adding a warning upon 'creating' a new document on an existing page

Summary: don't remember what I changed except for add that intermediate dialog

Test Plan:
{F35155}

Ugly, ain't it?

you can edit instead, or admit that it was a mistake to take on Phriction's existing documents

Reviewers: epriestley, chad, btrahan

Reviewed By: epriestley

CC: aran, Korvin

Maniphest Tasks: T2686

Differential Revision: https://secure.phabricator.com/D5295

src/applications/phriction/controller/PhrictionNewController.php

@@ -12,9 +12,32 @@ final class PhrictionNewController extends PhrictionController {
     $slug    = PhabricatorSlug::normalize($request->getStr('slug'));
 
     if ($request->isFormPost()) {
-      $uri  = '/phriction/edit/?slug='.$slug;
-      return id(new AphrontRedirectResponse())
-        ->setURI($uri);
+      $document = id(new PhrictionDocument())->loadOneWhere(
+        'slug = %s',
+        $slug);
+      $prompt = $request->getStr('prompt', 'no');
+      $document_exists = $document && $document->getStatus() ==
+        PhrictionDocumentStatus::STATUS_EXISTS;
+
+      if ($document_exists && $prompt == 'no') {
+        $dialog = new AphrontDialogView();
+        $dialog->setSubmitURI('/phriction/new/')
+          ->setTitle(pht('Edit Existing Document?'))
+          ->setUser($user)
+          ->appendChild(pht(
+            'The document %s already exists. Do you want to edit it instead?',
+            hsprintf('<tt>%s</tt>', $slug)))
+          ->addHiddenInput('slug', $slug)
+          ->addHiddenInput('prompt', 'yes')
+          ->addCancelButton('/w/')
+          ->addSubmitButton(pht('Edit Document'));
+
+        return id(new AphrontDialogResponse())->setDialog($dialog);
+      } else {
+        $uri  = '/phriction/edit/?slug='.$slug;
+        return id(new AphrontRedirectResponse())
+          ->setURI($uri);
+      }
     }
 
     if ($slug == '/') {