Simple Demo Widget

<?php
/**
 * widget-demo.php
 *
 * Our widget demo plugin
 *
 * @author: Caspar Green <https://caspar.green>
 * @package: widget-demo
 * @version: 1.0.0
 */

/**
 * @plugin
 * Plugin Name: Widget Demo
 * Plugin URI: http://caspar.green/
 * Description: A simple widget demo.
 * Version: 1.0.0
 * Author: Caspar Green
 * Author URI: http://caspar.green/
 */

namespace Caspar;

// Oh no you di'n't
if ( ! defined( 'ABSPATH' ) ) {
	exit( 'Oh no you di\'n\'t' );
}

class Widget_Demo extends \WP_Widget {

	protected $defaults;

	/**
	 * Widget_Demo constructor.
	 */
	public function __construct() {
		$this->defaults = array(
			'title'    => '',
			'image_id' => '',
			'caption'  => '',
			'link'     => ''
		);

		$widget_options = array(
			'classname'   => 'demo-widget',
			'description' => __( 'A Simple Demo Widget', 'caspar' )
		);
		parent::__construct( 'widget-demo', __( 'A Simple Demo Widget', 'caspar' ), $widget_options );
	}

	/**
	 * Form for entering widget info in the admin.
	 *
	 * @param array $instance
	 *
	 * @return null
	 */
	public function form( $instance ) {
		$instance = wp_parse_args( $instance, $this->defaults );
		extract( $instance );
		?>

		<p>
			<label for="<?php echo esc_attr( $this->get_field_id( 'title' ) ); ?>"><?php _e( 'Title', 'caspar' ); ?>
				:</label><br/>
			<input type="text" id="<?php echo esc_attr( $this->get_field_id( 'title' ) ); ?>"
			       name="<?php echo esc_attr( $this->get_field_name( 'title' ) ); ?>"
			       value="<?php echo esc_attr( $title ); ?>" class="widefat"/>
		</p>
		<hr>
		<p>
			<label
				for="<?php echo esc_attr( $this->get_field_id( 'image_id' ) ); ?>"><?php _e( 'Image ID:', 'caspar' ); ?>
				:</label>&nbsp;
			<input type="text" id="<?php echo esc_attr( $this->get_field_id( 'image_id' ) ); ?>"
			       name="<?php echo esc_attr( $this->get_field_name( 'image_id' ) ); ?>"
			       value="<?php echo esc_attr( $image_id ); ?>" class="widefat"/>
		</p>
		<p>
			<label for="<?php echo esc_attr( $this->get_field_id( 'caption' ) ); ?>"><?php _e( 'Caption', 'caspar' ); ?>
				:</label><br/>
			<input type="text" id="<?php echo esc_attr( $this->get_field_id( 'caption' ) ); ?>"
			       name="<?php echo esc_attr( $this->get_field_name( 'caption' ) ); ?>"
			       value="<?php echo esc_attr( $caption ); ?>" class="widefat"/>
		</p>
		<p>
			<label for="<?php echo esc_attr( $this->get_field_id( 'link' ) ); ?>"><?php _e( 'Link', 'caspar' ); ?>
				:</label><br/>
			<input type="text" id="<?php echo esc_attr( $this->get_field_id( 'link' ) ); ?>"
			       name="<?php echo esc_attr( $this->get_field_name( 'link' ) ); ?>"
			       value="<?php echo esc_attr( $link ); ?>" class="widefat"/>
		</p>

		<?php
	}

	/**
	 * Sanitize and save widget data.
	 *
	 * @param array $new_instance
	 * @param array $old_instance
	 *
	 * @return array
	 */
	public function update( $new_instance, $old_instance ) {
		$new_instance['title']    = sanitize_text_field( $new_instance['title'] );
		$new_instance['image_id'] = (int) $new_instance['image_id'];
		$new_instance['caption']  = sanitize_text_field( $new_instance['caption'] );
		$new_instance['link']     = esc_url_raw( $new_instance['link'] );

		return $new_instance;
	}

	/**
	 * Show the widget contents on the front end.
	 *
	 * @param array $args
	 * @param array $instance
	 */
	public function widget( $args, $instance ) {
		extract( $args );
		extract( $instance );

		echo $before_widget;

		if ( ! empty( $instance['title'] ) ) {
			echo $before_title . $instance['title'] . $after_title;
		}

		printf( '<p><a href="%1$s">%2$s</a><br>%3$s</p>',
			esc_url( $link ),
			wp_get_attachment_image( (int) $image_id, 'medium' ),
			esc_attr( $caption )
		);

		echo $after_widget;
	}

}

add_action( 'widgets_init', __NAMESPACE__ . '\\widget_init' );
/**
 * Initialize the widget.
 */
function widget_init() {
	register_widget( 'Caspar\Widget_Demo' );
}