feat: improvements in structures

domain/usecase/loan/service.go

@@ -0,0 +1,101 @@
+package loan
+
+import (
+	"github.com/eminetto/clean-architecture-go-v2/domain"
+	"github.com/eminetto/clean-architecture-go-v2/domain/entity"
+	"github.com/eminetto/clean-architecture-go-v2/domain/usecase/book"
+	"github.com/eminetto/clean-architecture-go-v2/domain/usecase/user"
+)
+
+//Service loan usecase
+type Service struct {
+	userService user.UseCase
+	bookService book.UseCase
+}
+
+//NewService create new use case
+func NewService(u user.UseCase, b book.UseCase) *Service {
+	return &Service{
+		userService: u,
+		bookService: b,
+	}
+}
+
+//Borrow borrow a book to an user
+func (s *Service) Borrow(u *entity.User, b *entity.Book) error {
+	u, err := s.userService.GetUser(u.ID)
+	if err != nil {
+		return err
+	}
+	b, err = s.bookService.GetBook(b.ID)
+	if err != nil {
+		return err
+	}
+	if b.Quantity <= 0 {
+		return domain.ErrNotEnoughBooks
+	}
+	for _, v := range u.Books {
+		if v == b.ID {
+			return domain.ErrBookAlreadyBorrowed
+		}
+	}
+	u.Books = append(u.Books, b.ID)
+	err = s.userService.UpdateUser(u)
+	if err != nil {
+		return err
+	}
+	b.Quantity--
+	err = s.bookService.UpdateBook(b)
+	if err != nil {
+		return err
+	}
+	return nil
+}
+
+//Return return a book
+func (s *Service) Return(b *entity.Book) error {
+	b, err := s.bookService.GetBook(b.ID)
+	if err != nil {
+		return err
+	}
+
+	all, err := s.userService.ListUsers()
+	if err != nil {
+		return err
+	}
+	borrowed := false
+	var borrowedBy entity.ID
+	for _, u := range all {
+		for _, bookID := range u.Books {
+			if bookID == b.ID {
+				borrowed = true
+				borrowedBy = u.ID
+				break
+			}
+		}
+	}
+	if !borrowed {
+		return domain.ErrBookNotBorrowed
+	}
+	u, err := s.userService.GetUser(borrowedBy)
+	if err != nil {
+		return err
+	}
+	for i, j := range u.Books {
+		if j == b.ID {
+			u.Books = append(u.Books[:i], u.Books[i+1:]...)
+			err = s.userService.UpdateUser(u)
+			if err != nil {
+				return err
+			}
+			break
+		}
+	}
+	b.Quantity++
+	err = s.bookService.UpdateBook(b)
+	if err != nil {
+		return err
+	}
+
+	return nil
+}