fix: availability date is now enforced to not be earlier than the month of the transaction (#789)

Resolves #768.

Author: morremeyer

pkg/models/account_test.go

@@ -59,6 +59,7 @@ func (suite *TestSuiteStandard) TestAccountCalculations() {
 		SourceAccountID:      externalAccount.ID,
 		DestinationAccountID: account.ID,
 		Amount:               decimal.NewFromFloat(100),
+		Date:                 time.Now(),
 		AvailableFrom:        types.MonthOf(time.Now()).AddDate(0, 1),
 		Note:                 "Future Income Transaction",
 	})

pkg/models/transaction.go

@@ -90,6 +90,8 @@ func (t *Transaction) BeforeSave(tx *gorm.DB) (err error) {
 	// Default the AvailableForBudget date to the transaction date
 	if t.AvailableFrom.IsZero() {
 		t.AvailableFrom = types.MonthOf(t.Date)
+	} else if t.AvailableFrom.Before(types.MonthOf(t.Date)) {
+		return fmt.Errorf("availability month must not be earlier than the month of the transaction, transaction date: %s, available month %s", t.Date, t.AvailableFrom)
 	}
 
 	// Enforce ReconciledSource = false when source account is external

pkg/models/transaction_test.go

@@ -5,6 +5,7 @@ import (
 	"testing"
 	"time"
 
+	"github.com/envelope-zero/backend/v3/internal/types"
 	"github.com/envelope-zero/backend/v3/pkg/models"
 	"github.com/google/uuid"
 	"github.com/stretchr/testify/assert"
@@ -120,3 +121,24 @@ func (suite *TestSuiteStandard) TestTransactionReconciled() {
 func (suite *TestSuiteStandard) TestTransactionSelf() {
 	assert.Equal(suite.T(), "Transaction", models.Transaction{}.Self())
 }
+
+// Regression test for https://github.com/envelope-zero/backend/issues/768
+func (suite *TestSuiteStandard) TestTransactionAvailableFromDate() {
+	budget := suite.createTestBudget(models.BudgetCreate{})
+	internalAccount := suite.createTestAccount(models.AccountCreate{External: false, BudgetID: budget.ID})
+	externalAccount := suite.createTestAccount(models.AccountCreate{External: true, BudgetID: budget.ID})
+
+	transaction := models.Transaction{
+		TransactionCreate: models.TransactionCreate{
+			SourceAccountID:      externalAccount.ID,
+			DestinationAccountID: internalAccount.ID,
+			Note:                 "TestTransactionAvailableFromDate",
+			AvailableFrom:        types.NewMonth(2023, 9),
+			Date:                 time.Date(2023, 10, 7, 0, 0, 0, 0, time.UTC),
+		},
+	}
+
+	err := suite.db.Save(&transaction).Error
+	suite.Assert().NotNil(err, "Saving a transaction with an AvailableFrom date in a month before the transaction date should not be possible")
+	suite.Assert().Contains(err.Error(), "availability month must not be earlier than the month of the transaction")
+}