From b8f584407e0aef291b96d753c4a7355f3a45cb21 Mon Sep 17 00:00:00 2001
From: Andy Allan <git@gravitystorm.co.uk>
Date: Wed, 15 Oct 2025 18:10:06 +0100
Subject: [PATCH] Enable ActionMailer Previews

The previews run using the development database, which may or may not already contain
sufficient records (e.g. diary comments). So to avoid failures, we generate content
using factory bot, and to avoid filling your development database with duplicate data,
we run the previews inside a transaction.

If you manually create records in the database that collide with factory bot (e.g. users
with the same email pattern as the factory) then you'll need to update your manual records
to avoid collisions.
---
 CONFIGURE.md                                 |  4 ++++
 test/mailers/previews/user_mailer_preview.rb | 25 ++++++++++++++++++++
 2 files changed, 29 insertions(+)
 create mode 100644 test/mailers/previews/user_mailer_preview.rb

diff --git a/CONFIGURE.md b/CONFIGURE.md
index 84a7704e8..025b41132 100644
--- a/CONFIGURE.md
+++ b/CONFIGURE.md
@@ -189,6 +189,10 @@ Rails has its own log. To inspect the log during development:
 tail -f log/development.log
 ```
 
+### Email Previews
+
+We use [ActionMailer Previews](https://guides.rubyonrails.org/action_mailer_basics.html#previewing-and-testing-mailers) to generate previews of the emails sent by the application. Visit [http://localhost:3000/rails/mailers](http://localhost:3000/rails/mailers) to see the list of available previews.
+
 ### Maintaining Your Installation
 
 > [!TIP]
diff --git a/test/mailers/previews/user_mailer_preview.rb b/test/mailers/previews/user_mailer_preview.rb
new file mode 100644
index 000000000..54fb53b41
--- /dev/null
+++ b/test/mailers/previews/user_mailer_preview.rb
@@ -0,0 +1,25 @@
+# frozen_string_literal: true
+
+require "factory_bot_rails"
+
+class UserMailerPreview < ActionMailer::Preview
+  include FactoryBot::Syntax::Methods
+
+  # Wraps the preview in a transaction, so that no changes
+  # are persisted to the development db
+  def self.call(...)
+    preview = nil
+    ActiveRecord::Base.transaction do
+      preview = super(...)
+      raise ActiveRecord::Rollback
+    end
+    preview
+  end
+
+  def diary_comment_notification
+    recipient = create(:user, :languages => [I18n.locale])
+    diary_entry = create(:diary_entry)
+    diary_comment = create(:diary_comment, :diary_entry => diary_entry)
+    UserMailer.diary_comment_notification(diary_comment, recipient)
+  end
+end
-- 
2.39.5