feat: pay bills

internal/service/transaction.go

@@ -0,0 +1,98 @@
+package service
+
+import (
+	"fmt"
+	"strings"
+	"time"
+
+	"git.juancwu.dev/juancwu/budgit/internal/model"
+	"git.juancwu.dev/juancwu/budgit/internal/repository"
+	"github.com/google/uuid"
+	"github.com/shopspring/decimal"
+)
+
+type TransactionService struct {
+	transactionRepo repository.TransactionRepository
+	categoryRepo    repository.CategoryRepository
+	accountService  *AccountService
+}
+
+func NewTransactionService(
+	transactionRepo repository.TransactionRepository,
+	categoryRepo repository.CategoryRepository,
+	accountService *AccountService,
+) *TransactionService {
+	return &TransactionService{
+		transactionRepo: transactionRepo,
+		categoryRepo:    categoryRepo,
+		accountService:  accountService,
+	}
+}
+
+type PayBillInput struct {
+	AccountID   string
+	Title       string
+	Amount      decimal.Decimal
+	OccurredAt  time.Time
+	Description string
+	CategoryID  string
+}
+
+func (s *TransactionService) PayBill(input PayBillInput) (*model.Transaction, error) {
+	title := strings.TrimSpace(input.Title)
+	if title == "" {
+		return nil, fmt.Errorf("title is required")
+	}
+	if input.AccountID == "" {
+		return nil, fmt.Errorf("account id is required")
+	}
+	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")
+	}
+
+	account, err := s.accountService.GetAccount(input.AccountID)
+	if err != nil {
+		return nil, fmt.Errorf("failed to load account: %w", err)
+	}
+
+	newBalance := account.Balance.Sub(input.Amount)
+
+	now := time.Now()
+	var description *string
+	if d := strings.TrimSpace(input.Description); d != "" {
+		description = &d
+	}
+	var categoryID *string
+	if c := strings.TrimSpace(input.CategoryID); c != "" {
+		categoryID = &c
+	}
+
+	txn := &model.Transaction{
+		ID:          uuid.NewString(),
+		Value:       input.Amount,
+		Type:        model.TransactionTypeWithdrawal,
+		AccountID:   input.AccountID,
+		Title:       title,
+		Description: description,
+		OccurredAt:  input.OccurredAt,
+		CreatedAt:   now,
+		UpdatedAt:   now,
+	}
+
+	if err := s.transactionRepo.CreateBillAtomic(txn, newBalance, categoryID); err != nil {
+		return nil, fmt.Errorf("failed to create bill transaction: %w", err)
+	}
+
+	return txn, nil
+}
+
+func (s *TransactionService) ListCategories() ([]*model.Category, error) {
+	categories, err := s.categoryRepo.All()
+	if err != nil {
+		return nil, fmt.Errorf("failed to list categories: %w", err)
+	}
+	return categories, nil
+}