package service

import (
	"context"
	"errors"
	"strings"

	"financeiro-carvalho/internal/model"
	"financeiro-carvalho/internal/repository"
)

var (
	ErrDefaultCategory   = errors.New("default categories cannot be deleted")
	ErrHasTransactions   = errors.New("category has linked transactions")
	ErrEmptyName         = errors.New("name is required")
	ErrInvalidColor      = errors.New("color must be a valid hex color (e.g. #FF5733)")
)

type CategoryService struct {
	repo repository.CategoryRepository
}

func NewCategoryService(repo repository.CategoryRepository) *CategoryService {
	return &CategoryService{repo: repo}
}

func (s *CategoryService) List(ctx context.Context) ([]model.Category, error) {
	return s.repo.List(ctx)
}

func (s *CategoryService) Create(ctx context.Context, in model.CategoryInput) (*model.Category, error) {
	if err := validateInput(in); err != nil {
		return nil, err
	}
	return s.repo.Create(ctx, strings.TrimSpace(in.Name), in.Color, in.IsTax)
}

func (s *CategoryService) Update(ctx context.Context, id int, in model.CategoryInput) (*model.Category, error) {
	if err := validateInput(in); err != nil {
		return nil, err
	}
	return s.repo.Update(ctx, id, strings.TrimSpace(in.Name), in.Color, in.IsTax)
}

func (s *CategoryService) Delete(ctx context.Context, id int) error {
	cat, err := s.repo.GetByID(ctx, id)
	if err != nil {
		return err
	}
	if cat.IsDefault {
		return ErrDefaultCategory
	}
	hasTx, err := s.repo.HasTransactions(ctx, id)
	if err != nil {
		return err
	}
	if hasTx {
		return ErrHasTransactions
	}
	return s.repo.Delete(ctx, id)
}

func validateInput(in model.CategoryInput) error {
	if strings.TrimSpace(in.Name) == "" {
		return ErrEmptyName
	}
	if !isValidHexColor(in.Color) {
		return ErrInvalidColor
	}
	return nil
}

func isValidHexColor(c string) bool {
	if len(c) != 7 || c[0] != '#' {
		return false
	}
	for _, ch := range c[1:] {
		if !((ch >= '0' && ch <= '9') || (ch >= 'a' && ch <= 'f') || (ch >= 'A' && ch <= 'F')) {
			return false
		}
	}
	return true
}