# bencode structured encoding
#
# Written by Petru Paler
#
# Permission is hereby granted, free of charge, to any person
# obtaining a copy of this software and associated documentation files
# (the "Software"), to deal in the Software without restriction,
# including without limitation the rights to use, copy, modify, merge,
# publish, distribute, sublicense, and/or sell copies of the Software,
# and to permit persons to whom the Software is furnished to do so,
# subject to the following conditions:
# 
# The above copyright notice and this permission notice shall be
# included in all copies or substantial portions of the Software.
# 
# The Software is provided "AS IS", without warranty of any kind,
# express or implied, including but not limited to the warranties of
# merchantability,  fitness for a particular purpose and
# noninfringement. In no event shall the  authors or copyright holders
# be liable for any claim, damages or other liability, whether in an
# action of contract, tort or otherwise, arising from, out of or in
# connection with the Software or the use or other dealings in the
# Software.

def decode_int(x, f):
    f += 1
    newf = x.index('e', f)
    try:
        n = int(x[f:newf])
    except (OverflowError, ValueError):
        n = long(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)
    try:
        n = int(x[f:colon])
    except (OverflowError, ValueError):
        n = long(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
    lastkey = None
    while x[f] != 'e':
        k, f = decode_string(x, f)
        if lastkey >= k:
            raise ValueError
        lastkey = k
        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):
        raise ValueError
    if l != len(x):
        raise ValueError
    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_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[type(Bencached(0))] = 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_int
except ImportError:
    pass

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