Fix shared preview redirecting to admin for an ordinary new draft

superseded/currently_public used published_at presence as a proxy
for page-row relevance, but published_at is carried forward onto
every new draft descended from previously-published content
(Page#clone_attributes_from, Node#save_draft!) -- so it read true
for any draft on an already-published node, whether or not that
specific draft had ever gone live itself. Compare draft_id/head_id
identity directly instead; no timestamp involved. A stale
(superseded) link now redirects to the live public page rather than
an admin URL an anonymous holder can't reach anyway.

1 files changed, 10 insertions, 6 deletions

diff --git a/app/controllers/shared_previews_controller.rb b/app/controllers/shared_previews_controller.rb
index d482466..f6fb45a 100644
--- a/app/controllers/shared_previews_controller.rb
+++ b/app/controllers/shared_previews_controller.rb
@@ -3,13 +3,17 @@ class SharedPreviewsController < ApplicationController
     @page = Page.find_by!(preview_token: params[:token])
     node  = @page.node
 
-    was_published    = @page.published_at.present?
-    superseded       = was_published && node && node.head_id != @page.id
-    currently_public = was_published && node && node.head_id == @page.id && @page.public?
+    if node
+      is_head  = node.head_id  == @page.id
+      is_draft = node.draft_id == @page.id
 
-    if superseded || currently_public
-      redirect_to node_path(node)
-      return
+      currently_public = is_head && @page.public?
+      superseded        = !is_head && !is_draft
+
+      if superseded || currently_public
+        redirect_to @page.public_link
+        return
+      end
     end
 
     response.headers['X-Robots-Tag'] = 'noindex'