package adminstore

import (
	"context"
	"errors"
	"fmt"
	"strings"

	"github.com/jackc/pgx/v5"
)

// Brand-management errors, mapped to client statuses by the handler.
var (
	// ErrDuplicateBrand is returned when a brand name already exists.
	ErrDuplicateBrand = errors.New("duplicate brand name")
	// ErrBrandInUse blocks deleting a brand still referenced by products.
	ErrBrandInUse = errors.New("brand in use")
	// ErrInvalidMerge is returned when a merge target is missing or equal to
	// the source.
	ErrInvalidMerge = errors.New("invalid merge target")
)

// CreateBrand inserts a new brand. Names are unique by normalized form.
func (s *Store) CreateBrand(ctx context.Context, actor, name string) (*Brand, error) {
	name = strings.TrimSpace(name)
	if name == "" {
		return nil, errors.New("name required")
	}
	var b Brand
	err := s.pool.QueryRow(ctx,
		`INSERT INTO brand (name, normalized_name) VALUES ($1, $2) RETURNING id, name, 0`,
		name, normBrand(name)).Scan(&b.ID, &b.Name, &b.ProductCount)
	if isUniqueViolation(err) {
		return nil, ErrDuplicateBrand
	}
	if err != nil {
		return nil, err
	}
	_ = s.writeAudit(ctx, actor, "create", "brand", &b.ID, []string{"name"}, nil, b)
	return &b, nil
}

// UpdateBrand renames a brand, keeping the normalized name in sync.
func (s *Store) UpdateBrand(ctx context.Context, id, actor, name string) (*Brand, error) {
	name = strings.TrimSpace(name)
	if name == "" {
		return nil, errors.New("name required")
	}
	ct, err := s.pool.Exec(ctx,
		"UPDATE brand SET name = $1, normalized_name = $2 WHERE id = $3",
		name, normBrand(name), id)
	if isUniqueViolation(err) {
		return nil, ErrDuplicateBrand
	}
	if err != nil {
		return nil, err
	}
	if ct.RowsAffected() == 0 {
		return nil, ErrNotFound
	}
	out, err := s.getBrand(ctx, id)
	if err != nil {
		return nil, err
	}
	_ = s.writeAudit(ctx, actor, "update", "brand", &id, []string{"name"}, nil, out)
	return out, nil
}

// MergeBrands reassigns every product of src to dst, then deletes src. Useful
// for collapsing duplicate brands (e.g. "可口可乐" and "Coca-Cola").
func (s *Store) MergeBrands(ctx context.Context, srcID, dstID, actor string) (*Brand, error) {
	if srcID == dstID {
		return nil, ErrInvalidMerge
	}
	tx, err := s.pool.Begin(ctx)
	if err != nil {
		return nil, err
	}
	defer tx.Rollback(ctx)

	var dstName string
	err = tx.QueryRow(ctx, "SELECT name FROM brand WHERE id = $1", dstID).Scan(&dstName)
	if errors.Is(err, pgx.ErrNoRows) {
		return nil, ErrInvalidMerge
	}
	if err != nil {
		return nil, err
	}
	var srcName string
	err = tx.QueryRow(ctx, "SELECT name FROM brand WHERE id = $1", srcID).Scan(&srcName)
	if errors.Is(err, pgx.ErrNoRows) {
		return nil, ErrNotFound
	}
	if err != nil {
		return nil, err
	}

	if _, err := tx.Exec(ctx, "UPDATE product SET brand_id = $1 WHERE brand_id = $2", dstID, srcID); err != nil {
		return nil, err
	}
	if _, err := tx.Exec(ctx, "DELETE FROM brand WHERE id = $1", srcID); err != nil {
		return nil, err
	}
	if err := tx.Commit(ctx); err != nil {
		return nil, err
	}

	out, err := s.getBrand(ctx, dstID)
	if err != nil {
		return nil, err
	}
	_ = s.writeAudit(ctx, actor, "merge", "brand", &srcID, []string{"name"},
		map[string]string{"name": srcName},
		map[string]string{"merged_into": dstName, "merged_into_id": dstID})
	return out, nil
}

// DeleteBrand removes a brand not referenced by any product.
func (s *Store) DeleteBrand(ctx context.Context, id, actor string) error {
	before, err := s.getBrand(ctx, id)
	if err != nil {
		return err
	}
	if before.ProductCount > 0 {
		return fmt.Errorf("%w: %d products", ErrBrandInUse, before.ProductCount)
	}
	ct, err := s.pool.Exec(ctx, "DELETE FROM brand WHERE id = $1", id)
	if err != nil {
		if isForeignKeyViolation(err) {
			return ErrBrandInUse
		}
		return err
	}
	if ct.RowsAffected() == 0 {
		return ErrNotFound
	}
	_ = s.writeAudit(ctx, actor, "delete", "brand", &id, []string{"name"}, before, nil)
	return nil
}

func (s *Store) getBrand(ctx context.Context, id string) (*Brand, error) {
	var b Brand
	err := s.pool.QueryRow(ctx, `
SELECT b.id, b.name,
       (SELECT count(*) FROM product p WHERE p.brand_id = b.id)
FROM brand b WHERE b.id = $1`, id).Scan(&b.ID, &b.Name, &b.ProductCount)
	if errors.Is(err, pgx.ErrNoRows) {
		return nil, ErrNotFound
	}
	if err != nil {
		return nil, err
	}
	return &b, nil
}