package usecase

import (
	"context"
	"errors"
	"time"

	"github.com/golang-jwt/jwt/v5"
	"golang.org/x/crypto/bcrypt"

	"github.com/gofrs/uuid/v5"

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

// Repository defines DB contract for the core entities.
type Repository interface {
	CreateCompany(ctx context.Context, company *domain.Company) error
	ListCompanies(ctx context.Context) ([]domain.Company, error)
	GetCompany(ctx context.Context, id uuid.UUID) (*domain.Company, error)
	UpdateCompany(ctx context.Context, company *domain.Company) error

	CreateProduct(ctx context.Context, product *domain.Product) error
	ListProducts(ctx context.Context) ([]domain.Product, error)

	CreateOrder(ctx context.Context, order *domain.Order) error
	GetOrder(ctx context.Context, id uuid.UUID) (*domain.Order, error)
	UpdateOrderStatus(ctx context.Context, id uuid.UUID, status domain.OrderStatus) error

	CreateUser(ctx context.Context, user *domain.User) error
	ListUsers(ctx context.Context, filter domain.UserFilter) ([]domain.User, int64, error)
	GetUser(ctx context.Context, id uuid.UUID) (*domain.User, error)
	GetUserByEmail(ctx context.Context, email string) (*domain.User, error)
	UpdateUser(ctx context.Context, user *domain.User) error
	DeleteUser(ctx context.Context, id uuid.UUID) error
}

// PaymentGateway abstracts Mercado Pago integration.
type PaymentGateway interface {
	CreatePreference(ctx context.Context, order *domain.Order) (*domain.PaymentPreference, error)
}

type Service struct {
	repo      Repository
	pay       PaymentGateway
	jwtSecret []byte
	tokenTTL  time.Duration
}

// NewService wires use cases together.
func NewService(repo Repository, pay PaymentGateway, jwtSecret string, tokenTTL time.Duration) *Service {
	return &Service{repo: repo, pay: pay, jwtSecret: []byte(jwtSecret), tokenTTL: tokenTTL}
}

func (s *Service) RegisterCompany(ctx context.Context, company *domain.Company) error {
	company.ID = uuid.Must(uuid.NewV7())
	return s.repo.CreateCompany(ctx, company)
}

func (s *Service) ListCompanies(ctx context.Context) ([]domain.Company, error) {
	return s.repo.ListCompanies(ctx)
}

func (s *Service) GetCompany(ctx context.Context, id uuid.UUID) (*domain.Company, error) {
	return s.repo.GetCompany(ctx, id)
}

func (s *Service) RegisterProduct(ctx context.Context, product *domain.Product) error {
	product.ID = uuid.Must(uuid.NewV7())
	return s.repo.CreateProduct(ctx, product)
}

func (s *Service) ListProducts(ctx context.Context) ([]domain.Product, error) {
	return s.repo.ListProducts(ctx)
}

func (s *Service) CreateOrder(ctx context.Context, order *domain.Order) error {
	order.ID = uuid.Must(uuid.NewV7())
	order.Status = domain.OrderStatusPending
	return s.repo.CreateOrder(ctx, order)
}

func (s *Service) GetOrder(ctx context.Context, id uuid.UUID) (*domain.Order, error) {
	return s.repo.GetOrder(ctx, id)
}

func (s *Service) UpdateOrderStatus(ctx context.Context, id uuid.UUID, status domain.OrderStatus) error {
	return s.repo.UpdateOrderStatus(ctx, id, status)
}

func (s *Service) CreatePaymentPreference(ctx context.Context, id uuid.UUID) (*domain.PaymentPreference, error) {
	order, err := s.repo.GetOrder(ctx, id)
	if err != nil {
		return nil, err
	}
	return s.pay.CreatePreference(ctx, order)
}

func (s *Service) CreateUser(ctx context.Context, user *domain.User, password string) error {
	hashed, err := bcrypt.GenerateFromPassword([]byte(password), bcrypt.DefaultCost)
	if err != nil {
		return err
	}

	user.ID = uuid.Must(uuid.NewV7())
	user.PasswordHash = string(hashed)

	return s.repo.CreateUser(ctx, user)
}

func (s *Service) ListUsers(ctx context.Context, filter domain.UserFilter, page, pageSize int) (*domain.UserPage, error) {
	if page < 1 {
		page = 1
	}
	if pageSize <= 0 {
		pageSize = 20
	}

	filter.Limit = pageSize
	filter.Offset = (page - 1) * pageSize

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

	return &domain.UserPage{Users: users, Total: total, Page: page, PageSize: pageSize}, nil
}

func (s *Service) GetUser(ctx context.Context, id uuid.UUID) (*domain.User, error) {
	return s.repo.GetUser(ctx, id)
}

func (s *Service) UpdateUser(ctx context.Context, user *domain.User, newPassword string) error {
	if newPassword != "" {
		hashed, err := bcrypt.GenerateFromPassword([]byte(newPassword), bcrypt.DefaultCost)
		if err != nil {
			return err
		}
		user.PasswordHash = string(hashed)
	}

	return s.repo.UpdateUser(ctx, user)
}

func (s *Service) DeleteUser(ctx context.Context, id uuid.UUID) error {
	return s.repo.DeleteUser(ctx, id)
}

// RegisterAccount creates a company when needed and persists a user bound to it.
func (s *Service) RegisterAccount(ctx context.Context, company *domain.Company, user *domain.User, password string) error {
	if company != nil {
		if company.ID == uuid.Nil {
			company.ID = uuid.Must(uuid.NewV7())
			company.IsVerified = false
			if err := s.repo.CreateCompany(ctx, company); err != nil {
				return err
			}
		} else {
			if _, err := s.repo.GetCompany(ctx, company.ID); err != nil {
				return err
			}
		}
		user.CompanyID = company.ID
	}

	return s.CreateUser(ctx, user, password)
}

// Authenticate validates credentials and emits a signed JWT.
func (s *Service) Authenticate(ctx context.Context, email, password string) (string, time.Time, error) {
	user, err := s.repo.GetUserByEmail(ctx, email)
	if err != nil {
		return "", time.Time{}, err
	}

	if err := bcrypt.CompareHashAndPassword([]byte(user.PasswordHash), []byte(password)); err != nil {
		return "", time.Time{}, errors.New("invalid credentials")
	}

	expiresAt := time.Now().Add(s.tokenTTL)
	claims := jwt.MapClaims{
		"sub":        user.ID.String(),
		"role":       user.Role,
		"company_id": user.CompanyID.String(),
		"exp":        expiresAt.Unix(),
	}

	token := jwt.NewWithClaims(jwt.SigningMethodHS256, claims)
	signed, err := token.SignedString(s.jwtSecret)
	if err != nil {
		return "", time.Time{}, err
	}

	return signed, expiresAt, nil
}

// VerifyCompany marks a company as verified.
func (s *Service) VerifyCompany(ctx context.Context, id uuid.UUID) (*domain.Company, error) {
	company, err := s.repo.GetCompany(ctx, id)
	if err != nil {
		return nil, err
	}
	company.IsVerified = true

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