refactor: strategy pattern for mailbox conversation finding (#12766)

Co-authored-by: Pranav <pranav@chatwoot.com>
Co-authored-by: Muhsin Keloth <muhsinkeramam@gmail.com>

app/mailboxes/imap/imap_mailbox.rb

@@ -3,6 +3,8 @@ class Imap::ImapMailbox
   include IncomingEmailValidityHelper
   attr_accessor :channel, :account, :inbox, :conversation, :processed_mail
 
+  FALLBACK_CONVERSATION_PATTERN = %r{account/(\d+)/conversation/([a-zA-Z0-9-]+)@}
+
   def process(mail, channel)
     @inbound_mail = mail
     @channel = channel
@@ -49,19 +51,32 @@ class Imap::ImapMailbox
   end
 
   def find_conversation_by_reference_ids
-    return if @inbound_mail.references.blank? && in_reply_to.present?
+    return if @inbound_mail.references.blank?
 
     message = find_message_by_references
+    if message.present?
+      conversation = @inbox.conversations.find_by(id: message.conversation_id)
+      return conversation if conversation.present?
+    end
 
-    return if message.nil?
-
-    @inbox.conversations.find(message.conversation_id)
+    # FALLBACK_PATTERN use to find a conversation that is started by an agent (no incoming message yet)
+    conversation_id = find_conversation_by_references
+    @inbox.conversations.find_by(uuid: conversation_id) if conversation_id.present?
   end
 
   def in_reply_to
     @processed_mail.in_reply_to
   end
 
+  def find_conversation_by_references
+    references = Array.wrap(@inbound_mail.references)
+    references.each do |message_id|
+      match = FALLBACK_CONVERSATION_PATTERN.match(message_id)
+
+      return match[2] if match.present?
+    end
+  end
+
   def find_message_by_references
     message_to_return = nil