feat: add data validation and structured logging

internal/utils/validator.go

@@ -0,0 +1,47 @@
+package utils
+
+import (
+	"fmt"
+	"strings"
+
+	"github.com/go-playground/validator/v10"
+)
+
+var validate *validator.Validate
+
+func init() {
+	validate = validator.New()
+}
+
+// ValidationErrorResponse represents the structure of validation errors returned to the client
+type ValidationErrorResponse struct {
+	Errors map[string]string `json:"errors"`
+}
+
+// ValidateStruct validates a struct based on its tags using go-playground/validator
+func ValidateStruct(s interface{}) *ValidationErrorResponse {
+	err := validate.Struct(s)
+	if err != nil {
+		var errorsMap = make(map[string]string)
+		for _, err := range err.(validator.ValidationErrors) {
+			// Simpler error messages for now. Can be enhanced with universal-translator.
+			fieldName := strings.ToLower(err.Field())
+			switch err.Tag() {
+			case "required":
+				errorsMap[fieldName] = fmt.Sprintf("Field '%s' is required", fieldName)
+			case "email":
+				errorsMap[fieldName] = fmt.Sprintf("Field '%s' must be a valid email", fieldName)
+			case "min":
+				errorsMap[fieldName] = fmt.Sprintf("Field '%s' must be at least %s characters long", fieldName, err.Param())
+			case "max":
+				errorsMap[fieldName] = fmt.Sprintf("Field '%s' must be at most %s characters long", fieldName, err.Param())
+			case "alphanum":
+				errorsMap[fieldName] = fmt.Sprintf("Field '%s' must contain only alphanumeric characters", fieldName)
+			default:
+				errorsMap[fieldName] = fmt.Sprintf("Field '%s' failed validation on '%s' tag", fieldName, err.Tag())
+			}
+		}
+		return &ValidationErrorResponse{Errors: errorsMap}
+	}
+	return nil
+}