Add course (post) title as an email template and certificate merge code

[brianhogg]

Is your feature request related to a problem? Please describe.
When creating an engagement where the engagement type is sending an email, there's no merge tags to put things like the "related post" title into the email template. This means a separate template needs to be made for each course.

Similarly with certificates, it would be ideal if the same certificate template could be used across multiple courses.

Describe the solution you'd like
Merge code to insert the title of the related post ID that triggered the email. Also a merge code for the course title in a certificate (though this needs a check that there is one, as a certificate could be generated other ways)

[brianhogg]

Something like this should work in the child theme's functions.php:

// Add the merge code to the email editor's merge code button dropdown.
add_filter(
	'llms_merge_codes_for_button',
	function ( $codes, $screen ) {
		if ( $screen && 'llms_email' === ( $screen->post_type ?? '' ) ) {
			$codes['{course_title}'] = __( 'Related Post Title', 'lifterlms' );
		}
		return $codes;
	},
	10,
	2
);
// Inject the merge data into the engagement email before it sends.
add_action(
	'lifterlms_email_engagement_before_send',
	function ( $email ) {
		// The related_id isn't stored on the email object, but the engagement
		// handler passes it via compact() to get_email(). We can retrieve it
		// from the engagement handler's context by looking at the current
		// action's call stack, but the most reliable way is to stash it.
		// Since we also hook handle_email below, we read from our stash.
		$related_id = $GLOBALS['_llms_engagement_related_id'] ?? 0;
		if ( $related_id ) {
			$title = get_the_title( $related_id );
		} else {
			$title = '';
		}
		$email->add_merge_data(
			array(
				'{course_title}' => $title,
			)
		);
	}
);
// Stash related_id before handle_email() runs.
add_action(
	'lifterlms_engagement_send_email',
	function ( $args ) {
		$GLOBALS['_llms_engagement_related_id'] = $args[2] ?? '';
	},
	5
);

[brianhogg]

Example of merge code snippet for certificate https://lifterlms.com/docs/how-to-add-a-custom-merge-code-for-a-certificate/