Add public preview links for drafts

Lets editors share a draft with people outside the admin system, via a
random per-page token rather than an enumerable id - /preview/<token>.
shared_previews#show is intentionally unauthenticated. Redirects to the
real public URL once the page is published. Surfaced on nodes#show
(Admin Preview + Public Preview, next to Public Link) as generate/revoke
buttons.

1 files changed, 13 insertions, 0 deletions

diff --git a/app/controllers/shared_previews_controller.rb b/app/controllers/shared_previews_controller.rb
new file mode 100644
index 0000000..a8a540f
--- /dev/null
+++ b/app/controllers/shared_previews_controller.rb
@@ -0,0 +1,13 @@
+class SharedPreviewsController < ApplicationController
+  def show
+    @page = Page.find_by!(preview_token: params[:token])
+
+    if @page.node && @page.node.head_id == @page.id
+      redirect_to node_path(@page.node)
+      return
+    end
+
+    response.headers['X-Robots-Tag'] = 'noindex'
+    render template: @page.valid_template, layout: "application"
+  end
+end