Simple decorator pattern example

url-decorator.php

<?php # -*- coding: utf-8 -*-

interface Url {
	public function get_url();
}

class Basic_Url implements Url {

	private $url;

	public function __construct( $url ) {
		$this->url = $url;
	}

	public function get_url() {
		return $this->url;
	}
}

/**
 * Changes the the URL to be without protocol.
 */
class Url_Decorator implements Url {

	private $url;

	public function __construct( Url $url ) {
		$string = $url->get_url();
		$host = parse_url( $string, PHP_URL_HOST );

		if ( $host === $_SERVER[ 'HTTP_HOST' ] )
			$this->url = preg_replace( '~^https?:~', '', $string );
		else
			$this->url = $string;
	}

	public function get_url() {
		return $this->url;
	}
}

class Link_Builder {

	private $url;

	public function __construct( Url $url ) {
		$this->url = $url;
	}

	public function get_link() {
		return sprintf( '<a href="%1$s">%1$s</a>', $this->url->get_url() );
	}
}

$basic_url = new Basic_Url( 'http://' . $_SERVER['HTTP_HOST'] . '/foo' );

$link_1 = new Link_Builder(
	$basic_url
);
$link_2 = new Link_Builder( new Url_Decorator( $basic_url ) );

// normal
print $link_1->get_link() . '<br>';
print $link_2->get_link() . '<br>';