cx-newsletter/pages/1-customers_export_page.php

<?php

namespace cx_newsletter;

class customers_export_page 
extends service 
implements service_interface {
    public function process() : self {
        return $this;
    }

    public function prepare() : self {
        \add_rewrite_rule(
            'cx-newsletter/customers-export$',
            'index.php?'.$this->param.'=1',
            'top'
        );

        global $wp_rewrite;
        $wp_rewrite->flush_rules(true);

        \add_filter('query_vars', [$this, 'add_query_var']);
        \add_action('parse_request', [$this, 'parse_request']);

        return $this;
    }

    public function add_query_var(array $vars) : array {
        array_push($vars, $this->param);
        return $vars;
    }

    public function parse_request($request) : void {
        if (!array_key_exists($this->param, $request->query_vars)) {
            return;
        }

        if (!\current_user_can('export')) {
            echo('You must login as user that could export content.');
            exit();
        }   
        
        $mapper = new customers_mapper(
            $this->get_database(),
            $this->get_tables()
        );

        $converter = new customers_converter();

        $all = [];

        foreach ($mapper->load_all() as $customer) {
            $customer = $converter->load_object($customer)->get_array();
            unset($customer['id']);
            array_push($all, $customer);
        }

        echo(json_encode($all));
        header("Content-Type: application/json");
        
        exit();
    }

    private string $param = 'cx_newsletter_must_export_customers_now';
}