OOP for Better Conversions in WordPress Plugins | https://www.ibenic.com/oop-conversions-wordpress-plugins

admin.php

<?php

/**
* Get all integrations. If there are any integrations, the array will be:
* array(
*  'integration_slug' => 'My_Integration_Class'
* )
*/
$integrations = apply_filters( 'my_plugin_integrations', array() );

if( $integrations ) {
  foreach ( $integrations as $slug => $class ) {
    $integration_object = new $class(); ?>
    <div class="plugin-card plugin-card-<?php echo $slug; ?>">
      <div class="plugin-card-top">
        <div class="name column-name">
          <h3>
            <?php echo $integration_object->title; ?>					
            <img src="<?php echo $integration_object->image; ?>" class="plugin-icon" alt="">
          </h3>
        </div>
        <div class="desc column-description">
          <p><?php echo $integration_object->desc; ?></p>
        </div>
      </div>
      <div class="plugin-card-bottom">
        <?php $integration_object->buttons(); ?>
      </div>
  </div>
  <?php
  }
}
 
 

mailchimp-bottom.php

<?php

add_filter( 'my_plugin_integrations', 'integrate_mailchimp' );

/**
 * Registering mailchimp
 * @return array 
 */
function integrate_mailchimp( $integrations ) {

    $integrations['ga_mailchimp'] = 'GA_MailChimp';

    return $integrations;
}

mailchimp-free.php

<?php

if( ! class_exists( 'GA_MailChimp' ) ) {
  class GA_MailChimp extends GA_Integration {

  // ...
  }
}

mailchimp-pro.php

<?php
class GA_MailChimp extends GA_Integration {

    /**
     * Integration Image
     * @var string
     */
    public $image = '';

    /**
     * Integration Title
     * @var string
     */
    public $title = '';

    /**
     * Integration Description
     * @var string
     */
    public $desc = '';

    /**
     * Setting initial params
     */
    public function __construct() {

        $this->title = __( 'MailChimp', 'givasap' );
        $this->settings_id = 'ga_mailchimp';
        $this->image = 'https://static.mailchimp.com/web/brand-assets/mc_freddie_color_web.png';
        $this->desc = __( 'Sends users to your list and grow your email list', 'giveasap' );
        
        // Premium Features
        parent::__construct();

        add_filter( 'giveasap_send_registered_email', array( $this, 'send_default_email' ) );
        // ... All your premium features below
    }
    
    // All other premium methods are inside here. No method buttons() needed.

}

mailchimp.php

<?php
class GA_MailChimp extends GA_Integration {

    /**
     * Integration Image
     * @var string
     */
    public $image = '';

    /**
     * Integration Title
     * @var string
     */
    public $title = '';

    /**
     * Integration Description
     * @var string
     */
    public $desc = '';

    /**
     * Setting initial params
     */
    public function __construct() {

        $this->title = __( 'MailChimp', 'givasap' );
        $this->settings_id = 'ga_mailchimp';
        $this->image = 'https://static.mailchimp.com/web/brand-assets/mc_freddie_color_web.png';
        $this->desc = __( 'Sends users to your list and grow your email list', 'giveasap' );
    }

    public function buttons( $integrations ) {
        echo '<a href="' . giv_fs()->get_upgrade_url() . '" class="button button-primary">' . __( 'Upgrade to PRO', 'giveasap' ) . '</a>';
    }

}