Implements API validator and uses it in user endpoint

internal/api/user.go

@@ -27,6 +27,12 @@ func (h *Handler) createUser(c *fiber.Ctx) error {
 		return defaultUserError
 	}
 
+	validationErr := ValidateModel(user)
+
+	if validationErr != nil {
+		return validationErr
+	}
+
 	_, insertErr := h.db.Exec("INSERT INTO user (id, first_name, email) VALUES (?, ?, ?)", user.ID, user.FirstName, user.Email)
 
 	if insertErr != nil {

internal/api/validator.go

@@ -0,0 +1,36 @@
+package api
+
+import (
+	"fmt"
+	"freed/internal/model"
+	"strings"
+
+	"github.com/go-playground/validator/v10"
+	"github.com/gofiber/fiber/v2"
+)
+
+type ModelConstraint interface {
+	*model.User // | add other models here
+}
+
+type ValidationError struct {
+	FailedField string
+	Tag         string
+	Value       string
+}
+
+func ValidateModel[T ModelConstraint](s T) *fiber.Error {
+	var errorMessages []string
+	validate := validator.New()
+	err := validate.Struct(s)
+
+	if err != nil {
+		for _, err := range err.(validator.ValidationErrors) {
+			err := fmt.Sprintf("Field %s is invalid, reason: %s", err.StructNamespace(), err.Tag())
+
+			errorMessages = append(errorMessages, err)
+		}
+	}
+
+	return fiber.NewError(fiber.StatusBadRequest, strings.Join(errorMessages, ". "))
+}