Fix for gravity form submission with page update in AMP native mode (amp-wp plugin)

rt-amp-gravity-form-fix.php

<?php
/**
 * Plugin Name: Gravity form fix for AMP-WP plugin
 * Description: Fix for gravity form submission with page update in AMP native mode (amp-wp plugin). Gravity forms submission with page update fix for AMP Native mode of amp-wp plugin. https://ampbyexample.com/components/amp-form/#form-submission-with-page-update
 * Plugin URI: https://gist.github.com/pradeep910/b25525034289ab0bc2b7fa0896f4ac90/
 * Version: 0.1
 * Author: Pradeep Sonawane
 * Author URI: https://pradeepsonawane.com
 *
 * @package rtCamp
 */

if ( ! function_exists( 'rt_is_amp_native' ) ) {
	/**
	 * Check if AMP native is enabled.
	 *
	 * @return bool
	 */
	function rt_is_amp_native() {

		return ( function_exists( 'is_amp_endpoint' ) && is_amp_endpoint() ) ? true : false;

	}
}

/**
 * Handle gravity form validation errors.
 *
 * @param  array $validation Validation array.
 *
 * @return array
 */
function rt_gform_handle_validation_error( $validation ) {

	if ( empty( $validation['is_valid'] ) && rt_is_amp_native() ) {

		if ( ! empty( $validation['form'] ) && ! empty( $validation['form']['fields'] ) ) {

			foreach ( $validation['form']['fields'] as $fields ) {

				if ( '' !== $fields['validation_message'] ) {

					// Add error messages as string.
					$errors .= sprintf(
						"<p><span class='error-field-name'>%s</span> <span class='error-field-message'>%s</span></p>", 
						$fields['label'], 
						str_replace( 'This', '', $fields['validation_message'] )
					);
				}
			}
		}

		wp_send_json( array(
			'error' => $errors
		), 300 );

		exit();
	}

	return $validation;

}

add_filter( 'gform_validation', 'rt_gform_handle_validation_error' );


/**
 * Support for gravity form submission with page update. https://ampbyexample.com/components/amp-form/#form-submission-with-page-update
 *
 * @param object $entry The entry that was just created via gravity form.
 *
 * @param array  $form The current form.
 */
function rt_redirect_gform_post_submission( $entry, $form) {

	if ( rt_is_amp_native() ) {

		$message = empty( $form['confirmation']['message'] ) ? sprintf( 'Thanks, this form has been submitted successfully!', 'rtcamp' ) : $form['confirmation']['message'];

		// Send gravity form confirmation message as success message via json.
		wp_send_json( array(
			'success' => $message
		) );

		exit();

	}

}

add_action( 'gform_after_submission', 'rt_redirect_gform_post_submission', 10, 2 );


/**
 * Filter Gravity form markup to add submit-success element.
 *
 * @param string $form_string Gravity form markup.
 * @param array  $form Gravity form fields.
 * @return string
 */
function rt_amp_gravity_form_filter( $form_string, $form ) {

	if( rt_is_amp_native() && ! strpos( $form_string, 'submit-success' ) ) {

		$form_string = str_replace(
			'</form>',
			sprintf(
				'<div submit-success>
					<template type="amp-mustache">
					{{{success}}}
					</template>
				</div>',
				'rtcamp'
			),
			$form_string
		);
	}

	return $form_string;

}

add_filter( 'gform_get_form_filter', 'rt_amp_gravity_form_filter', 10, 2 );

/**
 * Filters gravity form ajax attribute to disable ajax. Props Divyaraj Masani (@divyarajmasani)
 *
 * @param string $args post content.
 * @return array
 */
function rt_no_ajax_on_all_forms( $args ) {

	if( rt_is_amp_native() ) {
		$args['ajax'] = false;
	}

	return $args;
}

add_filter('gform_form_args', 'rt_no_ajax_on_all_forms', 10, 1);

// Use client-side validation UI instead of showing validation errors after page reload. Props Rahul Bansal at rtCamp.
add_filter( 'gform_field_content', function( $content, $field ) {

	if ( $field->isRequired && rt_is_amp_native() ) {
		return str_replace( 'aria-required=', 'required=', $content );
	}
	return $content;
}, 10, 2 );