FEATURE: Before consolidation callbacks. (#15428)

You can add callbacks that get called before updating an already consolidated notification or creating a consolidated one.

Instances of this rule can add callbacks to access the old notifications about to be destroyed or the consolidated one and add additional data inside the data hash versus having to execute extra queries when adding this logic inside the `set_mutations` block.

spec/services/notifications/consolidate_notifications_spec.rb

@@ -0,0 +1,60 @@
+# frozen_string_literal: true
+
+require 'rails_helper'
+
+describe Notifications::ConsolidateNotifications do
+  describe '#before_consolidation_callbacks' do
+    fab!(:user) { Fabricate(:user) }
+    let(:rule) do
+      described_class.new(
+        from: Notification.types[:liked],
+        to: Notification.types[:liked],
+        consolidation_window: 10.minutes,
+        consolidated_query_blk: Proc.new do |notifications|
+          notifications.where("(data::json ->> 'consolidated')::bool")
+        end,
+        threshold: 1
+      ).set_mutations(set_data_blk: Proc.new { |n| n.data_hash.merge(consolidated: true) })
+    end
+
+    it 'applies a callback when consolidating a notification' do
+      rule.before_consolidation_callbacks(
+        before_consolidation_blk: Proc.new do |_, data|
+          data[:consolidation_callback_called] = true
+        end
+      )
+
+      rule.consolidate_or_save!(build_like_notification)
+      rule.consolidate_or_save!(build_like_notification)
+
+      consolidated_notification = Notification.where(user: user).last
+
+      expect(consolidated_notification.data_hash[:consolidation_callback_called]).to eq(true)
+    end
+
+    it 'applies a callback when updating a consolidated notification' do
+      rule.before_consolidation_callbacks(
+        before_update_blk: Proc.new do |_, data|
+          data[:update_callback_called] = true
+        end
+      )
+
+      rule.consolidate_or_save!(build_like_notification)
+      rule.consolidate_or_save!(build_like_notification)
+
+      consolidated_notification = Notification.where(user: user).last
+
+      expect(consolidated_notification.data_hash[:update_callback_called]).to be_nil
+
+      rule.consolidate_or_save!(build_like_notification)
+
+      consolidated_notification = Notification.where(user: user).last
+
+      expect(consolidated_notification.data_hash[:update_callback_called]).to eq(true)
+    end
+
+    def build_like_notification
+      Fabricate.build(:notification, user: user, notification_type: Notification.types[:liked], data: {}.to_json)
+    end
+  end
+end