woocommerce checkout - login user if email exists

functions.php

add_action( 'woocommerce_before_checkout_process', 'wc_before_checkout_process', 999 ); // hook, function name, priority
function wc_before_checkout_process(){ // function name
	foreach ( WC()->cart->get_cart() as $cart_item ) { // loop wc cart
		$item_id = $cart_item['data']->get_id(); // item id
		$is_ticket = get_post_meta( $item_id, '_tutor_product', true ); // get post meta field '_tutor_product'
		if( $is_ticket ){ // if ticket
			if( isset( $_POST['primarycontactemail'] ) ){ // if field exists
				if ( !empty( $_POST['primarycontactemail'] ) ){ // if field not empty
					if ( ! is_user_logged_in() ) { // if user not logged in
						nocache_headers(); // clear headers
						wp_clear_auth_cookie(); // clear cookie
						$user_id = email_exists( $_POST['primarycontactemail'] ); // get user id by email from email field
						wp_set_auth_cookie( $user_id ); // set auth cookie
						WC()->session->set( 'reload_checkout', true ); // reload page and log-in user
					}
				}
			}
		}			
	}
}