doitinpoland.com/wp-content/plugins/mailchimp-for-wp/integrations/woocommerce/class-woocommerce.php

<?php

defined( 'ABSPATH' ) or exit;

/**
 * Class MC4WP_WooCommerce_Integration
 *
 * @ignore
 */
class MC4WP_WooCommerce_Integration extends MC4WP_Integration {


	/**
	 * @var string
	 */
	public $name = 'WooCommerce Checkout';

	/**
	 * @var string
	 */
	public $description = "Subscribes people from WooCommerce's checkout form.";

	/**
	 * Add hooks
	 */
	public function add_hooks() {
		if ( ! $this->options['implicit'] ) {

			if ( $this->options['position'] !== 'after_email_field' ) {

				// create hook name based on position setting
				$hook = $this->options['position'];
				if ( strpos( $hook, 'cfw_' ) !== 0 && strpos( $hook, 'woocommerce_' ) !== 0 ) {
					$hook = sprintf( 'woocommerce_%s', $hook );
				}

				add_action( $hook, array( $this, 'output_checkbox' ), 20 );
			} else {
				add_filter( 'woocommerce_form_field_email', array( $this, 'add_checkbox_after_email_field' ), 10, 4 );
			}

			add_action( 'woocommerce_checkout_update_order_meta', array( $this, 'save_woocommerce_checkout_checkbox_value' ) );

			// specific hooks for klarna
			add_filter( 'kco_create_order', array( $this, 'add_klarna_field' ) );
			add_filter( 'klarna_after_kco_confirmation', array( $this, 'subscribe_from_klarna_checkout' ), 10, 2 );

		}

		add_action( 'woocommerce_checkout_order_processed', array( $this, 'subscribe_from_woocommerce_checkout' ) );
	}

	/**
	 * Add default value for "position" setting
	 *
	 * @return array
	 */
	protected function get_default_options() {
		$defaults             = parent::get_default_options();
		$defaults['position'] = 'billing';
		return $defaults;
	}

	public function add_klarna_field( $create ) {
		$create['options']['additional_checkbox']['text']     = $this->get_label_text();
		$create['options']['additional_checkbox']['checked']  = (bool) $this->options['precheck'];
		$create['options']['additional_checkbox']['required'] = false;
		return $create;
	}

	function add_checkbox_after_email_field( $field, $key, $args, $value ) {
		if ( $key !== 'billing_email' ) {
			return $field;
		}

		$field .= PHP_EOL;
		$field .= $this->get_checkbox_html(
			array(
				'class' => 'form-row form-row-wide',
			)
		);
		return $field;
	}

	/**
	* @param int $order_id
	*/
	public function save_woocommerce_checkout_checkbox_value( $order_id ) {
		update_post_meta( $order_id, '_mc4wp_optin', $this->checkbox_was_checked() );
	}

	/**
	 * {@inheritdoc}
	 *
	 * @param $order_id
	 *
	 * @return bool|mixed
	 */
	public function triggered( $order_id = null ) {
		if ( $this->options['implicit'] ) {
			return true;
		}

		if ( ! $order_id ) {
			return false;
		}

		$do_optin = get_post_meta( $order_id, '_mc4wp_optin', true );
		return $do_optin;
	}

	public function subscribe_from_klarna_checkout( $order_id, $klarna_order ) {
		// $klarna_order is the returned object from Klarna
		if ( false === (bool) $klarna_order['merchant_requested']['additional_checkbox'] ) {
			return;
		}

		// get back into regular subscribe flow
		update_post_meta( $order_id, '_mc4wp_optin', true );
		$this->subscribe_from_woocommerce_checkout( $order_id );
		return;
	}

	/**
	* @param int $order_id
	* @return boolean
	*/
	public function subscribe_from_woocommerce_checkout( $order_id ) {
		if ( ! $this->triggered( $order_id ) ) {
			return false;
		}

		$order = wc_get_order( $order_id );

		if ( method_exists( $order, 'get_billing_email' ) ) {
			$data = array(
				'EMAIL' => $order->get_billing_email(),
				'NAME'  => "{$order->get_billing_first_name()} {$order->get_billing_last_name()}",
				'FNAME' => $order->get_billing_first_name(),
				'LNAME' => $order->get_billing_last_name(),
			);
		} else {
			// NOTE: for compatibility with WooCommerce < 3.0
			$data = array(
				'EMAIL' => $order->billing_email,
				'NAME'  => "{$order->billing_first_name} {$order->billing_last_name}",
				'FNAME' => $order->billing_first_name,
				'LNAME' => $order->billing_last_name,
			);
		}

		// TODO: add billing address fields, maybe by finding Mailchimp field of type "address"?

		return $this->subscribe( $data, $order_id );
	}

	/**
	 * @return bool
	 */
	public function is_installed() {
		return class_exists( 'WooCommerce' );
	}

	/**
	 * {@inheritdoc}
	 *
	 * @return string
	 */
	public function get_object_link( $object_id ) {
		return sprintf( '<a href="%s">%s</a>', get_edit_post_link( $object_id ), sprintf( __( 'Order #%d', 'mailchimp-for-wp' ), $object_id ) );
	}
}