AMP support for MailChimp for WordPress plugin

rt-amp-mailchimp-for-wordpress-fix.php

<?php
/**
 * Plugin Name: MailChimp for WordPress - AMP Support
 * Description: Fix for MailChimp form submission with page update in AMP.
 * Plugin URI: https://pradeepsonawane.com
 * Version: 0.1
 * Author: Pradeep Sonawane
 * Author URI: https://pradeepsonawane.com
 *
 * @package rtCamp
 */

/**
 * AMP - Mailchimp form error message handling.
 *
 * @param object $message Mailchimp Form Object.
 *
 * @return void
 */
function gk_amp_mailchimp_form_error_handling( $message ) {

	$post_form_id = intval( wp_unslash( $_POST['_mc4wp_form_id'] ) );

	if ( isset( $post_form_id ) && isset( $message->notices[0] ) ) {

		wp_send_json( [ 'error' => esc_html( $message->notices[0]->text ) ], 300 );

		die;
	}

}

add_action( 'mc4wp_form_error', 'gk_amp_mailchimp_form_error_handling' );

/**
 * AMP - Mailchimp form success message handling.
 *
 * @param object $message Mailchimp Form Object.
 *
 * @return void
 */
function gk_amp_mailchimp_form_success_handling( $message ) {

	$post_form_id = intval( wp_unslash( $_POST['_mc4wp_form_id'] ) );

	if ( isset( $post_form_id ) && isset( $message->notices[0] ) ) {

		wp_send_json( [ 'success' => esc_html( $message->notices[0]->text ) ], 200 );

		die;
	}

}

add_action( 'mc4wp_form_success', 'gk_amp_mailchimp_form_success_handling' );

/**
 * Mailchimp Form markup filtering for AMP page.
 * Add success message in the form markup.
 *
 * @param string $output Markup of Mailchimp form.
 *
 * @return string
 */
function gk_amp_mailchimp_form_filter( $output ) {

	if ( rt_is_amp() && ! strpos( $output, 'submit-success' ) ) {
		$output .= '<div submit-success><template type="amp-mustache">{{{success}}}</template></div>';
	}
	return $output;

}

add_filter( 'mc4wp_form_content', 'gk_amp_mailchimp_form_filter' );