From 1541305022b679b4610a62ad14161c31da0fc993 Mon Sep 17 00:00:00 2001
From: tamsin johnson <tomjohnson@ucsb.edu>
Date: Fri, 2 Feb 2024 21:24:04 -0800
Subject: [PATCH] lets-go:8.5 validation helpers

---
 snippetbox/cmd/web/handlers.go             | 25 ++++--------
 snippetbox/internal/validator/validator.go | 47 ++++++++++++++++++++++
 2 files changed, 54 insertions(+), 18 deletions(-)
 create mode 100644 snippetbox/internal/validator/validator.go

diff --git a/snippetbox/cmd/web/handlers.go b/snippetbox/cmd/web/handlers.go
index 5b0039d..6e5176d 100644
--- a/snippetbox/cmd/web/handlers.go
+++ b/snippetbox/cmd/web/handlers.go
@@ -5,11 +5,10 @@ import (
 	"fmt"
 	"net/http"
 	"strconv"
-	"strings"
-	"unicode/utf8"
 
 	"github.com/julienschmidt/httprouter"
 	"snippetbox.chaosfem.tw/internal/models"
+	"snippetbox.chaosfem.tw/internal/validator"
 )
 
 // home ...
@@ -67,7 +66,7 @@ type snippetCreateForm struct {
 	Title       string
 	Content     string
 	Expires     int
-	FieldErrors map[string]string
+	validator.Validator
 }
 
 // snippetCreatePost ...
@@ -88,24 +87,14 @@ func (app *application) snippetCreatePost(w http.ResponseWriter, r *http.Request
 		Title:       r.PostForm.Get("title"),
 		Content:     r.PostForm.Get("content"),
 		Expires:     expires,
-		FieldErrors: map[string]string{},
 	}
 
-	if strings.TrimSpace(form.Title) == "" {
-		form.FieldErrors["title"] = "This field cannot be blank"
-	} else if utf8.RuneCountInString(form.Title) > 100 {
-		form.FieldErrors["title"] = "This field cannot contain more than 100 characters"
-	}
+	form.CheckField(validator.NotBlank(form.Title), "title", "This field cannot be blank")
+	form.CheckField(validator.MaxChars(form.Title, 100), "title", "This field cannot be more than 100 characters long")
+	form.CheckField(validator.NotBlank(form.Content), "content", "This field cannot be blank")
+	form.CheckField(validator.PermittedValue(form.Expires, 1, 7, 365), "expires", "This field must equal 1, 7 or 365")
 
-	if strings.TrimSpace(form.Content) == "" {
-		form.FieldErrors["content"] = "This field cannot be blank"
-	}
-
-	if form.Expires != 1 && form.Expires != 7 && form.Expires != 365 {
-		form.FieldErrors["expires"] = "This field must equal 1, 7 or 365"
-	}
-
-	if len(form.FieldErrors) > 0 {
+	if !form.Valid() {
 		data := app.newTemplateData(r)
 		data.Form = form
 		app.render(w, r, http.StatusUnprocessableEntity, "create.tmpl", data)
diff --git a/snippetbox/internal/validator/validator.go b/snippetbox/internal/validator/validator.go
new file mode 100644
index 0000000..aebe156
--- /dev/null
+++ b/snippetbox/internal/validator/validator.go
@@ -0,0 +1,47 @@
+package validator
+
+import (
+	"slices"
+	"strings"
+	"unicode/utf8"
+)
+
+type Validator struct {
+	FieldErrors map[string]string
+}
+
+// Valid() ...
+func (v *Validator) Valid() bool {
+	return len(v.FieldErrors) == 0
+}
+
+// AddFieldError ...
+func (v *Validator) AddFieldError(key, message string) {
+	if v.FieldErrors == nil {
+		v.FieldErrors = make(map[string]string)
+	}
+
+	if _, exists := v.FieldErrors[key]; !exists {
+		v.FieldErrors[key] = message
+	}
+}
+
+// CheckField ...
+func (v *Validator) CheckField(ok bool, key, message string)  {
+	if !ok {
+		v.AddFieldError(key, message)
+	}
+}
+
+func NotBlank(value string) bool {
+	return strings.TrimSpace(value) != ""
+}
+
+func MaxChars(value string, n int) bool {
+	return utf8.RuneCountInString(value) <= n
+}
+
+// PermittedValue[T comparable] ...
+func PermittedValue[T comparable](value T, permittedValues ...T) bool {
+	return slices.Contains(permittedValues, value)
+}