Previously in the Building a Simple Email Log in Drupal7 blog entry I mentioned the Message module when creating a Sent Email Log for a client web application. The message module allows you to create activity streams of events in a system or store a history ledger of events. Messages support Drupal7 tokens out of the box — but they can also be more advanced; recently I was asked how to create a Message that was shown in the following requirements. Can Drupal do this?

Show a Message with the following text for Users:
"X has posted a new thread in the Y forum."
I've got a view that spits all of these out.
I now want to create a new view that shows the same messages, but in this view, I want to change the output of the above message to:
"You have posted a new thread in the Y forum."
Every time the node's author matches the currently authored user.

Sure Drupal can do this! The Message module supports some advanced tokenization methods, from its README file:

* Custom message arguments (Custom callbacks)
  When creating a message, it's possible to store custom arguments that will be replaced when presenting the message.
  E.g. If the message was created with an argument called "@sometext", it will get inserted to the message text (On display time) whenever the string "@sometext" is encountered.
  This method also supports custom call-back functions with optional arguments stored on the message; In order to use a callback, create the message with an argument such as:
  '!replaced-by-foo' => array(
    'callback' => 'foo',
    'callback arguments' => array('x', 'z')
  )
  That will get the string '!replaced-by-foo' in the message body to be replaced by the output of calling foo('x', 'z').

So we can use a custom callback in the message to change the value of a part of the Message upon display. We could define a message with text like, “!user has posted a new thread in forum Y.“.

When we create an instance of the message we can pass $arguments with a callback function to show our message. This callback is run every time the message is displayed to the screen — thus making a dynamic message! This code could look like:

$arguments['!user'] = array(
  'callback' => '_user_context_label',
  'callback arguments' => NULL,
  'pass message' => FALSE,
);
$message = message_create(
  'message_thread_notification',
  array('arguments' => $arguments)
);

This message would then call our custom defined function _user_context_label to provide a string fragment for our message. This function could look like:

function _user_context_label() {
  global $user; // The logged in user.
  $thread_user = current_thread->get_user();
  return ($user->uid == $thread_user->uid) ? t('You') : $thread_user->username;
}

I hope this helps to show you how to make more dynamic messages using the Message module. Happy Coding!

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