A plain Date-Object without time-information – somehow

Date.php

<?php

/*
 * Copyright (c) Andreas Heigl <andreas@heigl.org>
 * 
 * Licensed under the MIT License. See LICENSE.md file in the project root
 * for full license information.
 */

namespace Org_Heigl\Date;

use DateInterval;
use DateTime;
use DateTimeImmutable;
use DateTimeZone;

class Date
{
    private $datetime;

    public function __construct($date, DateTimeZone $timezone = null)
    {
        $this->datetime = new DateTimeImmutable($date, $timezone);
        if (null !== $timezone) {
            $this->datetime->setTimezone($timezone);
        }
        $this->datetime = $this->datetime->setTime(12,00,00,0);
    }

    public function format($format) : string
    {
        // prepend all time-relevant information from the formatting string with
        // backslashes to escape them. THis format can only format date-information
        $this->datetime->format($format)
    }

    public function add(DateInterval $interval) : Date
    {
        // Remove all time-information from the interval. So everything behind the "T"
        $self = clone($this);
        $self->datetime->add($interval);

        return $self;
    }

    public function sub(DateInterval $interval) : Date
    {
        // Remove all time-information from the interval. So everything behind the "T"
        $self = clone($this);
        $self->datetime->sub($interval);

        return $self;
    }

    public function modify(string $modification) : Date
    {
        // Remove all time-information from modification-string
        $self = clone($this);
        $self->datetime->modify($modification);

        return $self;
    }

    public function diff(Date $date) : DateInterval
    {
        $interval = $this->datetime
                         ->setTimezone(new DateTimeZone('UTC'))
                         ->setTime(12,0,0,0)
                         ->diff(
                             $date->datetime
                                  ->setTimezone(new DateTimeZone('UTC')=
                                  ->setTime(12,0,0,0)
                         );

        // Remove all time-relevant informations from DateInterval (shouldn'T be there anyway)
        return $interval;

    }

    public function getTimezone() : DateTimeZone
    {
        return $this->datetime->getTimezone();
    }
}