fix: Do not allow sending messages if merged contact has a duplicate session (#11152)

In this PR https://github.com/chatwoot/chatwoot/pull/11139, if there is
an attempt to create a duplication session for the contact in the same
inbox, we will anonymize the old session.

This PR would prevent sending messages to the older sessions. The
support agents will have to create a new conversation to continue
messages with customer.

app/services/base/send_on_channel_service.rb

@@ -12,8 +12,10 @@ class Base::SendOnChannelService
 
   def perform
     validate_target_channel
+
     return unless outgoing_message?
     return if invalid_message?
+    return if invalid_source_id?
 
     perform_reply
   end
@@ -49,6 +51,29 @@ class Base::SendOnChannelService
     message.private? || outgoing_message_originated_from_channel?
   end
 
+  def invalid_source_id?
+    return false unless channels_to_validate?
+
+    return false if contact_inbox.source_id == expected_source_id
+
+    message.update!(status: :failed, external_error: I18n.t('errors.channel_service.invalid_source_id'))
+    true
+  end
+
+  def expected_source_id
+    ContactInbox::SourceIdService.new(
+      contact: contact,
+      channel_type: inbox.channel_type,
+      medium: inbox.channel.try(:medium)
+    ).generate
+  rescue ArgumentError
+    nil
+  end
+
+  def channels_to_validate?
+    inbox.sms? || inbox.whatsapp? || inbox.email? || inbox.twilio?
+  end
+
   def validate_target_channel
     raise 'Invalid channel service was called' if inbox.channel.class != channel_class
   end

app/services/contact_inbox/source_id_service.rb

@@ -0,0 +1,55 @@
+class ContactInbox::SourceIdService
+  pattr_initialize [:contact!, :channel_type!, { medium: nil }]
+
+  def generate
+    case channel_type
+    when 'Channel::TwilioSms'
+      twilio_source_id
+    when 'Channel::Whatsapp'
+      wa_source_id
+    when 'Channel::Email'
+      email_source_id
+    when 'Channel::Sms'
+      phone_source_id
+    when 'Channel::Api', 'Channel::WebWidget'
+      SecureRandom.uuid
+    else
+      raise ArgumentError, "Unsupported operation for this channel: #{channel_type}"
+    end
+  end
+
+  private
+
+  def email_source_id
+    raise ArgumentError, 'contact email required' unless contact.email
+
+    contact.email
+  end
+
+  def phone_source_id
+    raise ArgumentError, 'contact phone number required' unless contact.phone_number
+
+    contact.phone_number
+  end
+
+  def wa_source_id
+    raise ArgumentError, 'contact phone number required' unless contact.phone_number
+
+    # whatsapp doesn't want the + in e164 format
+    contact.phone_number.delete('+').to_s
+  end
+
+  def twilio_source_id
+    raise ArgumentError, 'contact phone number required' unless contact.phone_number
+    raise ArgumentError, 'medium required for Twilio channel' if medium.blank?
+
+    case medium
+    when 'sms'
+      contact.phone_number
+    when 'whatsapp'
+      "whatsapp:#{contact.phone_number}"
+    else
+      raise ArgumentError, "Unsupported Twilio medium: #{medium}"
+    end
+  end
+end