package service

import (
	"errors"
	"fmt"

	"accounting-app/internal/models"
)

// Service layer errors for user settings
var (
	ErrInvalidIconLayout       = errors.New("invalid icon layout, must be one of: four, five, six")
	ErrInvalidImageCompression = errors.New("invalid image compression, must be one of: low, medium, high")
	ErrDefaultAccountNotFound  = errors.New("default account not found")
	ErrInvalidDefaultAccount   = errors.New("invalid default account")
)

// UserSettingsRepositoryInterface defines the interface for user settings repository operations
type UserSettingsRepositoryInterface interface {
	GetOrCreate(userID uint) (*models.UserSettings, error)
	Update(settings *models.UserSettings) error
	GetWithDefaultAccounts(userID uint) (*models.UserSettings, error)
}

// AccountRepositoryInterface defines the interface for account repository operations needed by settings service
type AccountRepositoryInterface interface {
	GetByID(userID uint, id uint) (*models.Account, error)
	ExistsByID(userID uint, id uint) (bool, error)
}

// UserSettingsInput represents the input data for updating user settings
type UserSettingsInput struct {
	PreciseTimeEnabled   *bool   `json:"precise_time_enabled"`
	IconLayout           *string `json:"icon_layout"`
	ImageCompression     *string `json:"image_compression"`
	ShowReimbursementBtn *bool   `json:"show_reimbursement_btn"`
	ShowRefundBtn        *bool   `json:"show_refund_btn"`
	CurrentLedgerID      *uint   `json:"current_ledger_id"`
}

// DefaultAccountsInput represents the input data for updating default accounts
// Feature: financial-core-upgrade
// Validates: Requirements 5.1, 5.2
type DefaultAccountsInput struct {
	DefaultExpenseAccountID *uint `json:"default_expense_account_id"`
	DefaultIncomeAccountID  *uint `json:"default_income_account_id"`
}

// DefaultAccountsResponse represents the response for default accounts
// Feature: financial-core-upgrade
// Validates: Requirements 5.1, 5.2
type DefaultAccountsResponse struct {
	DefaultExpenseAccountID *uint           `json:"default_expense_account_id,omitempty"`
	DefaultIncomeAccountID  *uint           `json:"default_income_account_id,omitempty"`
	DefaultExpenseAccount   *models.Account `json:"default_expense_account,omitempty"`
	DefaultIncomeAccount    *models.Account `json:"default_income_account,omitempty"`
}

// UserSettingsServiceInterface defines the interface for user settings service operations
type UserSettingsServiceInterface interface {
	GetSettings(userID uint) (*models.UserSettings, error)
	UpdateSettings(userID uint, input UserSettingsInput) (*models.UserSettings, error)
	GetDefaultAccounts(userID uint) (*DefaultAccountsResponse, error)
	UpdateDefaultAccounts(userID uint, input DefaultAccountsInput) (*DefaultAccountsResponse, error)
	ClearDefaultAccount(userID uint, accountID uint) error
}

// UserSettingsService handles business logic for user settings
type UserSettingsService struct {
	repo        UserSettingsRepositoryInterface
	accountRepo AccountRepositoryInterface
}

// NewUserSettingsService creates a new UserSettingsService instance
func NewUserSettingsService(repo UserSettingsRepositoryInterface) *UserSettingsService {
	return &UserSettingsService{
		repo: repo,
	}
}

// NewUserSettingsServiceWithAccountRepo creates a new UserSettingsService instance with account repository
// Feature: financial-core-upgrade
// Validates: Requirements 5.1, 5.2, 5.6, 5.7, 5.8
func NewUserSettingsServiceWithAccountRepo(repo UserSettingsRepositoryInterface, accountRepo AccountRepositoryInterface) *UserSettingsService {
	return &UserSettingsService{
		repo:        repo,
		accountRepo: accountRepo,
	}
}

// GetSettings retrieves user settings, creating default settings if not found
// Feature: accounting-feature-upgrade
// Validates: Requirements 5.4, 6.5, 8.25-8.27
func (s *UserSettingsService) GetSettings(userID uint) (*models.UserSettings, error) {
	settings, err := s.repo.GetOrCreate(userID)
	if err != nil {
		return nil, fmt.Errorf("failed to get settings: %w", err)
	}
	return settings, nil
}

// UpdateSettings updates user settings with validation
// Feature: accounting-feature-upgrade
// Validates: Requirements 5.4, 6.5, 8.25-8.27
func (s *UserSettingsService) UpdateSettings(userID uint, input UserSettingsInput) (*models.UserSettings, error) {
	// Get existing settings
	settings, err := s.repo.GetOrCreate(userID)
	if err != nil {
		return nil, fmt.Errorf("failed to get settings: %w", err)
	}

	// Validate and update icon layout if provided
	if input.IconLayout != nil {
		layout := *input.IconLayout
		if layout != string(models.IconLayoutFour) &&
			layout != string(models.IconLayoutFive) &&
			layout != string(models.IconLayoutSix) {
			return nil, ErrInvalidIconLayout
		}
		settings.IconLayout = layout
	}

	// Validate and update image compression if provided
	if input.ImageCompression != nil {
		compression := *input.ImageCompression
		if compression != string(models.ImageCompressionLow) &&
			compression != string(models.ImageCompressionMedium) &&
			compression != string(models.ImageCompressionHigh) {
			return nil, ErrInvalidImageCompression
		}
		settings.ImageCompression = compression
	}

	// Update other fields if provided
	if input.PreciseTimeEnabled != nil {
		settings.PreciseTimeEnabled = *input.PreciseTimeEnabled
	}

	if input.ShowReimbursementBtn != nil {
		settings.ShowReimbursementBtn = *input.ShowReimbursementBtn
	}

	if input.ShowRefundBtn != nil {
		settings.ShowRefundBtn = *input.ShowRefundBtn
	}

	if input.CurrentLedgerID != nil {
		settings.CurrentLedgerID = input.CurrentLedgerID
	}

	// Save to database
	if err := s.repo.Update(settings); err != nil {
		return nil, fmt.Errorf("failed to update settings: %w", err)
	}

	return settings, nil
}

// GetDefaultAccounts retrieves the current default account settings
// Feature: financial-core-upgrade
// Validates: Requirements 5.1, 5.2
func (s *UserSettingsService) GetDefaultAccounts(userID uint) (*DefaultAccountsResponse, error) {
	settings, err := s.repo.GetOrCreate(userID)
	if err != nil {
		return nil, fmt.Errorf("failed to get settings: %w", err)
	}

	response := &DefaultAccountsResponse{
		DefaultExpenseAccountID: settings.DefaultExpenseAccountID,
		DefaultIncomeAccountID:  settings.DefaultIncomeAccountID,
	}

	// Load account details if account repo is available
	if s.accountRepo != nil {
		if settings.DefaultExpenseAccountID != nil {
			account, err := s.accountRepo.GetByID(userID, *settings.DefaultExpenseAccountID)
			if err == nil {
				response.DefaultExpenseAccount = account
			}
		}
		if settings.DefaultIncomeAccountID != nil {
			account, err := s.accountRepo.GetByID(userID, *settings.DefaultIncomeAccountID)
			if err == nil {
				response.DefaultIncomeAccount = account
			}
		}
	}

	return response, nil
}

// UpdateDefaultAccounts updates the default account settings
// Feature: financial-core-upgrade
// Validates: Requirements 5.1, 5.2, 5.7, 5.8
func (s *UserSettingsService) UpdateDefaultAccounts(userID uint, input DefaultAccountsInput) (*DefaultAccountsResponse, error) {
	// Get existing settings
	settings, err := s.repo.GetOrCreate(userID)
	if err != nil {
		return nil, fmt.Errorf("failed to get settings: %w", err)
	}

	// Validate and update default expense account if provided
	if input.DefaultExpenseAccountID != nil {
		if *input.DefaultExpenseAccountID == 0 {
			// Clear the default expense account
			settings.DefaultExpenseAccountID = nil
		} else {
			// Validate account exists
			if s.accountRepo != nil {
				exists, err := s.accountRepo.ExistsByID(userID, *input.DefaultExpenseAccountID)
				if err != nil {
					return nil, fmt.Errorf("failed to validate expense account: %w", err)
				}
				if !exists {
					return nil, ErrDefaultAccountNotFound
				}
			}
			settings.DefaultExpenseAccountID = input.DefaultExpenseAccountID
		}
	}

	// Validate and update default income account if provided
	if input.DefaultIncomeAccountID != nil {
		if *input.DefaultIncomeAccountID == 0 {
			// Clear the default income account
			settings.DefaultIncomeAccountID = nil
		} else {
			// Validate account exists
			if s.accountRepo != nil {
				exists, err := s.accountRepo.ExistsByID(userID, *input.DefaultIncomeAccountID)
				if err != nil {
					return nil, fmt.Errorf("failed to validate income account: %w", err)
				}
				if !exists {
					return nil, ErrDefaultAccountNotFound
				}
			}
			settings.DefaultIncomeAccountID = input.DefaultIncomeAccountID
		}
	}

	// Save to database
	if err := s.repo.Update(settings); err != nil {
		return nil, fmt.Errorf("failed to update settings: %w", err)
	}

	// Build response with account details
	response := &DefaultAccountsResponse{
		DefaultExpenseAccountID: settings.DefaultExpenseAccountID,
		DefaultIncomeAccountID:  settings.DefaultIncomeAccountID,
	}

	// Load account details if account repo is available
	if s.accountRepo != nil {
		if settings.DefaultExpenseAccountID != nil {
			account, err := s.accountRepo.GetByID(userID, *settings.DefaultExpenseAccountID)
			if err == nil {
				response.DefaultExpenseAccount = account
			}
		}
		if settings.DefaultIncomeAccountID != nil {
			account, err := s.accountRepo.GetByID(userID, *settings.DefaultIncomeAccountID)
			if err == nil {
				response.DefaultIncomeAccount = account
			}
		}
	}

	return response, nil
}

// ClearDefaultAccount clears the default account setting when an account is deleted
// This should be called when an account is deleted to maintain data consistency
// Feature: financial-core-upgrade
// Validates: Requirements 5.6
func (s *UserSettingsService) ClearDefaultAccount(userID uint, accountID uint) error {
	settings, err := s.repo.GetOrCreate(userID)
	if err != nil {
		return fmt.Errorf("failed to get settings: %w", err)
	}

	updated := false

	// Clear default expense account if it matches the deleted account
	if settings.DefaultExpenseAccountID != nil && *settings.DefaultExpenseAccountID == accountID {
		settings.DefaultExpenseAccountID = nil
		updated = true
	}

	// Clear default income account if it matches the deleted account
	if settings.DefaultIncomeAccountID != nil && *settings.DefaultIncomeAccountID == accountID {
		settings.DefaultIncomeAccountID = nil
		updated = true
	}

	// Only update if changes were made
	if updated {
		if err := s.repo.Update(settings); err != nil {
			return fmt.Errorf("failed to clear default account: %w", err)
		}
	}

	return nil
}

// GetDefaultAccountForType returns the default account ID for a given transaction type
// Feature: financial-core-upgrade
// Validates: Requirements 5.3, 5.4, 5.5
func (s *UserSettingsService) GetDefaultAccountForType(userID uint, transactionType string) (*uint, error) {
	settings, err := s.repo.GetOrCreate(userID)
	if err != nil {
		return nil, fmt.Errorf("failed to get settings: %w", err)
	}

	switch transactionType {
	case "expense":
		return settings.DefaultExpenseAccountID, nil
	case "income":
		return settings.DefaultIncomeAccountID, nil
	default:
		return nil, nil
	}
}