""" Codec for the Punicode encoding, as specified in RFC 3492

Written by Martin v. Löwis.

"""

import codecs

##################### Encoding #####################################

def segregate(str):

    """3.1 Basic code point segregation"""

    base = bytearray()

    extended = set()

    for c in str:

        if ord(c) < 128:

            base.append(ord(c))

        else:

            extended.add(c)

    extended = sorted(extended)

    return bytes(base), extended

def selective_len(str, max):

    """Return the length of str, considering only characters below max."""

    res = 0

    for c in str:

        if ord(c) < max:

            res += 1

    return res

def selective_find(str, char, index, pos):

    """Return a pair (index, pos), indicating the next occurrence of

    char in str. index is the position of the character considering

    only ordinals up to and including char, and pos is the position in

    the full string. index/pos is the starting position in the full

    string."""

    l = len(str)

    while 1:

        pos += 1

        if pos == l:

            return (-1, -1)

        c = str[pos]

        if c == char:

            return index+1, pos

        elif c < char:

            index += 1

def insertion_unsort(str, extended):

    """3.2 Insertion unsort coding"""

    oldchar = 0x80

    result = []

    oldindex = -1

    for c in extended:

        index = pos = -1

        char = ord(c)

        curlen = selective_len(str, char)

        delta = (curlen+1) * (char - oldchar)

        while 1:

            index,pos = selective_find(str,c,index,pos)

            if index == -1:

                break

            delta += index - oldindex

            result.append(delta-1)

            oldindex = index

            delta = 0

        oldchar = char

    return result

def T(j, bias):

    # Punycode parameters: tmin = 1, tmax = 26, base = 36

    res = 36 * (j + 1) - bias

    if res < 1: return 1

    if res > 26: return 26

    return res

digits = b"abcdefghijklmnopqrstuvwxyz0123456789"

def generate_generalized_integer(N, bias):

    """3.3 Generalized variable-length integers"""

    result = bytearray()

    j = 0

    while 1:

        t = T(j, bias)

        if N < t:

            result.append(digits[N])

            return bytes(result)

        result.append(digits[t + ((N - t) % (36 - t))])

        N = (N - t) // (36 - t)

        j += 1

def adapt(delta, first, numchars):

    if first:

        delta //= 700

    else:

        delta //= 2

    delta += delta // numchars

    # ((base - tmin) * tmax) // 2 == 455

    divisions = 0

    while delta > 455:

        delta = delta // 35 # base - tmin

        divisions += 36

    bias = divisions + (36 * delta // (delta + 38))

    return bias

def generate_integers(baselen, deltas):

    """3.4 Bias adaptation"""

    # Punycode parameters: initial bias = 72, damp = 700, skew = 38

    result = bytearray()

    bias = 72

    for points, delta in enumerate(deltas):

        s = generate_generalized_integer(delta, bias)

        result.extend(s)

        bias = adapt(delta, points==0, baselen+points+1)

    return bytes(result)

def punycode_encode(text):

    base, extended = segregate(text)

    deltas = insertion_unsort(text, extended)

    extended = generate_integers(len(base), deltas)

    if base:

        return base + b"-" + extended

    return extended

##################### Decoding #####################################

def decode_generalized_number(extended, extpos, bias, errors):

    """3.3 Generalized variable-length integers"""

    result = 0

    w = 1

    j = 0

    while 1:

        try:

            char = ord(extended[extpos])

        except IndexError:

            if errors == "strict":

                raise UnicodeError("incomplete punicode string")

            return extpos + 1, None

        extpos += 1

        if 0x41 <= char <= 0x5A: # A-Z

            digit = char - 0x41

        elif 0x30 <= char <= 0x39:

            digit = char - 22 # 0x30-26

        elif errors == "strict":

            raise UnicodeError("Invalid extended code point '%s'"

                               % extended[extpos])

        else:

            return extpos, None

        t = T(j, bias)

        result += digit * w

        if digit < t:

            return extpos, result

        w = w * (36 - t)

        j += 1

def insertion_sort(base, extended, errors):

    """3.2 Insertion unsort coding"""

    char = 0x80

    pos = -1

    bias = 72

    extpos = 0

    while extpos < len(extended):

        newpos, delta = decode_generalized_number(extended, extpos,

                                                  bias, errors)

        if delta is None:

            # There was an error in decoding. We can't continue because

            # synchronization is lost.

            return base

        pos += delta+1

        char += pos // (len(base) + 1)

        if char > 0x10FFFF:

            if errors == "strict":

                raise UnicodeError("Invalid character U+%x" % char)

            char = ord('?')

        pos = pos % (len(base) + 1)

        base = base[:pos] + chr(char) + base[pos:]

        bias = adapt(delta, (extpos == 0), len(base))

        extpos = newpos

    return base

def punycode_decode(text, errors):

    if isinstance(text, str):

        text = text.encode("ascii")

    if isinstance(text, memoryview):

        text = bytes(text)

    pos = text.rfind(b"-")

    if pos == -1:

        base = ""

        extended = str(text, "ascii").upper()

    else:

        base = str(text[:pos], "ascii", errors)

        extended = str(text[pos+1:], "ascii").upper()

    return insertion_sort(base, extended, errors)

### Codec APIs

class Codec(codecs.Codec):

    def encode(self, input, errors='strict'):

        res = punycode_encode(input)

        return res, len(input)

    def decode(self, input, errors='strict'):

        if errors not in ('strict', 'replace', 'ignore'):

            raise UnicodeError("Unsupported error handling "+errors)

        res = punycode_decode(input, errors)

        return res, len(input)

class IncrementalEncoder(codecs.IncrementalEncoder):

    def encode(self, input, final=False):

        return punycode_encode(input)

class IncrementalDecoder(codecs.IncrementalDecoder):

    def decode(self, input, final=False):

        if self.errors not in ('strict', 'replace', 'ignore'):

            raise UnicodeError("Unsupported error handling "+self.errors)

        return punycode_decode(input, self.errors)

class StreamWriter(Codec,codecs.StreamWriter):

    pass

class StreamReader(Codec,codecs.StreamReader):

    pass

### encodings module API

def getregentry():

    return codecs.CodecInfo(

        name='punycode',

        encode=Codec().encode,

        decode=Codec().decode,

        incrementalencoder=IncrementalEncoder,

        incrementaldecoder=IncrementalDecoder,

        streamwriter=StreamWriter,

        streamreader=StreamReader,

    )