3ybactuk-marketplace-go-service-project/cart/internal/domain/cart/service/service.go

package service

import (
	"context"
	"fmt"
	"slices"
	"sync"

	"route256/cart/internal/domain/entity"
	"route256/cart/internal/domain/model"

	"github.com/rs/zerolog/log"
)

type Repository interface {
	AddItem(ctx context.Context, userID entity.UID, item *model.Item) error
	GetItemsByUserID(ctx context.Context, userID entity.UID) (entity.Cart, error)
	DeleteItem(ctx context.Context, userID entity.UID, sku entity.Sku) error
	DeleteItemsByUserID(ctx context.Context, userID entity.UID) error
}

type ProductService interface {
	GetProductBySku(ctx context.Context, sku entity.Sku) (*model.Product, error)
}

type CartService struct {
	repository     Repository
	productService ProductService
}

func NewCartService(repository Repository, productService ProductService) *CartService {
	return &CartService{
		repository:     repository,
		productService: productService,
	}
}

func (s *CartService) AddItem(ctx context.Context, userID entity.UID, item *model.Item) error {
	if err := item.Validate(); err != nil {
		return fmt.Errorf("invalid requested values: %w", err)
	}

	if userID <= 0 {
		return fmt.Errorf("invalid userID")
	}

	_, err := s.productService.GetProductBySku(ctx, item.Product.Sku)
	if err != nil {
		return fmt.Errorf("productService.GetProductBySku: %w", err)
	}

	if err := s.repository.AddItem(ctx, userID, item); err != nil {
		return fmt.Errorf("repository.AddItemToCart: %w", err)
	}

	return nil
}

// GetUserCart gets all user cart's item ids, gets the item description from the product-service
// and return a list of the collected items.
// In case of failed request to product-service, return nothing and error.
//
// TODO: add worker group, BUT it's OK for now,
// assuming user does not have hundreds of different items in his cart.
func (s *CartService) GetItemsByUserID(ctx context.Context, userID entity.UID) (*model.Cart, error) {
	if userID <= 0 {
		return nil, fmt.Errorf("userID invalid")
	}

	cart, err := s.repository.GetItemsByUserID(ctx, userID)
	if err != nil {
		return nil, fmt.Errorf("repository.AddItemToCart: %w", err)
	}

	if len(cart.Items) == 0 {
		return nil, model.ErrCartNotFound
	}

	ctx, cancel := context.WithCancel(ctx)
	defer cancel()

	resultCart := &model.Cart{
		UserID:     userID,
		Items:      make([]*model.Item, len(cart.Items)),
		TotalPrice: 0,
	}

	errCh := make(chan error, 1)

	var wg sync.WaitGroup

	for idx, sku := range cart.Items {
		wg.Add(1)

		go func(sku entity.Sku, count uint32, idx int) {
			defer wg.Done()

			product, err := s.productService.GetProductBySku(ctx, sku)
			if err != nil {
				select {
				case errCh <- fmt.Errorf("productService.GetProductBySku: %w", err):
				case <-ctx.Done():
				}

				log.Error().Err(err).Msg("productService.GetProductBySku")

				return
			}

			resultCart.Items[idx] = &model.Item{
				Product: product,
				Count:   count,
			}
			resultCart.TotalPrice += uint32(product.Price) * count
		}(sku, cart.ItemCount[sku], idx)
	}

	doneCh := make(chan struct{})
	go func() {
		wg.Wait()

		close(doneCh)
	}()

	select {
	case err := <-errCh:
		cancel()

		return nil, err
	case <-doneCh:
		slices.SortStableFunc(resultCart.Items, func(a, b *model.Item) int {
			return int(a.Product.Sku - b.Product.Sku)
		})

		return resultCart, nil
	}
}

func (s *CartService) DeleteItem(ctx context.Context, userID entity.UID, sku entity.Sku) error {
	if userID <= 0 {
		return fmt.Errorf("userID invalid")
	}

	if sku <= 0 {
		return fmt.Errorf("sku invalid")
	}

	if err := s.repository.DeleteItem(ctx, userID, sku); err != nil {
		return fmt.Errorf("repository.DeleteItemFromUserCart: %w", err)
	}

	return nil
}

func (s *CartService) DeleteItemsByUserID(ctx context.Context, userID entity.UID) error {
	if userID <= 0 {
		return fmt.Errorf("userID invalid")
	}

	if err := s.repository.DeleteItemsByUserID(ctx, userID); err != nil {
		return fmt.Errorf("repository.DeleteUserCart: %w", err)
	}

	return nil
}