class Date_Widget extends WP_Widget {
	protected $default_instance = array(
		'date' => null,
	);

	public function __construct() {
		$widget_ops  = array(
			'classname'                   => 'widget_date',
			'description'                 => __( 'A date.', 'gutenberg' ),
			'customize_selective_refresh' => true,
		);
		$control_ops = array(
			'width'  => 200,
			'height' => 350,
		);
		parent::__construct( 'date', __( 'Date', 'gutenberg' ), $widget_ops, $control_ops );
	}

	public function widget( $args, $instance ) {
		echo $args['before_widget'];
		if ( $instance['date'] ) {
			echo $instance['date']->format( 'c' );
		}
		echo $args['after_widget'];
	}

	public function update( $new_instance, $old_instance ) {
		$instance = array_merge( $this->default_instance, $old_instance );
		if ( $new_instance['date'] ) {
			$instance['date'] = DateTime::createFromFormat( 'Y-m-d', $new_instance['date'] );
		} else {
			$instance['date'] = null;
		}
		return $instance;
	}

	public function form( $instance ) {
		$instance = wp_parse_args( (array) $instance, $this->default_instance );
		?>
		<p>
			<label for="<?php echo $this->get_field_id( 'date' ); ?>">Date:</label>
			<input
				id="<?php echo $this->get_field_id( 'date' ); ?>"
				class="widefat"
				name="<?php echo $this->get_field_name( 'date' ); ?>"
				type="date"
				value="<?php echo $instance['date'] ? $instance['date']->format( 'Y-m-d' ) : ''; ?>"
			/>
		</p>
		<?php
	}
}
add_action(
	'widgets_init',
	function() {
		register_widget( 'Date_Widget' );
	}
);