from easybits import Bits
import codecs

def encode(text):
    "An encoder which only handles ASCII: non-ASCII characters are replaced with '?'. "
    "this will remove the most common characters in english texts [e, t, a, o, i, n, s, h] and by writing a 1 and followed by 3 bits"
    "other charcaters will be written with stadard 8 bit code"
    "this ecoding has about a 77 percent compression rate"
    "there is some loss in quality since unknown characters are replaced with ? and not decoded"
   
    result = Bits()
    commonchars = ['e', 't', 'a', 'o', 'i', 'n', 's', 'h']
    for char in text:
        try:
            b = Bits(char, encoding='ascii')
        except UnicodeEncodeError:
            b = Bits('?', encoding='ascii')
            char = '?'
        if char in commonchars:
            result = result.concat(Bits('1'))
            i = commonchars.index(char)
            if i == 0: 
                result = result.concat(Bits('000'))
            elif i == 1: 
                result = result.concat(Bits("001"))
            elif i == 2: 
                result = result.concat(Bits("010"))
            elif i == 3: 
                result = result.concat(Bits("011"))
            elif i == 4: 
                result = result.concat(Bits("100"))
            elif i == 5: 
                result = result.concat(Bits("101"))
            elif i == 6: 
                result = result.concat(Bits("110"))
            elif i == 7: 
                result = result.concat(Bits("111"))
        else:
            result = result.concat(b)
    return result.bytes

def decode(data):
    "Matching decoder. Checks if first bit is 1 or 0. If it is 1, then it changes character out of encoded form, which is 3 bits long. "
    "If not, it just converts it using standard ascii which is 8 bits."
    bits = Bits(bytes(data))
    text = ""
    commonchars = ['e', 't', 'a', 'o', 'i', 'n', 's', 'h']
    i = 0
    while i < len(bits):
        if bits[i] == 1:
            byte = bits[i+1:i+4]
            if byte == Bits('000'):
                text += commonchars[0]
            elif byte == Bits('001'):
                text += commonchars[1]
            elif byte == Bits('010'):
                text += commonchars[2]
            elif byte == Bits('011'):
                text += commonchars[3]
            elif byte == Bits('100'):
                text += commonchars[4]
            elif byte == Bits('101'):
                text += commonchars[5]
            elif byte == Bits('110'):
                text += commonchars[6]
            elif byte == Bits('111'):
                text += commonchars[7]
            i += 4
        
        else:
            b = bits[i:i+8]
            text += b.ascii
            i += 8
    
    return text

def register_codec(encode, decode, name):
    """Registers a codec so that it can later be used to encode
    or decode strings and bytes.
    """
    def encode_wrapper(text):
        return encode(text), len(text)

    def decode_wrapper(data):
        return decode(data), len(data)

    def search_for_codec(query):
        if query == name:
            return codecs.CodecInfo(encode_wrapper, decode_wrapper, name=name)

    codecs.register(search_for_codec)

register_codec(encode, decode, "commonchars")