#!/usr/bin/env python

from __future__ import with_statement
import sys
import urllib
import hashlib
from BitTorrent import bencode

if not sys.argv[1:]:
    raise SystemExit('Usage: %s filename.torrent' % sys.argv[0])

with open(sys.argv[1]) as datafile:
    data = bencode.bdecode(datafile.read())
    info_hash = hashlib.sha1(bencode.bencode(data['info']))
    magnet = 'magnet:?xt=urn:btih:%(hash)s&dn=%(name)s' % {
        'hash': info_hash.hexdigest(),
        'name': urllib.quote_plus(data['info']['name']),
    }
    try:
        if 'length' in data['info']:
            length = data['info']['length']
        else:
            length = sum(i['length'] for i in data['info']['files'])
        magnet += '&xl=%i' % length
    except KeyError: pass
    print magnet