session_start();
session_destroy();
session_start();

$DATABASE_HOST = 'localhost';
$DATABASE_USER = 'user';
$DATABASE_PASS = 'mdp';
$DATABASE_NAME = 'dbname';

$con = mysqli_connect($DATABASE_HOST, $DATABASE_USER, $DATABASE_PASS, $DATABASE_NAME);
if ( mysqli_connect_errno() ) {

    die ('Failed to connect to MySQL: ' . mysqli_connect_error());
}

if ( !isset($_POST['username'], $_POST['password']) ) {

    die ('Please fill both the username and password field!');
}

if ($stmt = $con->prepare('SELECT id, password FROM accounts WHERE username = ?')) {

    $stmt->bind_param('s', $_POST['username']);
    $stmt->execute();

    $stmt->store_result();

  if ($stmt->num_rows > 0) {
    $stmt->bind_result($id, $password);
    $stmt->fetch();

    if (password_verify($_POST['password'], $password)) {

        session_regenerate_id();
        $_SESSION['loggedin'] = TRUE;
        $_SESSION['name'] = $_POST['username'];
        $_SESSION['id'] = $id;
        header('Location: option.php');
    } else {
        echo 'Le mot de passe n\'est pas correcte !';
        $_SESSION['erreur'] = 'Le mot de passe n\'est pas correcte !';
        header('Location: login.php');
    }
} else {
    echo 'le nom d\'utilisateur n\'est pas correcte !';
    $_SESSION['erreur'] = 'le nom d\'utilisateur n\'est pas correcte !';
    header('Location: login.php');
}
$stmt->close();
}