Add BE validator

cmd/api/handlers-api.go

@@ -9,6 +9,7 @@ import (
 	"myapp/internal/cards/encryption"
 	"myapp/internal/models"
 	"myapp/internal/urlsigner"
+	"myapp/internal/validator"
 	"net/http"
 	"strconv"
 	"strings"
@@ -124,6 +125,14 @@ func (app *application) CreateCustomerAndSubscribeToPlan(w http.ResponseWriter,
 		return
 	}
 
+	// validate data
+	v := validator.New()
+	v.Check(len(data.FirstName) > 1, "first_name", "must be at least 2 characters")
+	if !v.Valid() {
+		app.failedValidation(w, r, v.Errors)
+		return
+	}
+
 	app.infoLog.Println(data.Email, data.LastFour, data.PaymentMethod, data.Plan)
 
 	card := cards.Card{

cmd/api/helpers.go

@@ -95,3 +95,20 @@ func (app *application) passwordMatches(hash, password string) (bool, error) {
 
 	return true, nil
 }
+
+func (app *application) failedValidation(
+	w http.ResponseWriter,
+	r *http.Request,
+	errors map[string]string,
+) {
+	var payload struct {
+		OK      bool              `json:"ok"`
+		Message string            `json:"message"`
+		Errors  map[string]string `json:"errors"`
+	}
+
+	payload.OK = false
+	payload.Message = "failed validation"
+	payload.Errors = errors
+	app.writeJSON(w, http.StatusUnprocessableEntity, payload)
+}