# Copyright (c) 2017 Pieter Wuille
#
# Permission is hereby granted, free of charge, to any person obtaining a copy
# of this software and associated documentation files (the "Software"), to deal
# in the Software without restriction, including without limitation the rights
# to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
# copies of the Software, and to permit persons to whom the Software is
# furnished to do so, subject to the following conditions:
#
# The above copyright notice and this permission notice shall be included in
# all copies or substantial portions of the Software.
#
# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
# IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
# FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
# AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
# LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
# OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
# THE SOFTWARE.

"""Reference implementation for Bech32 and segwit addresses."""
from .misc import const

CHARSET = "qpzry9x8gf2tvdw0s3jn54khce6mua7l"
BECH32_CONST = const(1)
BECH32M_CONST = const(0x2BC830A3)


class Encoding:
    """Enumeration type to list the various supported encodings."""

    BECH32 = 1
    BECH32M = 2


def bech32_polymod(values):
    """Internal function that computes the Bech32 checksum."""
    generator = [0x3B6A57B2, 0x26508E6D, 0x1EA119FA, 0x3D4233DD, 0x2A1462B3]
    chk = 1
    for value in values:
        top = chk >> 25
        chk = (chk & 0x1FFFFFF) << 5 ^ value
        for i in range(5):
            chk ^= generator[i] if ((top >> i) & 1) else 0
    return chk


def bech32_hrp_expand(hrp: str):
    """Expand the HRP into values for checksum computation."""
    return [ord(x) >> 5 for x in hrp] + [0] + [ord(x) & 31 for x in hrp]


def bech32_verify_checksum(hrp, data):
    """Verify a checksum given HRP and converted data characters."""
    check = bech32_polymod(bech32_hrp_expand(hrp) + data)
    if check == BECH32_CONST:
        return Encoding.BECH32
    elif check == BECH32M_CONST:
        return Encoding.BECH32M
    else:
        return None


def bech32_create_checksum(encoding, hrp, data):
    """Compute the checksum values given HRP and data."""
    values = bech32_hrp_expand(hrp) + data
    const = BECH32M_CONST if encoding == Encoding.BECH32M else BECH32_CONST
    polymod = bech32_polymod(values + [0, 0, 0, 0, 0, 0]) ^ const
    return [(polymod >> 5 * (5 - i)) & 31 for i in range(6)]


def bech32_encode(encoding, hrp, data):
    """Compute a Bech32 or Bech32m string given HRP and data values."""
    combined = data + bech32_create_checksum(encoding, hrp, data)
    return hrp + "1" + "".join([CHARSET[d] for d in combined])


def bech32_decode(bech):
    """Validate a Bech32/Bech32m string, and determine HRP and data."""
    if (any(ord(x) < 33 or ord(x) > 126 for x in bech)) or (
        bech.lower() != bech and bech.upper() != bech
    ):
        return (None, None, None)
    bech = bech.lower()
    pos = bech.rfind("1")
    if pos < 1 or pos + 7 > len(bech) or len(bech) > 90:
        return (None, None, None)
    if not all(x in CHARSET for x in bech[pos + 1 :]):
        return (None, None, None)
    hrp = bech[:pos]
    data = [CHARSET.find(x) for x in bech[pos + 1 :]]
    encoding = bech32_verify_checksum(hrp, data)
    if encoding is None:
        return (None, None, None)
    return (encoding, hrp, data[:-6])


def convertbits(data, frombits, tobits, pad=True):
    """General power-of-2 base conversion."""
    acc = 0
    bits = 0
    ret = []
    maxv = (1 << tobits) - 1
    max_acc = (1 << (frombits + tobits - 1)) - 1
    for value in data:
        if value < 0 or (value >> frombits):
            return None
        acc = ((acc << frombits) | value) & max_acc
        bits += frombits
        while bits >= tobits:
            bits -= tobits
            ret.append((acc >> bits) & maxv)
    if pad:
        if bits:
            ret.append((acc << (tobits - bits)) & maxv)
    elif bits >= frombits or ((acc << (tobits - bits)) & maxv):
        return None
    return ret


def decode(hrp, addr):
    """Decode a segwit address."""
    encoding, hrpgot, data = bech32_decode(addr)
    if hrpgot != hrp:
        return (None, None)
    decoded = convertbits(data[1:], 5, 8, False)
    if decoded is None or len(decoded) < 2 or len(decoded) > 40:
        return (None, None)
    if data[0] > 16:
        return (None, None)
    if data[0] == 0 and len(decoded) != 20 and len(decoded) != 32:
        return (None, None)
    if (data[0] == 0 and encoding != Encoding.BECH32) or (
        data[0] != 0 and encoding != Encoding.BECH32M
    ):
        return (None, None)
    return (data[0], decoded)


def encode(hrp, witver, witprog):
    """Encode a segwit address."""
    encoding = Encoding.BECH32 if witver == 0 else Encoding.BECH32M
    ret = bech32_encode(encoding, hrp, [witver] + convertbits(witprog, 8, 5))
    if decode(hrp, ret) == (None, None):
        return None
    return ret