""" Python 'utf-8-sig' Codec
This work similar to UTF-8 with the following changes:

* On encoding/writing a UTF-8 encoded BOM will be prepended/written as the
  first three bytes.

* On decoding/reading if the first three bytes are a UTF-8 encoded BOM, these
  bytes will be skipped.
"""
import codecs

### Codec APIs

def encode(input, errors='strict'):
    return (codecs.BOM_UTF8 + codecs.utf_8_encode(input, errors)[0], len(input))

def decode(input, errors='strict'):
    prefix = 0
    if input.startswith(codecs.BOM_UTF8):
        input = input[3:]
        prefix = 3
    (output, consumed) = codecs.utf_8_decode(input, errors, True)
    return (output, consumed+prefix)

class StreamWriter(codecs.StreamWriter):
    def reset(self):
        codecs.StreamWriter.reset(self)
        try:
            del self.encode
        except AttributeError:
            pass

    def encode(self, input, errors='strict'):
        self.encode = codecs.utf_8_encode
        return encode(input, errors)

class StreamReader(codecs.StreamReader):
    def reset(self):
        codecs.StreamReader.reset(self)
        try:
            del self.decode
        except AttributeError:
            pass

    def decode(self, input, errors='strict'):
        if len(input) < 3 and codecs.BOM_UTF8.startswith(input):
            # not enough data to decide if this is a BOM
            # => try again on the next call
            return (u"", 0)
        self.decode = codecs.utf_8_decode
        return decode(input, errors)

### encodings module API

def getregentry():

    return (encode,decode,StreamReader,StreamWriter)
