Email Domain Validator

<?php
/**
 * Gravity Wiz // Gravity Forms // Email Domain Validator
 * https://gravitywiz.com/banlimit-email-domains-for-gravity-form-email-fields/
 *
 * Allows you to exclude a list of invalid domains or include a list of valid domains for your Gravity Form Email fields.
 *
 * Plugin Name:  Gravity Forms - Email Domain Validator
 * Plugin URI:   https://gravitywiz.com/banlimit-email-domains-for-gravity-form-email-fields/
 * Description:  Exclude a list of invalid domains or include a list of valid domains for your Gravity Form Email fields.
 * Author:       Gravity Wiz
 * Version:      0.1
 * Author URI:   https://gravitywiz.com/
 */
class GW_Email_Domain_Validator {

	private $_args;

	function __construct( $args ) {

		$this->_args = wp_parse_args( $args, array(
			'form_id'            => false,
			'field_id'           => false,
			'domains'            => false,
			// translators: placeholder is a domain for emails that are not allowed.
			'validation_message' => __( 'Sorry, <strong>%s</strong> email accounts are not eligible for this form.' ),
			'mode'               => 'ban', // also accepts "limit"
		) );

		// convert field ID to an array for consistency, it can be passed as an array or a single ID
		if ( $this->_args['field_id'] && ! is_array( $this->_args['field_id'] ) ) {
			$this->_args['field_id'] = array( $this->_args['field_id'] );
		}

		$form_filter = $this->_args['form_id'] ? "_{$this->_args['form_id']}" : '';

		add_filter( "gform_validation{$form_filter}", array( $this, 'validate' ) );

	}

	function validate( $validation_result ) {

		$form = $validation_result['form'];

		foreach ( $form['fields'] as &$field ) {

			// if this is not an email field, skip
			if ( RGFormsModel::get_input_type( $field ) != 'email' ) {
				continue;
			}

			// if field ID was passed and current field is not in that array, skip
			if ( $this->_args['field_id'] && ! in_array( $field['id'], $this->_args['field_id'] ) ) {
				continue;
			}

			$page_number = GFFormDisplay::get_source_page( $form['id'] );
			if ( $page_number > 0 && $field->pageNumber != $page_number ) {
				continue;
			}

			if ( GFFormsModel::is_field_hidden( $form, $field, array() ) ) {
				continue;
			}

			$domain = $this->get_email_domain( $field );

			// if domain is valid OR if the email field is empty, skip
			if ( $this->is_domain_valid( $domain ) || empty( $domain ) ) {
				continue;
			}

			$validation_result['is_valid'] = false;
			$field['failed_validation']    = true;
			$field['validation_message']   = sprintf( $this->_args['validation_message'], $domain );

		}

		$validation_result['form'] = $form;
		return $validation_result;
	}

	function get_email_domain( $field ) {
		$email = explode( '@', rgpost( "input_{$field['id']}" ) );
		return trim( rgar( $email, 1 ) );
	}

	function is_domain_valid( $domain ) {

		$mode   = $this->_args['mode'];
		$domain = strtolower( $domain );

		foreach ( $this->_args['domains'] as $_domain ) {

			$_domain = strtolower( $_domain );

			$full_match   = $domain == $_domain;
			$suffix_match = strpos( $_domain, '.' ) === 0 && $this->string_ends_with( $domain, $_domain );
			$has_match    = $full_match || $suffix_match;

			if ( $mode == 'ban' && $has_match ) {
				return false;
			} elseif ( $mode == 'limit' && $has_match ) {
				return true;
			}
		}

		return $mode == 'limit' ? false : true;
	}

	function string_ends_with( $string, $text ) {

		$length      = strlen( $string );
		$text_length = strlen( $text );

		if ( $text_length > $length ) {
			return false;
		}

		return substr_compare( $string, $text, $length - $text_length, $text_length ) === 0;
	}

}

class GWEmailDomainControl extends GW_Email_Domain_Validator { }

# Configuration

new GW_Email_Domain_Validator( array(
	'form_id'            => 326,
	'field_id'           => 1,
	'domains'            => array( 'gmail.com', 'hotmail.com', '.co.uk' ),
	// translators: placeholder is a domain for emails that are not allowed.
	'validation_message' => __( 'Oh no! <strong>%s</strong> email accounts are not eligible for this form.' ),
	'mode'               => 'limit',
) );