feat: set billing customer credit min limit (#781)

- If a billing account credit min limit is set less then 0,
it works as overdraft. Default is 0.
- If a org billing account is in overdraft state, it's not
allowed to create new billing account unless the dues are
settled.
- Setting this limit more then 0 works as min purchase requirement
for the account.
- Only platform admins can change the account limits.
- raystack/proton#370

Signed-off-by: Kush Sharma <[email protected]>

Makefile

@@ -4,7 +4,7 @@ TAG := $(shell git rev-list --tags --max-count=1)
 VERSION := $(shell git describe --tags ${TAG})
 .PHONY: build check fmt lint test test-race vet test-cover-html help install proto ui compose-up-dev
 .DEFAULT_GOAL := build
-PROTON_COMMIT := "37eef9d41df218eb19d07a3b7f75d089c328c575"
+PROTON_COMMIT := "145667ee53b037d636c09df0a529c351069132dc"
 
 ui:
 	@echo " > generating ui build"

billing/credit/service.go

@@ -74,17 +74,6 @@ func (s Service) Deduct(ctx context.Context, cred Credit) error {
 		return errors.New("credit amount is negative")
 	}
 
-	// check balance, if enough, sub credits
-	currentBalance, err := s.GetBalance(ctx, cred.CustomerID)
-	if err != nil {
-		return fmt.Errorf("failed to apply transaction: %w", err)
-	}
-	// TODO(kushsharma): this is prone to timing attacks and better we do this
-	// in a transaction
-	if currentBalance < cred.Amount {
-		return ErrInsufficientCredits
-	}
-
 	txSource := "system"
 	if cred.Source != "" {
 		txSource = cred.Source
@@ -110,6 +99,8 @@ func (s Service) Deduct(ctx context.Context, cred Credit) error {
 	}); err != nil {
 		if errors.Is(err, ErrAlreadyApplied) {
 			return ErrAlreadyApplied
+		} else if errors.Is(err, ErrInsufficientCredits) {
+			return ErrInsufficientCredits
 		}
 		return fmt.Errorf("failed to deduct credits: %w", err)
 	}

billing/credit/service_test.go

@@ -291,27 +291,10 @@ func TestService_Deduct(t *testing.T) {
 
 			setup: func() *credit.Service {
 				s, mockTransactionRepo := mockService(t)
-				mockTransactionRepo.EXPECT().GetBalance(ctx, "customer_id").Return(10, nil)
 				mockTransactionRepo.EXPECT().CreateEntry(ctx, mock.Anything, mock.Anything).Return(nil, credit.ErrAlreadyApplied)
 				return s
 			},
 		},
-		{
-			name: "should return an error if balance cannot be fetched",
-			args: args{
-				cred: credit.Credit{
-					ID:         "12",
-					CustomerID: "customer_id",
-					Amount:     10,
-				},
-			},
-			want: errors.New(fmt.Sprintf("failed to apply transaction: %v", dummyError)),
-			setup: func() *credit.Service {
-				s, mockTransactionRepo := mockService(t)
-				mockTransactionRepo.EXPECT().GetBalance(ctx, "customer_id").Return(0, dummyError)
-				return s
-			},
-		},
 		{
 			name: "should return ErrInsufficientCredits error if customer's balance is less than transaction amount",
 			args: args{
@@ -324,7 +307,7 @@ func TestService_Deduct(t *testing.T) {
 			want: credit.ErrInsufficientCredits,
 			setup: func() *credit.Service {
 				s, mockTransactionRepo := mockService(t)
-				mockTransactionRepo.EXPECT().GetBalance(ctx, "customer_id").Return(5, nil)
+				mockTransactionRepo.EXPECT().CreateEntry(ctx, mock.Anything, mock.Anything).Return(nil, credit.ErrInsufficientCredits)
 				return s
 			},
 		},
@@ -340,7 +323,6 @@ func TestService_Deduct(t *testing.T) {
 			want: errors.New(fmt.Sprintf("failed to deduct credits: %v", dummyError)),
 			setup: func() *credit.Service {
 				s, mockTransactionRepo := mockService(t)
-				mockTransactionRepo.EXPECT().GetBalance(ctx, "customer_id").Return(20, nil)
 				mockTransactionRepo.EXPECT().CreateEntry(ctx, mock.Anything, mock.Anything).Return([]credit.Transaction{}, dummyError)
 				return s
 			},
@@ -360,7 +342,6 @@ func TestService_Deduct(t *testing.T) {
 			want: nil,
 			setup: func() *credit.Service {
 				s, mockTransactionRepo := mockService(t)
-				mockTransactionRepo.EXPECT().GetBalance(ctx, "customer_id").Return(20, nil)
 				mockTransactionRepo.EXPECT().CreateEntry(ctx, credit.Transaction{ID: "12", CustomerID: "customer_id", Type: credit.DebitType, Amount: 10, Source: "system", Metadata: metadata.Metadata{"a": "a"}}, credit.Transaction{Type: credit.CreditType, CustomerID: schema.PlatformOrgID.String(), Amount: 10, Source: "system", Metadata: metadata.Metadata{"a": "a"}}).Return([]credit.Transaction{}, nil)
 				return s
 			},

billing/customer/customer.go

@@ -39,8 +39,9 @@ type Customer struct {
 	Address Address
 	TaxData []Tax
 	// Currency Three-letter ISO 4217 currency code in lower case
-	Currency string `default:"usd"`
-	Metadata metadata.Metadata
+	Currency  string `default:"usd"`
+	Metadata  metadata.Metadata
+	CreditMin int64
 
 	// Stripe specific fields
 	// StripeTestClockID is used for testing purposes only to simulate a subscription

billing/customer/errors.go

@@ -5,11 +5,12 @@ import (
 )
 
 var (
-	ErrNotFound       = errors.New("customer not found")
-	ErrInvalidUUID    = errors.New("invalid syntax of uuid")
-	ErrInvalidID      = errors.New("billing customer id is invalid")
-	ErrConflict       = errors.New("customer already exist")
-	ErrActiveConflict = errors.New("an active account already exists for the organization")
-	ErrInvalidDetail  = errors.New("invalid billing customer detail")
-	ErrDisabled       = errors.New("billing customer is disabled")
+	ErrNotFound                       = errors.New("customer not found")
+	ErrInvalidUUID                    = errors.New("invalid syntax of uuid")
+	ErrInvalidID                      = errors.New("billing customer id is invalid")
+	ErrConflict                       = errors.New("customer already exist")
+	ErrActiveConflict                 = errors.New("an active account already exists for the organization")
+	ErrInvalidDetail                  = errors.New("invalid billing customer detail")
+	ErrDisabled                       = errors.New("billing customer is disabled")
+	ErrExistingAccountWithPendingDues = errors.New("existing account with pending dues found")
 )

billing/customer/service.go

@@ -7,6 +7,8 @@ import (
 	"sync"
 	"time"
 
+	"github.com/raystack/frontier/pkg/utils"
+
 	"github.com/robfig/cron/v3"
 	"github.com/stripe/stripe-go/v79"
 
@@ -28,23 +30,31 @@ type Repository interface {
 	Create(ctx context.Context, customer Customer) (Customer, error)
 	UpdateByID(ctx context.Context, customer Customer) (Customer, error)
 	Delete(ctx context.Context, id string) error
+	UpdateCreditMinByID(ctx context.Context, customerID string, limit int64) (Customer, error)
+}
+
+type CreditService interface {
+	GetBalance(ctx context.Context, id string) (int64, error)
 }
 
 type Service struct {
-	stripeClient *client.API
-	repository   Repository
+	stripeClient  *client.API
+	repository    Repository
+	creditService CreditService
 
 	syncJob   *cron.Cron
 	mu        sync.Mutex
 	syncDelay time.Duration
 }
 
-func NewService(stripeClient *client.API, repository Repository, cfg billing.Config) *Service {
+func NewService(stripeClient *client.API, repository Repository, cfg billing.Config,
+	creditService CreditService) *Service {
 	return &Service{
-		stripeClient: stripeClient,
-		repository:   repository,
-		mu:           sync.Mutex{},
-		syncDelay:    cfg.RefreshInterval.Customer,
+		stripeClient:  stripeClient,
+		repository:    repository,
+		mu:            sync.Mutex{},
+		syncDelay:     cfg.RefreshInterval.Customer,
+		creditService: creditService,
 	}
 }
 
@@ -57,15 +67,25 @@ func (s *Service) Create(ctx context.Context, customer Customer, offline bool) (
 	// do not allow creating a new customer account if there exists already an active billing account
 	existingAccounts, err := s.repository.List(ctx, Filter{
 		OrgID: customer.OrgID,
-		State: ActiveState,
 	})
 	if err != nil {
 		return Customer{}, err
 	}
-	if len(existingAccounts) > 0 {
+	activeAccounts := utils.Filter(existingAccounts, func(i Customer) bool {
+		return i.State == ActiveState
+	})
+	if len(activeAccounts) > 0 {
 		return Customer{}, ErrActiveConflict
 	}
 
+	// do not allow creating account if the balance of a previous account within org
+	// is less than 0
+	for _, account := range existingAccounts {
+		if balance, err := s.creditService.GetBalance(ctx, account.ID); err == nil && balance < 0 {
+			return Customer{}, ErrExistingAccountWithPendingDues
+		}
+	}
+
 	// offline mode, we don't need to create the customer in billing provider
 	if !offline {
 		stripeCustomer, err := s.RegisterToProvider(ctx, customer)
@@ -482,3 +502,7 @@ func (s *Service) TriggerSyncByProviderID(ctx context.Context, id string) error
 	}
 	return s.SyncWithProvider(ctx, customrs[0])
 }
+
+func (s *Service) UpdateCreditMinByID(ctx context.Context, customerID string, limit int64) (Customer, error) {
+	return s.repository.UpdateCreditMinByID(ctx, customerID, limit)
+}