package service

import (
	"context"
	"errors"
	"strings"

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

var (
	ErrInvalidTransactionType   = errors.New("type must be 'income' or 'expense'")
	ErrTransactionEmptyDesc     = errors.New("description is required")
	ErrTransactionInvalidAmount = errors.New("amount must be greater than zero")
)

type TransactionService struct {
	repo repository.ManualTransactionRepository
}

func NewTransactionService(repo repository.ManualTransactionRepository) *TransactionService {
	return &TransactionService{repo: repo}
}

func (s *TransactionService) List(ctx context.Context, month string) ([]model.Transaction, error) {
	txs, err := s.repo.List(ctx, month)
	if txs == nil {
		return []model.Transaction{}, err
	}
	return txs, err
}

func (s *TransactionService) Create(ctx context.Context, t model.Transaction) (*model.Transaction, error) {
	if err := validateTransaction(t); err != nil {
		return nil, err
	}
	t.Description = strings.TrimSpace(t.Description)
	return s.repo.Create(ctx, t)
}

func (s *TransactionService) Update(ctx context.Context, t model.Transaction) (*model.Transaction, error) {
	if err := validateTransaction(t); err != nil {
		return nil, err
	}
	t.Description = strings.TrimSpace(t.Description)
	out, err := s.repo.Update(ctx, t)
	if errors.Is(err, repository.ErrNotFound) {
		return nil, errors.New("transaction not found")
	}
	return out, err
}

func (s *TransactionService) Delete(ctx context.Context, id int) error {
	err := s.repo.Delete(ctx, id)
	if errors.Is(err, repository.ErrNotFound) {
		return errors.New("transaction not found")
	}
	return err
}

func (s *TransactionService) DeleteByMonth(ctx context.Context, month string) (int, error) {
	return s.repo.DeleteByMonth(ctx, month)
}

func validateTransaction(t model.Transaction) error {
	if strings.TrimSpace(t.Description) == "" {
		return ErrTransactionEmptyDesc
	}
	if t.Amount <= 0 {
		return ErrTransactionInvalidAmount
	}
	if t.Type != "income" && t.Type != "expense" {
		return ErrInvalidTransactionType
	}
	return nil
}