feat: create specific price system and adapt product queries

app/utils/responseErrors/responseErrors.go

@@ -62,6 +62,12 @@ var (
 	ErrUserHasNoSuchCart                 = errors.New("user does not have cart with given id")
 	ErrProductOrItsVariationDoesNotExist = errors.New("product or its variation with given ids does not exist")
 
+	// Typed errors for price reduction handler
+	ErrInvalidReductionType  = errors.New("invalid reduction type: must be 'amount' or 'percentage'")
+	ErrPercentageRequired    = errors.New("percentage_reduction required when reduction_type is percentage")
+	ErrPriceRequired         = errors.New("price required when reduction_type is amount")
+	ErrSpecificPriceNotFound = errors.New("price reduction not found")
+
 	// Typed errors for data parsing
 	ErrJSONBody = errors.New("invalid JSON body")
 )
@@ -171,6 +177,15 @@ func GetErrorCode(c fiber.Ctx, err error) string {
 	case errors.Is(err, ErrProductOrItsVariationDoesNotExist):
 		return i18n.T_(c, "error.product_or_its_variation_does_not_exist")
 
+	case errors.Is(err, ErrInvalidReductionType):
+		return i18n.T_(c, "error.invalid_reduction_type")
+	case errors.Is(err, ErrPercentageRequired):
+		return i18n.T_(c, "error.percentage_required")
+	case errors.Is(err, ErrPriceRequired):
+		return i18n.T_(c, "error.price_required")
+	case errors.Is(err, ErrSpecificPriceNotFound):
+		return i18n.T_(c, "error.price_reduction_not_found")
+
 	case errors.Is(err, ErrJSONBody):
 		return i18n.T_(c, "error.err_json_body")
 
@@ -219,8 +234,13 @@ func GetErrorStatus(err error) int {
 		errors.Is(err, ErrMaxAmtOfCartsReached),
 		errors.Is(err, ErrUserHasNoSuchCart),
 		errors.Is(err, ErrProductOrItsVariationDoesNotExist),
+		errors.Is(err, ErrInvalidReductionType),
+		errors.Is(err, ErrPercentageRequired),
+		errors.Is(err, ErrPriceRequired),
 		errors.Is(err, ErrJSONBody):
 		return fiber.StatusBadRequest
+	case errors.Is(err, ErrSpecificPriceNotFound):
+		return fiber.StatusNotFound
 	case errors.Is(err, ErrEmailExists):
 		return fiber.StatusConflict
 	case errors.Is(err, ErrAIResponseFail),