<?php
/**
 * Torrent
 *
 * PHP version 5.2+ (with cURL extention enabled)
 *
 * LICENSE: This source file is subject to version 3 of the GNU GPL
 * that is available through the world-wide-web at the following URI:
 * http://www.gnu.org/licenses/gpl.html. If you did not receive a copy of
 * the GNU GPL License and are unable to obtain it through the web, please
 * send a note to adrien.gibrat@gmail.com so I can mail you a copy.
 *
 * 1) Features:
 * - Decode torrent file or data from local file and distant url
 * - Build torrent from source folder/file(s) or distant url
 * - Super easy usage & syntax
 * - Silent Exception error system
 *
 * 2) Usage example
 * <code>
require_once 'Torrent.php';

// get torrent infos
$torrent = new Torrent( './test.torrent' );
echo '<br>private: ', $torrent->is_private() ? 'yes' : 'no', 
	 '<br>announce: ', $torrent->announce(), 
	 '<br>name: ', $torrent->name(), 
	 '<br>comment: ', $torrent->comment(), 
	 '<br>piece_length: ', $torrent->piece_length(), 
	 '<br>size: ', $torrent->size( 2 ),
	 '<br>hash info: ', $torrent->hash_info(),
	 '<br>stats: ';
var_dump( $torrent->scrape() );
echo '<br>content: ';
var_dump( $torrent->content() );
echo '<br>source: ',
	 $torrent;

// get magnet link
$torrent->magnet(); // use $torrent->magnet( false ); to get non html encoded ampersand

// create torrent
$torrent = new Torrent( array( 'test.mp3', 'test.jpg' ), 'http://torrent.tracker/annonce' );
$torrent->save('test.torrent'); // save to disk

// modify torrent
$torrent->announce('http://alternate-torrent.tracker/annonce'); // add a tracker
$torrent->announce(false); // reset announce trackers
$torrent->announce(array('http://torrent.tracker/annonce', 'http://alternate-torrent.tracker/annonce')); // set tracker(s), it also works with a 'one tracker' array...
$torrent->announce(array(array('http://torrent.tracker/annonce', 'http://alternate-torrent.tracker/annonce'), 'http://another-torrent.tracker/annonce')); // set tiered trackers
$torrent->comment('hello world');
$torrent->name('test torrent');
$torrent->is_private(true);
$torrent->httpseeds('http://file-hosting.domain/path/'); // BitTornado implementation
$torrent->url_list(array('http://file-hosting.domain/path/','http://another-file-hosting.domain/path/')); // 
GetRight implementation

// print errors
if ( $errors = $torrent->errors() )
	var_dump( $errors );

// send to user
$torrent->send();
 * </code>
 *
 * @author   Adrien Gibrat <adrien.gibrat@gmail.com>
 * @tester   Jeong, Anton, dokcharlie, official testers ;) Thanks for your precious feedback
 * @copyleft 2010 - Just use it!
 * @license  http://www.gnu.org/licenses/gpl.html GNU General Public License version 3
 * @version  0.0.3
 */

class Torrent {
	
	/**
	* @const float Default http timeout
	*/
	const timeout = 30;

	/**
	* @var array List of error occurred
	*/
	static protected $_errors = array();

	/** Read and decode torrent file/data OR build a torrent from source folder/file(s)
	 * Supported signatures:
	 * - Torrent(); // get an instance (useful to scrape and check errors)
	 * - Torrent( string $torrent ); // analyze a torrent file
	 * - Torrent( string $torrent, string $announce );
	 * - Torrent( string $torrent, array $meta );
	 * - Torrent( string $file_or_folder ); // create a torrent file
	 * - Torrent( string $file_or_folder, string $announce_url, [int $piece_length] );
	 * - Torrent( string $file_or_folder, array $meta, [int $piece_length] );
	 * - Torrent( array $files_list );
	 * - Torrent( array $files_list, string $announce_url, [int $piece_length] );
	 * - Torrent( array $files_list, array $meta, [int $piece_length] );
	 * @param string|array torrent to read or source folder/file(s) (optional, to get an instance)
	 * @param string|array announce url or meta informations (optional)
	 * @param int piece length (optional)
	 */
	public function __construct ( $data = null, $meta = array(), $piece_length = 256 ) {
		if ( is_null( $data ) )
			return false;
		if ( $piece_length < 32 || $piece_length > 4096 )
			return self::set_error( new Exception( 'Invalid piece length, must be between 32 and 4096' ) );
		if ( is_string( $meta ) )
			$meta = array( 'announce' => $meta );
		if ( $this->build( $data, $piece_length * 1024 ) )
			$this->touch();
		else
			$meta = array_merge( $meta, $this->decode( $data ) );
		foreach( $meta as $key => $value )
			$this->{$key} = $value;
	}

	/** Convert the current Torrent instance in torrent format
	 * @return string encoded torrent data
	 */
	public function __toString() {
		return $this->encode( $this );
	}

	/** Return last error message
	 * @return string|boolean last error message or false if none
	 */
	public function error() {
		return empty( self::$_errors ) ?
			false :
			self::$_errors[0]->getMessage();
	}

	/** Return Errors
	 * @return array|boolean error list or false if none
	 */
	public function errors() {
		return empty( self::$_errors ) ?
			false :
			self::$_errors;
	}

	/**** Getters and setters ****/

	/** Getter and setter of torrent announce url / list
	 * If the argument is a string, announce url is added to announce list (or set as announce if announce is not set)
	 * If the argument is an array/object, set announce url (with first url) and list (if array has more than one url), tiered list supported
	 * If the argument is false announce url & list are unset
	 * @param null|false|string|array announce url / list, reset all if false (optional, if omitted it's a getter)
	 * @return string|array|null announce url / list or null if not set
	 */
	public function announce ( $announce = null ) {
		if ( is_null( $announce ) )
			return ! isset( $this->{'announce-list'} ) ?
				isset( $this->announce ) ? $this->announce : null :
				$this->{'announce-list'};
		$this->touch();
		if ( is_string( $announce ) && isset( $this->announce ) )
			return $this->{'announce-list'} = self::announce_list( isset( $this->{'announce-list'} ) ? $this->{'announce-list'} : $this->announce, $announce );
		unset( $this->{'announce-list'} );
		if ( is_array( $announce ) || is_object( $announce ) )
			if ( ( $this->announce = self::first_announce( $announce ) ) && count( $announce ) > 1 )
				return $this->{'announce-list'} = self::announce_list( $announce );
			else
				return $this->announce;
		if ( ! isset( $this->announce ) && $announce )
			return $this->announce = (string) $announce;
		unset( $this->announce );
	}

	/** Getter and setter of torrent creation date
	 * @param null|integer timestamp (optional, if omitted it's a getter)
	 * @return integer|null timestamp or null if not set
	 */
	public function creation_date ( $timestamp = null ) {
		return is_null( $timestamp ) ?
			isset( $this->{'creation date'} ) ? $this->{'creation date'} : null :
			$this->touch( $this->{'creation date'} = (int) $timestamp );
	}
	
	/** Getter and setter of torrent comment
	 * @param null|string comment (optional, if omitted it's a getter)
	 * @return string|null comment or null if not set
	 */
	public function comment ( $comment = null ) {
		return is_null( $comment ) ?
			isset( $this->comment ) ? $this->comment : null :
			$this->touch( $this->comment = (string) $comment );
	}

	/** Getter and setter of torrent name
	 * @param null|string name (optional, if omitted it's a getter)
	 * @return string|null name or null if not set
	 */
	public function name ( $name = null ) {
		return is_null( $name ) ?
			isset( $this->info['name'] ) ? $this->info['name'] : null :
			$this->touch( $this->info['name'] = (string) $name );
	}

	/** Getter and setter of private flag
	 * @param null|boolean is private or not (optional, if omitted it's a getter)
	 * @return boolean private flag
	 */
	public function is_private ( $private = null ) {
		return is_null( $private ) ?
			! empty( $this->info['private'] ) :
			$this->touch( $this->info['private'] = $private ? 1 : 0 );
	}

	/** Getter and setter of torrent source
	 * @param null|string source (optional, if omitted it's a getter)
	 * @return string|null source or null if not set
	 */
	public function source ( $source = null ) {
		return is_null( $source ) ?
			isset( $this->info['source'] ) ? $this->info['source'] : null :
			$this->touch( $this->info['source'] = (string) $source );

	}

	/** Getter and setter of webseed(s) url list ( GetRight implementation )
	 * @param null|string|array webseed or webseeds mirror list (optional, if omitted it's a getter)
	 * @return string|array|null webseed(s) or null if not set
	 */
	public function url_list ( $urls = null ) {
		return is_null( $urls ) ?
			isset( $this->{'url-list'} ) ? $this->{'url-list'} : null :
			$this->touch( $this->{'url-list'} = is_string( $urls) ? $urls : (array) $urls );
	}

	/** Getter and setter of httpseed(s) url list ( BitTornado implementation )
	 * @param null|string|array httpseed or httpseeds mirror list (optional, if omitted it's a getter)
	 * @return array|null httpseed(s) or null if not set
	 */
	public function httpseeds ( $urls = null ) {
		return is_null( $urls ) ?
			isset( $this->httpseeds ) ? $this->httpseeds : null :
			$this->touch( $this->httpseeds = (array) $urls );
	}

	/**** Analyze BitTorrent ****/

	/** Get piece length
	 * @return integer piece length or null if not set
	 */
	public function piece_length () {
		return isset( $this->info['piece length'] ) ?
			$this->info['piece length'] :
			null;
	}

	/** Compute hash info
	 * @return string hash info or null if info not set
	 */
	public function hash_info () {
		return isset( $this->info ) ?
			sha1( self::encode( $this->info ) ) :
			null;
	}

	/** List torrent content
	 * @param integer|null size precision (optional, if omitted returns sizes in bytes)
	 * @return array file(s) and size(s) list, files as keys and sizes as values
	 */
	public function content ( $precision = null ) {
		$files = array();
		if ( isset( $this->info['files'] ) && is_array( $this->info['files'] ) )
			foreach ( $this->info['files'] as $file )
				$files[self::path( $file['path'], $this->info['name'] )] = $precision ?
					self::format( $file['length'], $precision ) :
					$file['length'];
		elseif ( isset( $this->info['name'] ) )
				$files[$this->info['name']] = $precision ?
					self::format( $this->info['length'], $precision ) :
					$this->info['length'];
		return $files;
	}

	/** List torrent content pieces and offset(s)
	 * @return array file(s) and pieces/offset(s) list, file(s) as keys and pieces/offset(s) as values
	 */
	public function offset () {
		$files = array();
		$size = 0;
		if ( isset( $this->info['files'] ) && is_array( $this->info['files'] ) )
			foreach ( $this->info['files'] as $file )
				$files[self::path( $file['path'], $this->info['name'] )] = array(
					'startpiece'	=> floor( $size / $this->info['piece length'] ),
					'offset'	=> fmod( $size, $this->info['piece length'] ),
					'size'		=> $size += $file['length'],
					'endpiece'	=> floor( $size / $this->info['piece length'] )
				);
		elseif ( isset( $this->info['name'] ) )
				$files[$this->info['name']] = array(
					'startpiece'	=> 0,
					'offset'	=> 0,
					'size'		=> $this->info['length'],
					'endpiece'	=> floor( $this->info['length'] / $this->info['piece length'] )
				);
		return $files;
	}

	/** Sum torrent content size
	 * @param integer|null size precision (optional, if omitted returns size in bytes)
	 * @return integer|string file(s) size
	 */
	public function size ( $precision = null ) {
		$size = 0;
		if ( isset( $this->info['files'] ) && is_array( $this->info['files'] ) )
			foreach ( $this->info['files'] as $file )
				$size += $file['length'];
		elseif ( isset( $this->info['name'] ) )
				$size = $this->info['length'];
		return is_null( $precision ) ?
			$size :
			self::format( $size, $precision );
	}

	/** Request torrent statistics from scrape page USING CURL!!
	 * @param string|array announce or scrape page url (optional, to request an alternative tracker BUT required for static call)
	 * @param string torrent hash info (optional, required ONLY for static call)
	 * @param float read timeout in seconds (optional, default to self::timeout 30s)
	 * @return array tracker torrent statistics
	 */
	/* static */ public function scrape ( $announce = null, $hash_info = null, $timeout = self::timeout ) {
		$packed_hash = urlencode( pack('H*', $hash_info ? $hash_info : $this->hash_info() ) );
		$handles = $scrape = array();
		if ( ! function_exists( 'curl_multi_init' ) )
			return self::set_error( new Exception( 'Install CURL with "curl_multi_init" enabled' ) );
		$curl = curl_multi_init();
		foreach ( (array) ($announce ? $announce : $this->announce()) as $tier )
			foreach ( (array) $tier as $tracker ) {
				$tracker = str_ireplace( array( 'udp://', '/announce', ':80/' ), array( 'http://', '/scrape', '/' ), $tracker );
				if ( isset( $handles[$tracker] ) )
					continue;
				$handles[$tracker] = curl_init( $tracker . '?info_hash=' . $packed_hash );
				curl_setopt( $handles[$tracker], CURLOPT_RETURNTRANSFER, true );
				curl_setopt( $handles[$tracker], CURLOPT_TIMEOUT, $timeout );
				curl_multi_add_handle( $curl, $handles[$tracker] );
			}
		do {
			while ( ( $state = curl_multi_exec( $curl, $running ) ) == CURLM_CALL_MULTI_PERFORM );
				if( $state != CURLM_OK )
					continue;
			while ( $done = curl_multi_info_read( $curl ) ) {
				$info = curl_getinfo( $done['handle'] );
				$tracker = explode( '?', $info['url'], 2 );
				$tracker = array_shift( $tracker );
				if ( empty( $info['http_code'] ) ) {
					$scrape[$tracker] = self::set_error( new Exception( 'Tracker request timeout (' . $timeout . 's)' ), true );
					continue;
				} elseif ( $info['http_code'] != 200 ) {
					$scrape[$tracker] = self::set_error( new Exception( 'Tracker request failed (' . $info['http_code'] . ' code)' ), true );
					continue;
				}
				$data = curl_multi_getcontent( $done['handle'] );
				$stats = self::decode_data( $data );
				curl_multi_remove_handle( $curl, $done['handle'] );
				$scrape[$tracker] = empty( $stats['files'] ) ?
					self::set_error( new Exception( 'Empty scrape data' ), true ) :
					array_shift( $stats['files'] ) + ( empty( $stats['flags'] ) ? array() : $stats['flags'] );
			}
		} while ( $running );
		curl_multi_close( $curl );
		return $scrape;
	}

	/**** Save and Send ****/

	/** Save torrent file to disk
	 * @param null|string name of the file (optional)
	 * @return boolean file has been saved or not
	 */
	public function save ( $filename = null ) {
		return file_put_contents( is_null( $filename ) ? $this->info['name'] . '.torrent' : $filename, $this->encode( $this ) );
	}

	/** Send torrent file to client
	 * @param null|string name of the file (optional)
	 * @return void script exit
	 */
	public function send ( $filename = null ) {
		$data = $this->encode( $this );
		header( 'Content-type: application/x-bittorrent' );
		header( 'Content-Length: ' . strlen( $data ) );
		header( 'Content-Disposition: attachment; filename="' . ( is_null( $filename ) ? $this->info['name'] . '.torrent' : $filename ) . '"' );
		exit( $data );
	}

	/** Get magnet link
	 * @param boolean html encode ampersand, default true (optional)
	 * @return string magnet link
	 */
	public function magnet ( $html = true ) {
		$ampersand = $html ? '&amp;' : '&';
		return sprintf( 'magnet:?xt=urn:btih:%2$s%1$sdn=%3$s%1$sxl=%4$d%1$str=%5$s', $ampersand, $this->hash_info(), urlencode( $this->name() ), $this->size(), implode( $ampersand .'tr=', self::untier( $this->announce() ) ) );
	}	

	/**** Encode BitTorrent ****/

	/** Encode torrent data
	 * @param mixed data to encode
	 * @return string torrent encoded data
	 */
	static public function encode ( $mixed ) {
		switch ( gettype( $mixed ) ) {
			case 'integer':
			case 'double':
				return self::encode_integer( $mixed );
			case 'object':
				$mixed = get_object_vars( $mixed );
			case 'array':
				return self::encode_array( $mixed );
			default:
				return self::encode_string( (string) $mixed );
		}
	}

	/** Encode torrent string
	 * @param string string to encode
	 * @return string encoded string
	 */
	static private function encode_string ( $string ) {
		return strlen( $string ) . ':' . $string;
	}

	/** Encode torrent integer
	 * @param integer integer to encode
	 * @return string encoded integer
	 */
	static private function encode_integer ( $integer ) {
		return 'i' . $integer . 'e';
	}

	/** Encode torrent dictionary or list
	 * @param array array to encode
	 * @return string encoded dictionary or list
	 */
	static private function encode_array ( $array ) {
		if ( self::is_list( $array ) ) {
			$return = 'l';
			foreach ( $array as $value )
				$return .= self::encode( $value );
		} else {
			ksort( $array, SORT_STRING );
			$return = 'd';
			foreach ( $array as $key => $value )
				$return .= self::encode( strval( $key ) ) . self::encode( $value );
		}
		return $return . 'e';
	}

	/**** Decode BitTorrent ****/

	/** Decode torrent data or file
	 * @param string data or file path to decode
	 * @return array decoded torrent data
	 */
	static protected function decode ( $string ) {
		$data = is_file( $string ) || self::url_exists( $string ) ?
			self::file_get_contents( $string ) :
			$string;
		return (array) self::decode_data( $data );
	}

	/** Decode torrent data
	 * @param string data to decode
	 * @return array decoded torrent data
	 */
	static private function decode_data ( & $data ) {
		switch( self::char( $data ) ) {
		case 'i':
			$data = substr( $data, 1 );
			return self::decode_integer( $data );
		case 'l':
			$data = substr( $data, 1 );
			return self::decode_list( $data );
		case 'd':
			$data = substr( $data, 1 );
			return self::decode_dictionary( $data );
		default:
			return self::decode_string( $data );
		}
	}

	/** Decode torrent dictionary
	 * @param string data to decode
	 * @return array decoded dictionary
	 */
	static private function decode_dictionary ( & $data ) {
		$dictionary = array();
		$previous = null;
		while ( ( $char = self::char( $data ) ) != 'e' ) {
			if ( $char === false )
				return self::set_error( new Exception( 'Unterminated dictionary' ) );
			if ( ! ctype_digit( $char ) )
				return self::set_error( new Exception( 'Invalid dictionary key' ) );
			$key = self::decode_string( $data );
			if ( isset( $dictionary[$key] ) )
				return self::set_error( new Exception( 'Duplicate dictionary key' ) );
			if ( $key < $previous )
				self::set_error( new Exception( 'Missorted dictionary key' ) );
			$dictionary[$key] = self::decode_data( $data );
			$previous = $key;
		}
		$data = substr( $data, 1 );
		return $dictionary;
	}

	/** Decode torrent list
	 * @param string data to decode
	 * @return array decoded list
	 */
	static private function decode_list ( & $data ) {
		$list = array();
		while ( ( $char = self::char( $data ) ) != 'e' ) {
			if ( $char === false )
				return self::set_error( new Exception( 'Unterminated list' ) );
			$list[] = self::decode_data( $data );
		}
		$data = substr( $data, 1 );
		return $list;
	}

	/** Decode torrent string
	 * @param string data to decode
	 * @return string decoded string
	 */
	static private function decode_string ( & $data ) {
		if ( self::char( $data ) === '0' && substr( $data, 1, 1 ) != ':' )
			self::set_error( new Exception( 'Invalid string length, leading zero' ) );
		if ( ! $colon = @strpos( $data, ':' ) )
			return self::set_error( new Exception( 'Invalid string length, colon not found' ) );
		$length = intval( substr( $data, 0, $colon ) );
		if ( $length + $colon + 1 > strlen( $data ) )
			return self::set_error( new Exception( 'Invalid string, input too short for string length' ) );
		$string = substr( $data, $colon + 1, $length );
		$data = substr( $data, $colon + $length + 1 );
		return $string;
	}

	/** Decode torrent integer
	 * @param string data to decode
	 * @return integer decoded integer
	 */
	static private function decode_integer ( & $data ) {
		$start = 0;
		$end   = strpos( $data, 'e');
		if ( $end === 0 )
			self::set_error( new Exception( 'Empty integer' ) );
		if ( self::char( $data ) == '-' )
			$start++;
		if ( substr( $data, $start, 1 ) == '0' && $end > $start + 1 )
			self::set_error( new Exception( 'Leading zero in integer' ) );
		if ( ! ctype_digit( substr( $data, $start, $start ? $end - 1 : $end ) ) )
			self::set_error( new Exception( 'Non-digit characters in integer' ) );
		$integer = substr( $data, 0, $end );
		$data    = substr( $data, $end + 1 );
		return 0 + $integer;
	}

	/**** Internal Helpers ****/

	/** Build torrent info
	 * @param string|array source folder/file(s) path
	 * @param integer piece length
	 * @return array|boolean torrent info or false if data isn't folder/file(s)
	 */
	protected function build ( $data, $piece_length ) {
		if ( is_null( $data ) )
			return false;
		elseif ( is_array( $data ) && self::is_list( $data ) )
			return $this->info = $this->files( $data, $piece_length );
		elseif ( is_dir( $data ) )
			return $this->info = $this->folder( $data, $piece_length );
		elseif ( ( is_file( $data ) || self::url_exists( $data ) ) && ! self::is_torrent( $data ) )
			return $this->info = $this->file( $data, $piece_length );
		else
			return false;
	}

	/** Set torrent creator and creation date
	 * @param any param
	 * @return any param
	 */
	protected function touch ( $void = null ) {
		$this->{'created by'}		= 'Torrent RW PHP Class - http://github.com/adriengibrat/torrent-rw';
		$this->{'creation date'}	= time();
		return $void;
	}

	/** Add an error to errors stack
	 * @param Exception error to add
	 * @param boolean return error message or not (optional, default to false)
	 * @return boolean|string return false or error message if requested
	 */
	static protected function set_error ( $exception, $message = false ) {
		return ( array_unshift( self::$_errors, $exception ) && $message ) ? $exception->getMessage() : false;
	}

	/** Build announce list
	 * @param string|array announce url / list
	 * @param string|array announce url / list to add (optionnal)
	 * @return array announce list (array of arrays)
	 */
	static protected function announce_list( $announce, $merge = array() ) {
		return array_map( create_function( '$a', 'return (array) $a;' ), array_merge( (array) $announce, (array) $merge ) );
	}

	/** Get the first announce url in a list
	 * @param array announce list (array of arrays if tiered trackers)
	 * @return string first announce url
	 */
	static protected function first_announce( $announce ) {
		while ( is_array( $announce ) )
			$announce = reset( $announce );
		return $announce;
	}

	/** Helper to pack data hash
	 * @param string data
	 * @return string packed data hash
	 */
	static protected function pack ( & $data ) {
		return pack('H*', sha1( $data ) ) . ( $data = null );
	}

	/** Helper to build file path
	 * @param array file path
	 * @param string base folder
	 * @return string real file path
	 */
	static protected function path ( $path, $folder ) {
		array_unshift( $path, $folder );
		return join( DIRECTORY_SEPARATOR, $path );
	}

	/** Helper to explode file path
	 * @param string file path
	 * @return array file path
	 */
	static protected function path_explode ( $path ) {
		return explode( DIRECTORY_SEPARATOR, $path );
	}

	/** Helper to test if an array is a list
	 * @param array array to test
	 * @return boolean is the array a list or not
	 */
	static protected function is_list ( $array ) {
		foreach ( array_keys( $array ) as $key )
			if ( ! is_int( $key ) )
				return false;
		return true;
	}

	/** Build pieces depending on piece length from a file handler
	 * @param ressource file handle
	 * @param integer piece length
	 * @param boolean is last piece
	 * @return string pieces
	 */
	private function pieces ( $handle, $piece_length, $last = true ) {
		static $piece, $length;
		if ( empty( $length ) )
			$length	= $piece_length;
		$pieces = null;
		while ( ! feof( $handle ) ) {
			if ( ( $length = strlen( $piece .= fread( $handle, $length ) ) ) == $piece_length )
				$pieces .= self::pack( $piece );
			elseif ( ( $length = $piece_length - $length ) < 0 )
				return self::set_error( new Exception( 'Invalid piece length!' ) );
		}
		fclose( $handle );
		return $pieces . ( $last && $piece ? self::pack( $piece ) : null);
	}

	/** Build torrent info from single file
	 * @param string file path
	 * @param integer piece length
	 * @return array torrent info
	 */
	private function file ( $file, $piece_length ) {
		if ( ! $handle = self::fopen( $file, $size = self::filesize( $file ) ) )
			return self::set_error( new Exception( 'Failed to open file: "' . $file . '"' ) );
		if ( self::is_url( $file ) )
			$this->url_list( $file );
		$path = self::path_explode( $file );
		return array(
			'length'	=> $size,
			'name'		=> end( $path ),
			'piece length'	=> $piece_length,
			'pieces'	=> $this->pieces( $handle, $piece_length )
		);
	}

	/** Build torrent info from files
	 * @param array file list
	 * @param integer piece length
	 * @return array torrent info
	 */
	private function files ( $files, $piece_length ) {
		sort( $files );
		usort( $files, create_function( '$a,$b', 'return strrpos($a,DIRECTORY_SEPARATOR)-strrpos($b,DIRECTORY_SEPARATOR);' ) );
		$first	= current( $files );
		if ( ! self::is_url( $first ) )
			$files = array_map( 'realpath', $files );
		else
			$this->url_list( dirname( $first ) . DIRECTORY_SEPARATOR );
		$files_path = array_map('self::path_explode', $files );
		$root = call_user_func_array('array_intersect_assoc' , $files_path);
		$pieces = null; $info_files = array(); $count = count( $files ) - 1;
		foreach ( $files as $i => $file ) {
			if ( ! $handle = self::fopen( $file, $filesize = self::filesize( $file ) ) ) {
				self::set_error( new Exception( 'Failed to open file: "' . $file . '" discarded' ) );
				continue;
			}
			$pieces .= $this->pieces( $handle, $piece_length, $count == $i );
			$info_files[] = array(
				'length'	=> $filesize,
				'path'		=> array_diff_assoc( $files_path[$i], $root )
			);
		}
		return array(
			'files'		=> $info_files,
			'name'		=> end( $root ),
			'piece length'	=> $piece_length,
			'pieces'	=> $pieces
		);

	}

	/** Build torrent info from folder content
	 * @param string folder path
	 * @param integer piece length
	 * @return array torrent info
	 */
	private function folder ( $dir, $piece_length ) {
		return $this->files( self::scandir( $dir ), $piece_length );
	}

	/** Helper to return the first char of encoded data
	 * @param string encoded data
	 * @return string|boolean first char of encoded data or false if empty data
	 */
	static private function char ( $data ) {
		return empty( $data ) ?
			false :
			substr( $data, 0, 1 );
	}

	/**** Public Helpers ****/

	/** Helper to format size in bytes to human readable
	 * @param integer size in bytes
	 * @param integer precision after coma
	 * @return string formated size in appropriate unit
	 */
	static public function format ( $size, $precision = 2 ) {
		$units = array ('octets', 'Ko', 'Mo', 'Go', 'To');
		while( ( $next = next( $units ) ) && $size > 1024 )
			$size /= 1024;
		return round( $size, $precision ) . ' ' . ( $next ? prev( $units ) : end( $units ) );
	}

	/** Helper to return filesize (even bigger than 2Gb -linux only- and distant files size)
	 * @param string file path
	 * @return double|boolean filesize or false if error
	 */
	static public function filesize ( $file ) {
		if ( is_file( $file ) )
			return (double) sprintf( '%u', @filesize( $file ) );
		else if ( $content_length = preg_grep( $pattern = '#^Content-Length:\s+(\d+)$#i', (array) @get_headers( $file ) ) )
			return (int) preg_replace( $pattern, '$1', reset( $content_length ) );
	}

	/** Helper to open file to read (even bigger than 2Gb, linux only)
	 * @param string file path
	 * @param integer|double file size (optional)
	 * @return resource|boolean file handle or false if error
	 */
	static public function fopen ( $file, $size = null ) {
		if ( ( is_null( $size ) ? self::filesize( $file ) : $size ) <= 2 * pow( 1024, 3 ) )
			return fopen( $file, 'r' );
		elseif ( PHP_OS != 'Linux' )
			return self::set_error( new Exception( 'File size is greater than 2GB. This is only supported under Linux' ) );
		elseif ( ! is_readable( $file ) )
			return false;
		else
			return popen( 'cat ' . escapeshellarg( realpath( $file ) ), 'r' );
	}

	/** Helper to scan directories files and sub directories recursively
	 * @param string directory path
	 * @return array directory content list
	 */
	static public function scandir ( $dir ) {
		$paths = array();
		foreach ( scandir( $dir ) as $item )
				if ( $item != '.' && $item != '..' )
					if ( is_dir( $path = realpath( $dir . DIRECTORY_SEPARATOR . $item ) ) )
						$paths = array_merge( self::scandir( $path ), $paths );
					else
						$paths[] = $path;
		return $paths;
	}

	/** Helper to check if string is an url (http)
	 * @param string url to check
	 * @return boolean is string an url
	 */
	static public function is_url ( $url ) {
		return preg_match( '#^http(s)?://[a-z0-9-]+(.[a-z0-9-]+)*(:[0-9]+)?(/.*)?$#i', $url );
	}

	/** Helper to check if url exists
	 * @param string url to check
	 * @return boolean does the url exist or not
	 */
	static public function url_exists ( $url ) {
		return self::is_url( $url ) ?
			(bool) self::filesize ( $url ) :
			false;
	}
	/** Helper to check if a file is a torrent
	 * @param string file location
	 * @param float http timeout (optional, default to self::timeout 30s)
	 * @return boolean is the file a torrent or not
	 */
	static public function is_torrent ( $file, $timeout = self::timeout ) {
		return ( $start = self::file_get_contents( $file, $timeout, 0, 11 ) )
			 && $start === 'd8:announce'
			 || $start === 'd10:created'
			 || $start === 'd13:creatio'
			 || $start === 'd13:announc'
			 || $start === 'd12:_info_l'
			 || substr($start, 0, 10) === 'd7:comment' // @see https://github.com/adriengibrat/torrent-rw/issues/32
			 || substr($start, 0, 7) === 'd4:info'
			 || substr($start, 0, 3) === 'd9:'; // @see https://github.com/adriengibrat/torrent-rw/pull/17
	}

	/** Helper to get (distant) file content
	 * @param string file location
	 * @param float http timeout (optional, default to self::timeout 30s)
	 * @param integer starting offset (optional, default to null)
	 * @param integer content length (optional, default to null)
	 * @return string|boolean file content or false if error
	 */
	static public function file_get_contents ( $file, $timeout = self::timeout, $offset = null, $length = null ) {
		if ( is_file( $file ) || ini_get( 'allow_url_fopen' ) ) {
			$context = ! is_file( $file ) && $timeout ? 
				stream_context_create( array( 'http' => array( 'timeout' => $timeout ) ) ) : 
				null;
			return ! is_null( $offset ) ? $length ?
				@file_get_contents( $file, false, $context, $offset, $length ) : 
				@file_get_contents( $file, false, $context, $offset ) : 
				@file_get_contents( $file, false, $context );
		} elseif ( ! function_exists( 'curl_init' ) )
			return self::set_error( new Exception( 'Install CURL or enable "allow_url_fopen"' ) );
		$handle = curl_init( $file );
		if ( $timeout )
			curl_setopt( $handle, CURLOPT_TIMEOUT, $timeout );
		if ( $offset || $length )
			curl_setopt( $handle, CURLOPT_RANGE, $offset . '-' . ( $length ? $offset + $length -1 : null ) );
		curl_setopt( $handle, CURLOPT_RETURNTRANSFER, 1 );
		$content = curl_exec( $handle );
		$size = curl_getinfo( $handle, CURLINFO_CONTENT_LENGTH_DOWNLOAD );
		curl_close( $handle );
		return ( $offset && $size == -1 ) || ( $length && $length != $size ) ? $length ?
			substr( $content, $offset, $length) :
			substr( $content, $offset) :
			$content;
	}

	/** Flatten announces list
	 * @param array announces list
	 * @return array flattened announces list
	 */
	static public function untier( $announces ) {
		$list = array();
		foreach ( (array) $announces as $tier ) {
			is_array( $tier ) ? 
				$list = array_merge( $list, self::untier( $tier ) ) :
				array_push( $list, $tier );
		}
		return $list;
	}

}
