#
# Stolen from gavinandresen's django field validator
#  http://bitcointalk.org/index.php?topic=1026.0
#

import re
from hashlib import sha256
import math

__b58chars = '123456789ABCDEFGHJKLMNPQRSTUVWXYZabcdefghijkmnopqrstuvwxyz'
__b58base = len(__b58chars)

def b58encode(v):
  """ encode v, which is a little-endian string of bytes, to base58.    
  """

  long_value = 0L
  for (i, c) in enumerate(v[::-1]):
    long_value += (256**i) * ord(c)

  result = ''
  while long_value >= __b58base:
    div, mod = divmod(long_value, __b58base)
    result = __b58chars[mod] + result
    long_value = div
  result = __b58chars[long_value] + result

  # Pad front with Base58-encoded-0 for leading zeros:
  nPad = int((len(v)*8 / (math.log(58,2))) - len(result))

  return (__b58chars[0]*nPad) + result

def b58decode(v, length):
  """ decode v into a little-endian string of len bytes
  """
  long_value = 0L
  for (i, c) in enumerate(v[::-1]):
    long_value += __b58chars.find(c) * (__b58base**i)

  result = ''
  while long_value >= 256:
    div, mod = divmod(long_value, 256)
    result = chr(mod) + result
    long_value = div
  result = chr(long_value) + result
  if len(result) < length:
    n_pad = length-len(result)
    result = chr(0)*n_pad + result
  return result

def get_bcaddress_version(strAddress):
  """ Returns None if strAddress is invalid.  Otherwise returns integer version of address. """
  addr = b58decode(strAddress,25)
  version = addr[0]
  checksum = addr[-4:]
  vh160 = addr[:-4] # Version plus hash160 is what is checksummed
  h3=sha256(sha256(vh160).digest()).digest()
  if h3[0:4] == checksum:
    return ord(version)
  return None

def isvalid(value):
  value = value.strip()
  if re.match(r"[a-zA-Z1-9]{33,35}$", value) is None:
    return False
  return get_bcaddress_version(value) is not None