EmailNotifier.php

<?php

interface EmailNotifierInterface {
    /**
     * Client was successfully charged for a project
     * 
     * context: payment_history model (with access to project & invoice)
     */
    const NOTIFICATION_CHARGED = 'charged';
    
    /**
     * There was an error when processing a recurring payment
     * 
     * context: project model
     **/
    const NOTIFICATION_FAILED = 'failed';
    
    /**
     * The payment failed and project was suspended
     * 
     * context: project model
     **/
    const NOTIFICATION_SUSPENDED = 'suspended';
    
    /**
     * @param string $notificationType — one of the types defined above
     * @param mixed $context — see the context description for each type
     **/
    public function notify($notificationType, $context);
}