# Copyright 2020 Google LLC
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
#     https://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.

import array
import struct

from google_crc32c._checksum import CommonChecksum


def extend(crc, chunk):
    """Update an existing CRC checksum with new chunk of data.

    Args
        crc (int): An existing CRC check sum.
        chunk (Union[bytes, List[int], Tuple[int]]): A new chunk of data.
            Intended to be a byte string or similar.

    Returns
        int: New CRC checksum computed by extending existing CRC
        with ``chunk``.
    """
    c = Checksum()
    c._crc = crc
    c.update(chunk)
    return c._crc


def value(chunk):
    """Compute a CRC checksum for a chunk of data.

    Args
        chunk (Union[bytes, List[int], Tuple[int]]): A new chunk of data.
            Intended to be a byte string or similar.

    Returns
        int: New CRC checksum computed for ``chunk``.
    """
    c = Checksum()
    c.update(chunk)
    return c._crc


class Checksum(CommonChecksum):
    """Hashlib-alike helper for CRC32C operations.

    Args:
        initial_value (Optional[bytes]): the initial chunk of data from
            which the CRC32C checksum is computed.  Defaults to b''.
    """

    def __init__(self, initial_value=b""):
        self._crc = 0
        if initial_value != b"":
            self.update(initial_value)

    def update(self, data):
        """Update the checksum with a new chunk of data.

        Args:
            chunk (Optional[bytes]): a chunk of data used to extend
                the CRC32C checksum.
        """
        if type(data) != array.array or data.itemsize != 1:
            buffer = array.array("B", data)
        else:
            buffer = data
        self._crc = self._crc ^ 0xFFFFFFFF
        for b in buffer:
            table_poly = _TABLE[(b ^ self._crc) & 0xFF]
            self._crc = table_poly ^ ((self._crc >> 8) & 0xFFFFFFFF)
        self._crc = self._crc ^ 0xFFFFFFFF


# fmt:off
_TABLE = [
    0x00000000, 0xf26b8303, 0xe13b70f7, 0x1350f3f4, 0xc79a971f, 0x35f1141c, 0x26a1e7e8,
    0xd4ca64eb, 0x8ad958cf, 0x78b2dbcc, 0x6be22838, 0x9989ab3b, 0x4d43cfd0, 0xbf284cd3,
    0xac78bf27, 0x5e133c24, 0x105ec76f, 0xe235446c, 0xf165b798, 0x30e349b, 0xd7c45070,
    0x25afd373, 0x36ff2087, 0xc494a384, 0x9a879fa0, 0x68ec1ca3, 0x7bbcef57, 0x89d76c54,
    0x5d1d08bf, 0xaf768bbc, 0xbc267848, 0x4e4dfb4b, 0x20bd8ede, 0xd2d60ddd, 0xc186fe29,
    0x33ed7d2a, 0xe72719c1, 0x154c9ac2, 0x61c6936, 0xf477ea35, 0xaa64d611, 0x580f5512,
    0x4b5fa6e6, 0xb93425e5, 0x6dfe410e, 0x9f95c20d, 0x8cc531f9, 0x7eaeb2fa, 0x30e349b1,
    0xc288cab2, 0xd1d83946, 0x23b3ba45, 0xf779deae, 0x5125dad, 0x1642ae59, 0xe4292d5a,
    0xba3a117e, 0x4851927d, 0x5b016189, 0xa96ae28a, 0x7da08661, 0x8fcb0562, 0x9c9bf696,
    0x6ef07595, 0x417b1dbc, 0xb3109ebf, 0xa0406d4b, 0x522bee48, 0x86e18aa3, 0x748a09a0,
    0x67dafa54, 0x95b17957, 0xcba24573, 0x39c9c670, 0x2a993584, 0xd8f2b687, 0xc38d26c,
    0xfe53516f, 0xed03a29b, 0x1f682198, 0x5125dad3, 0xa34e59d0, 0xb01eaa24, 0x42752927,
    0x96bf4dcc, 0x64d4cecf, 0x77843d3b, 0x85efbe38, 0xdbfc821c, 0x2997011f, 0x3ac7f2eb,
    0xc8ac71e8, 0x1c661503, 0xee0d9600, 0xfd5d65f4, 0xf36e6f7, 0x61c69362, 0x93ad1061,
    0x80fde395, 0x72966096, 0xa65c047d, 0x5437877e, 0x4767748a, 0xb50cf789, 0xeb1fcbad,
    0x197448ae, 0xa24bb5a, 0xf84f3859, 0x2c855cb2, 0xdeeedfb1, 0xcdbe2c45, 0x3fd5af46,
    0x7198540d, 0x83f3d70e, 0x90a324fa, 0x62c8a7f9, 0xb602c312, 0x44694011, 0x5739b3e5,
    0xa55230e6, 0xfb410cc2, 0x92a8fc1, 0x1a7a7c35, 0xe811ff36, 0x3cdb9bdd, 0xceb018de,
    0xdde0eb2a, 0x2f8b6829, 0x82f63b78, 0x709db87b, 0x63cd4b8f, 0x91a6c88c, 0x456cac67,
    0xb7072f64, 0xa457dc90, 0x563c5f93, 0x82f63b7, 0xfa44e0b4, 0xe9141340, 0x1b7f9043,
    0xcfb5f4a8, 0x3dde77ab, 0x2e8e845f, 0xdce5075c, 0x92a8fc17, 0x60c37f14, 0x73938ce0,
    0x81f80fe3, 0x55326b08, 0xa759e80b, 0xb4091bff, 0x466298fc, 0x1871a4d8, 0xea1a27db,
    0xf94ad42f, 0xb21572c, 0xdfeb33c7, 0x2d80b0c4, 0x3ed04330, 0xccbbc033, 0xa24bb5a6,
    0x502036a5, 0x4370c551, 0xb11b4652, 0x65d122b9, 0x97baa1ba, 0x84ea524e, 0x7681d14d,
    0x2892ed69, 0xdaf96e6a, 0xc9a99d9e, 0x3bc21e9d, 0xef087a76, 0x1d63f975, 0xe330a81,
    0xfc588982, 0xb21572c9, 0x407ef1ca, 0x532e023e, 0xa145813d, 0x758fe5d6, 0x87e466d5,
    0x94b49521, 0x66df1622, 0x38cc2a06, 0xcaa7a905, 0xd9f75af1, 0x2b9cd9f2, 0xff56bd19,
    0xd3d3e1a, 0x1e6dcdee, 0xec064eed, 0xc38d26c4, 0x31e6a5c7, 0x22b65633, 0xd0ddd530,
    0x417b1db, 0xf67c32d8, 0xe52cc12c, 0x1747422f, 0x49547e0b, 0xbb3ffd08, 0xa86f0efc,
    0x5a048dff, 0x8ecee914, 0x7ca56a17, 0x6ff599e3, 0x9d9e1ae0, 0xd3d3e1ab, 0x21b862a8,
    0x32e8915c, 0xc083125f, 0x144976b4, 0xe622f5b7, 0xf5720643, 0x7198540, 0x590ab964,
    0xab613a67, 0xb831c993, 0x4a5a4a90, 0x9e902e7b, 0x6cfbad78, 0x7fab5e8c, 0x8dc0dd8f,
    0xe330a81a, 0x115b2b19, 0x20bd8ed, 0xf0605bee, 0x24aa3f05, 0xd6c1bc06, 0xc5914ff2,
    0x37faccf1, 0x69e9f0d5, 0x9b8273d6, 0x88d28022, 0x7ab90321, 0xae7367ca, 0x5c18e4c9,
    0x4f48173d, 0xbd23943e, 0xf36e6f75, 0x105ec76, 0x12551f82, 0xe03e9c81, 0x34f4f86a,
    0xc69f7b69, 0xd5cf889d, 0x27a40b9e, 0x79b737ba, 0x8bdcb4b9, 0x988c474d, 0x6ae7c44e,
    0xbe2da0a5, 0x4c4623a6, 0x5f16d052, 0xad7d5351
]