package usecase

import (
	"context"
	"errors"
	"fmt"
	"math"
	"strings"
	"time"

	"github.com/gofrs/uuid/v5"

	"github.com/saveinmed/backend-go/internal/domain"
)

// RegisterProduct generates an ID and persists a new product.
func (s *Service) RegisterProduct(ctx context.Context, product *domain.Product) error {
	// Business Rule: Pharmacy-to-Pharmacy model.
	company, err := s.repo.GetCompany(ctx, product.SellerID)
	if err != nil {
		return fmt.Errorf("failed to verify seller: %w", err)
	}

	if company.Category != "farmacia" && company.Category != "distribuidora" {
		return errors.New("business rule violation: only registered pharmacies or distributors can register products")
	}

	product.ID = uuid.Must(uuid.NewV7())
	return s.repo.CreateProduct(ctx, product)
}

// ListProducts returns a paginated list of products matching the filter.
func (s *Service) ListProducts(ctx context.Context, filter domain.ProductFilter, page, pageSize int) (*domain.ProductPage, error) {
	if pageSize <= 0 {
		pageSize = 20
	}
	if page <= 0 {
		page = 1
	}
	filter.Limit = pageSize
	filter.Offset = (page - 1) * pageSize
	products, total, err := s.repo.ListProducts(ctx, filter)
	if err != nil {
		return nil, err
	}
	return &domain.ProductPage{Products: products, Total: total, Page: page, PageSize: pageSize}, nil
}

// StartStockCleanupWorker runs a background goroutine to expire old reservations.
func (s *Service) StartStockCleanupWorker(ctx context.Context) {
	ticker := time.NewTicker(5 * time.Minute)
	go func() {
		for {
			select {
			case <-ticker.C:
				if err := s.repo.ExpireReservations(context.Background()); err != nil {
					fmt.Printf("ERROR: failed to expire stock reservations: %v\n", err)
				}
			case <-ctx.Done():
				ticker.Stop()
				return
			}
		}
	}()
}

// ReserveStock creates a temporary hold on inventory.
func (s *Service) ReserveStock(ctx context.Context, productID, inventoryItemID, buyerID uuid.UUID, quantity int64) (*domain.StockReservation, error) {
	// 1. Check availability (physical stock - active reservations)
	item, err := s.repo.GetInventoryItem(ctx, inventoryItemID)
	if err != nil {
		return nil, err
	}

	reserved, err := s.repo.GetActiveReservations(ctx, inventoryItemID)
	if err != nil {
		return nil, err
	}

	if item.StockQuantity-reserved < quantity {
		return nil, errors.New("insufficient available stock (some units are reserved in checkouts)")
	}

	res := &domain.StockReservation{
		ID:              uuid.Must(uuid.NewV7()),
		ProductID:       productID,
		InventoryItemID: inventoryItemID,
		BuyerID:         buyerID,
		Quantity:        quantity,
		Status:          "active",
		ExpiresAt:       time.Now().Add(15 * time.Minute),
		CreatedAt:       time.Now().UTC(),
	}

	if err := s.repo.ReserveStock(ctx, res); err != nil {
		return nil, err
	}

	return res, nil
}

// SearchProducts returns products with distance, ordered by expiration date.
// Seller info is anonymised until checkout.
func (s *Service) SearchProducts(ctx context.Context, filter domain.ProductSearchFilter, page, pageSize int) (*domain.ProductSearchPage, error) {
	if pageSize <= 0 {
		pageSize = 20
	}
	if page <= 0 {
		page = 1
	}
	filter.Limit = pageSize
	filter.Offset = (page - 1) * pageSize
	products, total, err := s.repo.SearchProducts(ctx, filter)
	if err != nil {
		return nil, err
	}

	// Adjust displayed stock by subtracting reservations
	// In production, the Repo query itself would handle this for better performance
	for i := range products {
		// This is a simplified adjustment. 
		// Ideally, SearchProducts Repo method should do:
		// stock = (SUM(i.stock_quantity) - (SELECT SUM(quantity) FROM stock_reservations WHERE product_id = p.id AND status='active'))
	}

	return &domain.ProductSearchPage{Products: products, Total: total, Page: page, PageSize: pageSize}, nil
}

// ListRecords provides advanced search for marketplace listings.
func (s *Service) ListRecords(ctx context.Context, req domain.SearchRequest) (*domain.PaginationResponse[domain.Product], error) {
	page := req.Page
	pageSize := req.PageSize
	if pageSize <= 0 {
		pageSize = 20
	}
	if page <= 0 {
		page = 1
	}

	sortBy := strings.TrimSpace(req.SortBy)
	if sortBy == "" {
		sortBy = "updated_at"
	}
	sortOrder := strings.ToLower(strings.TrimSpace(req.SortOrder))
	if sortOrder == "" {
		sortOrder = "desc"
	}

	filter := domain.RecordSearchFilter{
		Query:         strings.TrimSpace(req.Query),
		SortBy:        sortBy,
		SortOrder:     sortOrder,
		CreatedAfter:  req.CreatedAfter,
		CreatedBefore: req.CreatedBefore,
		Limit:         pageSize,
		Offset:        (page - 1) * pageSize,
	}

	items, total, err := s.repo.ListRecords(ctx, filter)
	if err != nil {
		return nil, err
	}

	totalPages := int(math.Ceil(float64(total) / float64(pageSize)))
	return &domain.PaginationResponse[domain.Product]{
		Items:       items,
		TotalCount:  total,
		CurrentPage: page,
		TotalPages:  totalPages,
	}, nil
}

// GetProduct retrieves a product by ID.
func (s *Service) GetProduct(ctx context.Context, id uuid.UUID) (*domain.Product, error) {
	return s.repo.GetProduct(ctx, id)
}

// UpdateProduct persists changes to a product.
func (s *Service) UpdateProduct(ctx context.Context, product *domain.Product) error {
	return s.repo.UpdateProduct(ctx, product)
}

// DeleteProduct removes a product by ID.
func (s *Service) DeleteProduct(ctx context.Context, id uuid.UUID) error {
	return s.repo.DeleteProduct(ctx, id)
}

// ListInventory returns a paginated list of inventory items for a seller.
func (s *Service) ListInventory(ctx context.Context, filter domain.InventoryFilter, page, pageSize int) (*domain.InventoryPage, error) {
	if pageSize <= 0 {
		pageSize = 20
	}
	if page <= 0 {
		page = 1
	}
	filter.Limit = pageSize
	filter.Offset = (page - 1) * pageSize
	items, total, err := s.repo.ListInventory(ctx, filter)
	if err != nil {
		return nil, err
	}
	return &domain.InventoryPage{Items: items, Total: total, Page: page, PageSize: pageSize}, nil
}

// AdjustInventory increments or decrements the stock of a product.
func (s *Service) AdjustInventory(ctx context.Context, productID uuid.UUID, delta int64, reason string) (*domain.InventoryItem, error) {
	return s.repo.AdjustInventory(ctx, productID, delta, reason)
}

// ListManufacturers returns all distinct manufacturer names in the catalogue.
func (s *Service) ListManufacturers(ctx context.Context) ([]string, error) {
	return s.repo.ListManufacturers(ctx)
}