Properly handle failed captchas after XHR post (#85)

* handle form posts and xhr posts differently on captcha failure

* formatting

assets/js/ujs.js

@@ -2,7 +2,8 @@ import { $$, makeEl, findFirstTextNode } from './utils/dom';
 import { fire, delegate, leftClick } from './utils/events';
 
 const headers = () => ({
-  'x-csrf-token': window.booru.csrfToken
+  'x-csrf-token': window.booru.csrfToken,
+  'x-requested-with': 'XMLHttpRequest'
 });
 
 function confirm(event, target) {
@@ -56,9 +57,13 @@ function formRemote(event, target) {
     method: (target.dataset.method || target.method || 'POST').toUpperCase(),
     headers: headers(),
     body: new FormData(target)
-  }).then(response =>
+  }).then(response => {
+    if (response && response.status == 300) {
+      window.location.reload(true);
+      return;
+    }
     fire(target, 'fetchcomplete', response)
-  );
+  });
 }
 
 function formReset(event, target) {

lib/philomena_web/plugs/captcha_plug.ex

@@ -1,7 +1,7 @@
 defmodule PhilomenaWeb.CaptchaPlug do
   alias Philomena.Captcha
-  alias Phoenix.Controller
-  alias Plug.Conn
+  import Plug.Conn
+  import Phoenix.Controller
 
   def init([]), do: false
 
@@ -19,14 +19,31 @@ defmodule PhilomenaWeb.CaptchaPlug do
 
       false ->
         conn
-        |> Controller.put_flash(
+        |> put_flash(
           :error,
           "There was an error verifying you're not a robot. Please try again."
         )
-        |> Controller.redirect(external: conn.assigns.referrer)
-        |> Conn.halt()
+        |> do_failure_response(ajax?(conn))
+        |> halt()
     end
   end
 
   defp maybe_check_captcha(conn, _user), do: conn
+
+  defp do_failure_response(conn, true) do
+    conn
+    |> put_status(:multiple_choices)
+    |> text("")
+  end
+
+  defp do_failure_response(conn, _false) do
+    redirect(conn, external: conn.assigns.referrer)
+  end
+
+  def ajax?(conn) do
+    case get_req_header(conn, "x-requested-with") do
+      [value] -> String.downcase(value) == "xmlhttprequest"
+      _ -> false
+    end
+  end
 end