clean-architecture-go-v2/usecase/loan/service.go

package loan

import (
	"github.com/eminetto/clean-architecture-go-v2/entity"
	"github.com/eminetto/clean-architecture-go-v2/usecase/book"
	"github.com/eminetto/clean-architecture-go-v2/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 entity.ErrNotEnoughBooks
	}

	err = u.AddBook(b.ID)
	if err != nil {
		return err
	}
	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 {
		_, err := u.GetBook(b.ID)
		if err != nil {
			continue
		}
		borrowed = true
		borrowedBy = u.ID
		break
	}
	if !borrowed {
		return entity.ErrBookNotBorrowed
	}
	u, err := s.userService.GetUser(borrowedBy)
	if err != nil {
		return err
	}
	err = u.RemoveBook(b.ID)
	if err != nil {
		return err
	}
	err = s.userService.UpdateUser(u)
	if err != nil {
		return err
	}
	b.Quantity++
	err = s.bookService.UpdateBook(b)
	if err != nil {
		return err
	}

	return nil
}