From 0f140fe15852b829d22864a2f7664440204ac723 Mon Sep 17 00:00:00 2001
From: David Heinemeier Hansson <david@loudthinking.com>
Date: Tue, 18 Sep 2018 16:42:38 -0700
Subject: Add callbacks

---
 lib/action_mailroom/mailbox.rb           |  9 +++++++--
 lib/action_mailroom/mailbox/callbacks.rb | 28 ++++++++++++++++++++++++++++
 test/unit/mailbox/callbacks_test.rb      | 25 +++++++++++++++++++++++++
 3 files changed, 60 insertions(+), 2 deletions(-)
 create mode 100644 lib/action_mailroom/mailbox/callbacks.rb
 create mode 100644 test/unit/mailbox/callbacks_test.rb

diff --git a/lib/action_mailroom/mailbox.rb b/lib/action_mailroom/mailbox.rb
index 44dcd691b1..0d03f4be6b 100644
--- a/lib/action_mailroom/mailbox.rb
+++ b/lib/action_mailroom/mailbox.rb
@@ -1,7 +1,8 @@
 require "active_support/rescuable"
+require "action_mailroom/mailbox/callbacks"
 
 class ActionMailroom::Mailbox
-  include ActiveSupport::Rescuable
+  include ActiveSupport::Rescuable, Callbacks
 
   class << self
     def receive(inbound_email)
@@ -22,7 +23,11 @@ class ActionMailroom::Mailbox
 
   def perform_processing
     inbound_email.processing!
-    process
+
+    run_callbacks :process do
+      process
+    end
+
     inbound_email.delivered!
   rescue => exception
     inbound_email.failed!
diff --git a/lib/action_mailroom/mailbox/callbacks.rb b/lib/action_mailroom/mailbox/callbacks.rb
new file mode 100644
index 0000000000..ae5a461d8f
--- /dev/null
+++ b/lib/action_mailroom/mailbox/callbacks.rb
@@ -0,0 +1,28 @@
+require "active_support/callbacks"
+
+module ActionMailroom
+  class Mailbox
+    module Callbacks
+      extend  ActiveSupport::Concern
+      include ActiveSupport::Callbacks
+
+      included do
+        define_callbacks :process
+      end
+
+      module ClassMethods
+        def before_processing(*methods, &block)
+          set_callback(:process, :before, *methods, &block)
+        end
+
+        def after_processing(*methods, &block)
+          set_callback(:process, :after, *methods, &block)
+        end
+
+        def around_processing(*methods, &block)
+          set_callback(:process, :around, *methods, &block)
+        end
+      end
+    end
+  end
+end
diff --git a/test/unit/mailbox/callbacks_test.rb b/test/unit/mailbox/callbacks_test.rb
new file mode 100644
index 0000000000..ada6410876
--- /dev/null
+++ b/test/unit/mailbox/callbacks_test.rb
@@ -0,0 +1,25 @@
+require_relative '../../test_helper'
+
+class CallbackMailbox < ActionMailroom::Mailbox
+  before_processing { $before_processing = "Ran that!" }
+  after_processing  { $after_processing = "Ran that too!" }
+  around_processing ->(r, block) { block.call; $around_processing = "Ran that as well!" }
+
+  def process
+    $processed = mail.subject
+  end
+end
+
+class ActionMailroom::Mailbox::CallbacksTest < ActiveSupport::TestCase
+  setup do
+    $before_processing = $after_processing = $around_processing = $processed = false
+    @inbound_email = create_inbound_email("welcome.eml")
+  end
+
+  test "all callback types" do
+    CallbackMailbox.receive @inbound_email
+    assert_equal "Ran that!", $before_processing
+    assert_equal "Ran that too!", $after_processing
+    assert_equal "Ran that as well!", $around_processing
+  end
+end
-- 
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