Prevent signup from UI when a user already exists

handler/auth.go

@@ -54,6 +54,12 @@ type AuthHandler struct {
 }
 
 func (h *AuthHandler) ServeSignup(w http.ResponseWriter, r *http.Request) {
+	count, err := h.Store.UserCount()
+	if err == nil && count > 0 {
+		http.Redirect(w, r, "/signin", http.StatusSeeOther)
+		return
+	}
+
 	if r.Method == http.MethodGet {
 		h.Tpl.Render(w, "signup", nil)
 		return
@@ -91,9 +97,14 @@ func (h *AuthHandler) ServeSignup(w http.ResponseWriter, r *http.Request) {
 	}
 }
 
+func (h *AuthHandler) hasUsers() bool {
+	count, err := h.Store.UserCount()
+	return err == nil && count > 0
+}
+
 func (h *AuthHandler) ServeSignin(w http.ResponseWriter, r *http.Request) {
 	if r.Method == http.MethodGet {
-		h.Tpl.Render(w, "signin", nil)
+		h.Tpl.Render(w, "signin", map[string]any{"HasUser": h.hasUsers()})
 		return
 	}
 
@@ -103,12 +114,12 @@ func (h *AuthHandler) ServeSignin(w http.ResponseWriter, r *http.Request) {
 
 		user, err := h.Store.UserByEmail(email)
 		if err != nil {
-			h.Tpl.Render(w, "signin", map[string]string{"Error": "Invalid email or password."})
+			h.Tpl.Render(w, "signin", map[string]any{"Error": "Invalid email or password.", "HasUser": h.hasUsers()})
 			return
 		}
 
 		if err := bcrypt.CompareHashAndPassword([]byte(user.PasswordHash), []byte(password)); err != nil {
-			h.Tpl.Render(w, "signin", map[string]string{"Error": "Invalid email or password."})
+			h.Tpl.Render(w, "signin", map[string]any{"Error": "Invalid email or password.", "HasUser": h.hasUsers()})
 			return
 		}