feat: Add support for template variables in messages content (#6215)

Fixes: #6078

Co-authored-by: Sojan <sojan@pepalo.com>

app/models/concerns/liquidable.rb

@@ -0,0 +1,36 @@
+module Liquidable
+  extend ActiveSupport::Concern
+
+  included do
+    acts_as_taggable_on :labels
+    before_create :process_liquid_in_content
+  end
+
+  private
+
+  def message_drops
+    {
+      'contact' => ContactDrop.new(conversation.contact),
+      'agent' => UserDrop.new(sender),
+      'conversation' => ConversationDrop.new(conversation),
+      'inbox' => InboxDrop.new(inbox)
+    }
+  end
+
+  def liquid_processable_message?
+    content.present? && message_type == 'outgoing'
+  end
+
+  def process_liquid_in_content
+    return unless liquid_processable_message?
+
+    template = Liquid::Template.parse(modified_liquid_content)
+    self.content = template.render(message_drops)
+  end
+
+  def modified_liquid_content
+    # This regex is used to match the code blocks in the content
+    # We don't want to process liquid in code blocks
+    content.gsub(/`(.*?)`/m, '{% raw %}`\\1`{% endraw %}')
+  end
+end