Database.php

<?php

require_once 'config.php';

class Database
{
    private $username;
    private $password;
    private $host;
    private $database;

    public function __construct()
    {
        $this->username = USERNAME;
        $this->password = PASSWORD;
        $this->host = HOST;
        $this->database = DATABASE;
    }

    public static function establishConnection() : PDO
    {
        $database = new self();
        return $database->connect();
    }

    public function connect()
    {
        try {
            $conn = new PDO(
                "mysql:host=$this->host;dbname=$this->database;charset=utf8mb4",
                $this->username,
                $this->password,
                array(
                    PDO::ATTR_ERRMODE => PDO::ERRMODE_EXCEPTION,
                    PDO::ATTR_PERSISTENT => false,
                    PDO::MYSQL_ATTR_INIT_COMMAND => "SET NAMES utf8mb4 COLLATE utf8mb4_general_ci"
                )
            );

            //$conn->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
            return $conn;
        }
        catch(PDOException $e){
            die("Connection failed ".$e->getMessage());
        }
    }
}