/**
 * Check whether the Contact Form 7 plugin is active.
 * If not, deactivate this one and display error message in admin panel.
 */

register_activation_hook( __FILE__, 'wpcf7_check_CF7_is_active' );

function wpcf7_check_CF7_is_active () {

    if (! is_plugin_active('contact-form-7/wp-contact-form-7.php')) {

        wp_mail('support@andrewgolightly.com', 'CF7 not active', 'test');

        add_action( 'admin_init', 'wpcf7_deactivate_plugin' );
        add_action( 'admin_notices', 'wpcf7_display_deactivation_notice' );

        function wpcf7_deactivate_plugin () {
            wp_mail('support@andrewgolightly.com', 'deactivating plugin', 'test');
            deactivate_plugins( __FILE__ );
        }

        function wpcf7_display_deactivation_notice () {
            wp_mail('support@andrewgolightly.com', 'posting notice of deactivation', 'test');
            echo '<div class="updated"><p>The <strong>Contact Form 7 email verification</strong> plugin has been <em>deactivated</em>. Please first install and activate the <strong>Contact Form 7 plugin/strong></p></div>';

               if ( isset( $_GET['activate'] ) )
                    unset( $_GET['activate'] );

          }
    }
}