(blocks.TransactionListProps{
-							SpaceID:      props.SpaceID,
-							AccountID:    props.AccountID,
-							Transactions: props.RecentTransactions,
+							SpaceID:        props.SpaceID,
+							AccountID:      props.AccountID,
+							Transactions:   props.RecentTransactions,
+							NonEditableIDs: props.NonEditableTransactionIDs,
 						})
 					}
 					@card.Footer(card.FooterProps{Class: "justify-end"}) {

internal/ui/pages/space_account_activity.templ

@@ -147,9 +147,12 @@ func accountActivityTxMessage(spaceID, accountID string, log *model.TransactionA
 	switch log.Action {
 	case model.TransactionAuditActionCreated:
 		var meta struct {
-			TransactionType string `json:"transaction_type"`
-			Title           string `json:"title"`
-			Amount          string `json:"amount"`
+			TransactionType   string `json:"transaction_type"`
+			Title             string `json:"title"`
+			Amount            string `json:"amount"`
+			TransferRole      string `json:"transfer_role"`
+			TransferOtherAcct string `json:"transfer_other_acct"`
+			TransferOtherName string `json:"transfer_other_name"`
 		}
 		_ = json.Unmarshal(log.Metadata, &meta)
 		title := meta.Title
@@ -161,6 +164,20 @@ func accountActivityTxMessage(spaceID, accountID string, log *model.TransactionA
 		if meta.Amount != "" {
 			amountSuffix = fmt.Sprintf(" for $%s", templEscape(meta.Amount))
 		}
+		// Transfer events get a more descriptive sentence so users can see
+		// which side this entry is and where the money went / came from.
+		if meta.TransferRole != "" {
+			direction := "to"
+			if meta.TransferRole == "destination" {
+				direction = "from"
+			}
+			otherName := meta.TransferOtherName
+			if otherName == "" {
+				otherName = "another account"
+			}
+			return fmt.Sprintf("%s transferred %s%s %s %s.",
+				actor, titleHTML, amountSuffix, templEscape(direction), bold(otherName))
+		}
 		return fmt.Sprintf("%s added a %s %s%s.",
 			actor, templEscape(transactionTypeLabel(meta.TransactionType)), titleHTML, amountSuffix)
 	case model.TransactionAuditActionEdited:

internal/ui/pages/space_account_transactions.templ

@@ -11,15 +11,16 @@ import "git.juancwu.dev/juancwu/budgit/internal/ui/components/icon"
 import "git.juancwu.dev/juancwu/budgit/internal/ui/components/pagination"
 
 type SpaceAccountTransactionsPageProps struct {
-	SpaceID      string
-	SpaceName    string
-	AccountID    string
-	AccountName  string
-	Transactions []*model.Transaction
-	CurrentPage  int
-	TotalPages   int
-	TotalCount   int
-	PerPage      int
+	SpaceID                  string
+	SpaceName                string
+	AccountID                string
+	AccountName              string
+	Transactions             []*model.Transaction
+	NonEditableTransactionIDs map[string]bool
+	CurrentPage              int
+	TotalPages               int
+	TotalCount               int
+	PerPage                  int
 }
 
 templ SpaceAccountTransactionsPage(props SpaceAccountTransactionsPageProps) {
@@ -62,9 +63,10 @@ templ SpaceAccountTransactionsPage(props SpaceAccountTransactionsPageProps) {
 				}
 				@card.Content() {
 					@blocks.TransactionList(blocks.TransactionListProps{
-						SpaceID:      props.SpaceID,
-						AccountID:    props.AccountID,
-						Transactions: props.Transactions,
+						SpaceID:        props.SpaceID,
+						AccountID:      props.AccountID,
+						Transactions:   props.Transactions,
+						NonEditableIDs: props.NonEditableTransactionIDs,
 					})
 				}
 				if props.TotalPages > 1 {

internal/ui/pages/space_create_transfer.templ

@@ -0,0 +1,32 @@
+package pages
+
+import "git.juancwu.dev/juancwu/budgit/internal/ui/forms"
+import "git.juancwu.dev/juancwu/budgit/internal/ui/layouts"
+
+type SpaceCreateTransferPageProps struct {
+	SpaceID     string
+	SpaceName   string
+	AccountID   string
+	AccountName string
+	Form        forms.CreateTransferProps
+}
+
+templ SpaceCreateTransferPage(props SpaceCreateTransferPageProps) {
+	@layouts.AppWithBreadcrumb(
+		"Transfer Funds",
+		accountChildBreadcrumb(props.SpaceID, props.SpaceName, props.AccountID, props.AccountName, "Transfer Funds"),
+		spaceOverviewSidebarContent(),
+		spaceSpecificSidebarContent(props.SpaceID),
+		spaceAccountSidebarContent(props.SpaceID, props.AccountID),
+	) {
+		<div class="container max-w-3xl px-6 py-8 mx-auto space-y-8">
+			<div>
+				<h1 class="text-3xl font-bold">Transfer Funds</h1>
+				<p class="text-muted-foreground mt-2">
+					Move money out of { props.AccountName } into another account in this space.
+				</p>
+			</div>
+			@forms.CreateTransfer(props.Form)
+		</div>
+	}
+}

internal/ui/pages/space_overview.templ

@@ -144,6 +144,16 @@ templ spaceAccountSidebarContent(spaceID, accountID string) {
 					<span>Deposit Funds</span>
 				}
 			}
+			@sidebar.MenuItem() {
+				@sidebar.MenuButton(sidebar.MenuButtonProps{
+					Href:     routeurl.URL("page.app.spaces.space.accounts.account.transfers.create", "spaceID", spaceID, "accountID", accountID),
+					IsActive: ctxkeys.URLPath(ctx) == routeurl.URL("page.app.spaces.space.accounts.account.transfers.create", "spaceID", spaceID, "accountID", accountID),
+					Tooltip:  "Transfer Funds",
+				}) {
+					@icon.ArrowRightLeft()
+					<span>Transfer Funds</span>
+				}
+			}
 			@sidebar.MenuItem() {
 				@sidebar.MenuButton(sidebar.MenuButtonProps{
 					Href:     routeurl.URL("page.app.spaces.space.accounts.account.activity", "spaceID", spaceID, "accountID", accountID),

internal/ui/pages/space_transaction.templ

@@ -9,14 +9,16 @@ import "git.juancwu.dev/juancwu/budgit/internal/ui/layouts"
 import "git.juancwu.dev/juancwu/budgit/internal/ui/utils"
 
 type SpaceTransactionPageProps struct {
-	SpaceID         string
-	SpaceName       string
-	AccountID       string
-	AccountName     string
-	Transaction     *model.Transaction
-	CategoryName    string
-	RecentAuditLogs []*model.TransactionAuditLogWithActor
-	AuditLogCount   int
+	SpaceID            string
+	SpaceName          string
+	AccountID          string
+	AccountName        string
+	Transaction        *model.Transaction
+	CategoryName       string
+	RecentAuditLogs    []*model.TransactionAuditLogWithActor
+	AuditLogCount      int
+	RelatedTransaction *model.Transaction
+	RelatedAccount     *model.Account
 }
 
 templ SpaceTransactionPage(props SpaceTransactionPageProps) {
@@ -53,13 +55,15 @@ templ SpaceTransactionPage(props SpaceTransactionPageProps) {
 						{ label } in { props.AccountName }
 					</p>
 				</div>
-				@button.Button(button.Props{
-					Variant: button.VariantDefault,
-					Href:    routeurl.URL("page.app.spaces.space.accounts.account.transactions.transaction.edit", "spaceID", props.SpaceID, "accountID", props.AccountID, "transactionID", props.Transaction.ID),
-					Class:   "flex items-center gap-2",
-				}) {
-					@icon.Pencil(icon.Props{Class: "size-4"})
-					Edit
+				if props.RelatedTransaction == nil {
+					@button.Button(button.Props{
+						Variant: button.VariantDefault,
+						Href:    routeurl.URL("page.app.spaces.space.accounts.account.transactions.transaction.edit", "spaceID", props.SpaceID, "accountID", props.AccountID, "transactionID", props.Transaction.ID),
+						Class:   "flex items-center gap-2",
+					}) {
+						@icon.Pencil(icon.Props{Class: "size-4"})
+						Edit
+					}
 				}
 			</div>
 			@card.Card() {
@@ -100,6 +104,23 @@ templ SpaceTransactionPage(props SpaceTransactionPageProps) {
 							<p class="whitespace-pre-wrap">{ *props.Transaction.Description }</p>
 						</div>
 					}
+					if props.RelatedTransaction != nil && props.RelatedAccount != nil {
+						{{
+							direction := "to"
+							if props.Transaction.Type == model.TransactionTypeDeposit {
+								direction = "from"
+							}
+						}}
+						<div>
+							<p class="text-sm text-muted-foreground">Transferred { direction }</p>
+							<a
+								class="font-medium underline-offset-2 hover:underline"
+								href={ templ.SafeURL(routeurl.URL("page.app.spaces.space.accounts.account.transactions.transaction", "spaceID", props.SpaceID, "accountID", props.RelatedAccount.ID, "transactionID", props.RelatedTransaction.ID)) }
+							>
+								{ props.RelatedAccount.Name }
+							</a>
+						</div>
+					}
 				}
 			}
 			@card.Card() {