Fix shared preview links breaking after a second publish

A token's page could stop being node.head_id (superseded by a newer
draft) while still being published_at.present? - the old check only
compared against the current head, so a superseded page fell through
to direct rendering instead of redirecting, serving a stale frozen
snapshot indefinitely instead of the current live content.

Also handles scheduled publishing correctly: a page can be head_id but
not yet public? (published_at in the future) - that case must still
render directly, not redirect into a 404 on the not-yet-live public
URL.

2 files changed, 41 insertions, 3 deletions

diff --git a/app/controllers/shared_previews_controller.rb b/app/controllers/shared_previews_controller.rb
index a8a540f..d482466 100644
--- a/app/controllers/shared_previews_controller.rb
+++ b/app/controllers/shared_previews_controller.rb
@@ -1,9 +1,14 @@
 class SharedPreviewsController < ApplicationController
   def show
     @page = Page.find_by!(preview_token: params[:token])
+    node  = @page.node
 
-    if @page.node && @page.node.head_id == @page.id
-      redirect_to node_path(@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+    superseded       = was_published && node && node.head_id != @page.id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+    if superseded || currently_public
+      redirect_to node_path(node)
       return
     end
 
diff --git a/test/models/page_test.rb b/test/models/page_test.rb
index afba8b5..ad2742f 100644
--- a/test/models/page_test.rb
+++ b/test/models/page_test.rb
@@ -142,5 +142,38 @@ class PageTest < ActiveSupport::TestCase
     update        = updates2009.children.create!( :slug => "my-first-update" )
     assert_equal "update", update.draft.template_name
   end
-  
+
+  test "a page scheduled for future publication is not yet public even after being published" do
+    node = Node.root.children.create!(slug: "preview-scheduled-test")
+    draft = node.find_or_create_draft(@user1)
+    draft.title = "Scheduled test"
+    draft.published_at = 1.day.from_now
+    draft.save!
+    token = draft.ensure_preview_token!
+
+    node.publish_draft!
+    page = Page.find_by(preview_token: token)
+
+    assert_equal page.id, page.node.head_id
+    assert_not page.public?
+  end
+
+  test "a superseded page is no longer the head, even though it was once published" do
+    node = Node.root.children.create!(slug: "preview-superseded-test")
+    first_draft = node.find_or_create_draft(@user1)
+    first_draft.title = "First version"
+    first_draft.save!
+    first_token = first_draft.ensure_preview_token!
+    node.publish_draft!
+
+    second_draft = node.find_or_create_draft(@user1)
+    second_draft.title = "Second version"
+    second_draft.save!
+    node.publish_draft!
+
+    first_page = Page.find_by(preview_token: first_token)
+
+    assert_not_equal first_page.id, first_page.node.head_id
+    assert first_page.published_at.present?
+  end
 end