refactor: centralize DTO decode/validation and skip duplicate validation

internal/handlers/common.go

@@ -15,6 +15,7 @@ import (
 	"goyco/internal/dto"
 	"goyco/internal/middleware"
 	"goyco/internal/services"
+	"goyco/internal/validation"
 
 	"github.com/go-chi/chi/v5"
 	"gorm.io/gorm"
@@ -272,13 +273,51 @@ func HandleServiceError(w http.ResponseWriter, err error, defaultMsg string, def
 	return false
 }
 
-func GetValidatedDTO[T any](r *http.Request) (*T, bool) {
+func GetValidatedDTO[T any](w http.ResponseWriter, r *http.Request) (*T, bool) {
 	dtoVal := middleware.GetValidatedDTOFromContext(r.Context())
-	if dtoVal == nil {
+	dtoTypeInContext := middleware.GetDTOTypeFromContext(r.Context())
+
+	var dto *T
+	needsValidation := false
+
+	if dtoVal != nil {
+		var ok bool
+		dto, ok = dtoVal.(*T)
+		if !ok {
 			return nil, false
 		}
-	dto, ok := dtoVal.(*T)
-	return dto, ok
+		if dtoTypeInContext == nil {
+			needsValidation = true
+		}
+	} else {
+		var decoded T
+		if err := json.NewDecoder(r.Body).Decode(&decoded); err != nil {
+			SendErrorResponse(w, "Invalid JSON", http.StatusBadRequest)
+			return nil, false
+		}
+		dto = &decoded
+		needsValidation = true
+	}
+
+	if needsValidation {
+		if err := validation.ValidateStruct(dto); err != nil {
+			var errorMessages []string
+			if structErr, ok := err.(*validation.StructValidationError); ok {
+				errorMessages = make([]string, len(structErr.Errors))
+				for i, fieldError := range structErr.Errors {
+					errorMessages[i] = fieldError.Message
+				}
+			} else {
+				errorMessages = []string{err.Error()}
+			}
+
+			errorMsg := strings.Join(errorMessages, "; ")
+			SendErrorResponse(w, errorMsg, http.StatusBadRequest)
+			return nil, false
+		}
+	}
+
+	return dto, true
 }
 
 func WithValidation[T any](validationMiddleware func(http.Handler) http.Handler, handler http.HandlerFunc) http.HandlerFunc {