# The contents of this file are subject to the BitTorrent Open Source License
# Version 1.1 (the License). You may not copy or use this file, in either
# source code or executable form, except in compliance with the License. You
# may obtain a copy of the License at http://www.bittorrent.com/license/.
#
# Software distributed under the License is distributed on an AS IS basis,
# WITHOUT WARRANTY OF ANY KIND, either express or implied. See the License
# for the specific language governing rights and limitations under the
# License.

# Written by Petru Paler


def decode_int(x, f):
 f += 1
 newf = x.index('e', f)
 n = int(x[f:newf])
 if x[f] == '-':
 if x[f + 1] == '0':
 raise ValueError
 elif x[f] == '0' and newf != f+1:
 raise ValueError
 return (n, newf+1)

def decode_string(x, f):
 colon = x.index(':', f)
 n = int(x[f:colon])
 if x[f] == '0' and colon != f+1:
 raise ValueError
 colon += 1
 return (x[colon:colon+n], colon+n)

def decode_list(x, f):
 r, f = [], f+1
 while x[f] != 'e':
 v, f = decode_func[x[f]](x, f)
 r.append(v)
 return (r, f + 1)

def decode_dict(x, f):
 r, f = {}, f+1
 while x[f] != 'e':
 k, f = decode_string(x, f)
 r[k], f = decode_func[x[f]](x, f)
 return (r, f + 1)

decode_func = {}
decode_func['l'] = decode_list
decode_func['d'] = decode_dict
decode_func['i'] = decode_int
decode_func['0'] = decode_string
decode_func['1'] = decode_string
decode_func['2'] = decode_string
decode_func['3'] = decode_string
decode_func['4'] = decode_string
decode_func['5'] = decode_string
decode_func['6'] = decode_string
decode_func['7'] = decode_string
decode_func['8'] = decode_string
decode_func['9'] = decode_string

def bdecode(x):
 try:
 r, l = decode_func[x[0]](x, 0)
 except (IndexError, KeyError, ValueError):
 raise Exception("not a valid bencoded string")
 #if l != len(x):
 # raise Exception("invalid bencoded value (data after valid prefix)")
 return r

from types import StringType, IntType, LongType, DictType, ListType, TupleType


class Bencached(object):

 __slots__ = ['bencoded']

 def __init__(self, s):
 self.bencoded = s

def encode_bencached(x,r):
 r.append(x.bencoded)

def encode_int(x, r):
 r.extend(('i', str(x), 'e'))

def encode_bool(x, r):
 if x:
 encode_int(1, r)
 else:
 encode_int(0, r)
 
def encode_string(x, r):
 r.extend((str(len(x)), ':', x))

def encode_list(x, r):
 r.append('l')
 for i in x:
 encode_func[type(i)](i, r)
 r.append('e')

def encode_dict(x,r):
 r.append('d')
 ilist = x.items()
 ilist.sort()
 for k, v in ilist:
 r.extend((str(len(k)), ':', k))
 encode_func[type(v)](v, r)
 r.append('e')

encode_func = {}
encode_func[Bencached] = encode_bencached
encode_func[IntType] = encode_int
encode_func[LongType] = encode_int
encode_func[StringType] = encode_string
encode_func[ListType] = encode_list
encode_func[TupleType] = encode_list
encode_func[DictType] = encode_dict

try:
 from types import BooleanType
 encode_func[BooleanType] = encode_bool
except ImportError:
 pass

def bencode(x):
 r = []
 encode_func[type(x)](x, r)
 return ''.join(r)