<?php

use MongoDB\Driver\Manager;
use MongoDB\Driver\Query;
use MongoDB\Driver\ReadPreference;

class Database {
    private $Database;
    private static $Instance;

    public function __construct() {
        $Manager = new Manager("mongodb://localhost:27017", array(), array());
        $this->Database = $Manager;
    }

    public static function getInstance() {
        if (static::$Instance == null) {
            static::$Instance = new Database();
        }

        return static::$Instance;
    }

    public function query($scheme, $query) {
        return $this->Database->executeQuery($scheme, $query, new ReadPreference(ReadPreference::RP_PRIMARY));
    }
}

class App {
    public function run() {
        $db = Database::getInstance();
        
        $query = new Query(array());
        $cursor = $db->query("mydb.scheme_info", $query);

        foreach ($cursor as $document) {
            echo $document->value;
        }

        $query = new Query(array());
        $cursor = $db->query("mydb.domain", $query);

        foreach ($cursor as $document) {
            echo $document->hostname;
        }
    }
}

$App = new App();
$App->run();