Enhance Customer Module with Validation and Username Handling

- Introduced a new ValidationService for customer operations to ensure valid username formats.
- Updated customer service and handler to utilize the new validation service, enhancing input validation during registration and updates.
- Modified CreateCustomerForm and UpdateCustomerForm to enforce username validation rules.
- Adjusted repository indexing to improve search efficiency by refining the text index for customer data.
- Ensured consistent handling of usernames across the customer module, improving overall data integrity and user experience.

internal/customer/validation.go

@@ -0,0 +1,41 @@
+package customer
+
+import (
+	"regexp"
+
+	"github.com/asaskevich/govalidator"
+)
+
+// ValidationService defines validation methods for customer operations
+type ValidationService interface {
+	IsValidUsername(username string) bool
+}
+
+// validationService implements the ValidationService interface
+type validationService struct {
+	usernameRegex *regexp.Regexp
+}
+
+// NewValidationService creates a new validation service
+func NewValidationService() ValidationService {
+	// Compile the username regex pattern
+	usernameRegex := regexp.MustCompile(`^[a-zA-Z0-9](?:[a-zA-Z0-9._]*[a-zA-Z0-9])?$`)
+
+	// Register custom validator with govalidator
+	govalidator.CustomTypeTagMap.Set("username", govalidator.CustomTypeValidator(func(i interface{}, o interface{}) bool {
+		username, ok := i.(string)
+		if !ok {
+			return false
+		}
+		return usernameRegex.MatchString(username)
+	}))
+
+	return &validationService{
+		usernameRegex: usernameRegex,
+	}
+}
+
+// IsValidUsername checks if a username matches the required pattern
+func (v *validationService) IsValidUsername(username string) bool {
+	return v.usernameRegex.MatchString(username)
+}