WordPress Gists embed Shortcode

gistfile1.php

<?php

/**
 * WordPress Gists Shortcode
 * 
 * To include a Gist you have different possibilities:
 * [gists id="5964192"]
 * [gists]https://gist.github.com/micc83/5964192[/gists]
 * [gists id="5964192" file="index.html"]
 * [gists file="index.html"]https://gist.github.com/micc83/5964192[/gists]
 * [gists https://gist.github.com/micc83/5964192 /]
 * [gists https://gist.github.com/micc83/5964192 file="index.html /]
 * 
 * @var Array|String $atts Shortcode attributes
 * @var String $content Shortcode content
 * 
 * @return String Gists embed script
 */
function minimamente_gists( $atts, $content = null ) {

	extract( shortcode_atts( array(
		'id' 	=> 	'',
		'file' 	=>	''
	), $atts ) );
	
	$gists_url = 'https://gist.github.com/';
	
	if ( empty( $content ) && isset( $atts[0] ) )
		$content = $atts[0];
	
	if  ( !empty ( $content ) ) {
	
		$url_parts = explode( '#', $content );
		$url = $url_parts[0] . '.js';
		
	} elseif ( ! empty( $id ) ) {
		
		$url = $gists_url . $id . '.js';
		
	} else {
	
		return false;
	
	}
	
	if ( !empty( $file ) )
		$url = add_query_arg( array( 'file' => $file ), $url );
	
	if ( ( ! $url = esc_url( $url ) ) || 0 !== stripos( $url, $gists_url ) )
		return false;

	return '<script src="'. $url .'"></script>';
}
add_shortcode( 'gists', 'minimamente_gists' );