# An iolist is one of
#  - None
#  - a list of iolists
#  - a CountedIOList
#  - a bytes
#  - a number i, 0 <= i < 256

class CountedIOList:
    def __init__(self, i):
        self.value = i
        self.length = len(i)

def counted(i):
    if isinstance(i, CountedIOList): return i
    return CountedIOList(i)

def withbyte(i, b):
    if i is None:
        return b
    elif isinstance(i, list):
        i.append(b)
        return i
    else:
        return [i, b]

_len = len

def join(*iolists):
    if _len(iolists) == 0:
        return None
    if _len(iolists) == 1:
        return iolists[0]
    return list(iolists)

def len(i):
    if i is None:
        return 0
    if isinstance(i, int):
        return 1
    if isinstance(i, _bytes):
        return _len(i)
    if isinstance(i, list):
        acc = 0
        for j in i:
            acc = acc + len(j)
        return acc
    if isinstance(i, CountedIOList):
        return i.length
    raise ValueError('invalid iolist: ' + repr(i) + ' ' + repr(type(i)))

_bytes = bytes

def bytes(i):
    buffer = bytearray(len(i))
    def fill(i, offset):
        while isinstance(i, CountedIOList):
            i = i.value
        if i is None:
            return offset
        if isinstance(i, int):
            buffer[offset] = i
            return offset + 1
        if isinstance(i, _bytes):
            buffer[offset:offset+_len(i)] = i
            return offset + _len(i)
        if isinstance(i, list):
            for j in i:
                offset = fill(j, offset)
            return offset
        raise ValueError('invalid iolist')
    fill(i, 0)
    return _bytes(buffer)