import numpy as np
import numpy.typing as npt

GEN_MATRIX = np.asarray([(1, 1, 1, 0, 0, 0, 0),
                         (1, 0, 0, 1, 1, 0, 0),
                         (0, 1, 0, 1, 0, 1, 0),
                         (1, 1, 0, 1, 0, 0, 1),
                         ])
PARITY_MATRIX = np.asarray([(0, 0, 0, 1, 1, 1, 1),
                            (0, 1, 1, 0, 0, 1, 1),
                            (1, 0, 1, 0, 1, 0, 1),
                            ])
DECODER_MATRIX = np.asarray([(0, 0, 1, 0, 0, 0, 0,),
                             (0, 0, 0, 0, 1, 0, 0,),
                             (0, 0, 0, 0, 0, 1, 0,),
                             (0, 0, 0, 0, 0, 0, 1,),
                             ])


def number_to_list(number: int, N: int) -> npt.NDArray:
    """Return the last N bits of a number as an MSB-first array"""
    return np.array([(number >> (N-1-i)) % 2 for i in range(0, N)],dtype=int)


def list_to_number(array: npt.NDArray, N: int) -> int:
    """Reconstruct a number from the first N elements of an MSB-first array"""
    output = 0
    for i in range(0, N):
        output += array[i] << (N-1-i)
    return output


def encode_nibble(data: int) -> int:
    """Encode the lower 4 bits of data as hamming(7,4)"""
    data_asarr = number_to_list(data, 4)
    output_asarr = (data_asarr @ GEN_MATRIX) % 2
    return list_to_number(output_asarr, 7)


def hamming_7_4_encode(data: list[int]) -> list[int]:
    """Encode a list of ints using Hamming(7,4)
       The returned list is twice as long as the list in the argument"""
    data_encoded = []
    for element in data:
        data_encoded += [encode_nibble(element >> 4),
                         encode_nibble(element % 16)]
    return data_encoded


def decode_nibble(data: int) -> int:
    """decode a single nibble using the parity check matrix of Hamming(7,4).
       This should correct 2 errors maximum."""
    data_asarr = number_to_list(data, 7)
    syndrome = (PARITY_MATRIX @ data_asarr) % 2
    error = list_to_number(syndrome, 3)
    if error == 0:
        data_decoded = (DECODER_MATRIX @ data_asarr) % 2
        return list_to_number(data_decoded, 4)
    data_asarr[error - 1] ^= 1
    data_decoded = (DECODER_MATRIX @ data_asarr) % 2
    return list_to_number(data_decoded, 4)


def hamming_7_4_decode(data: list[int]) -> list[int]:
    """Decode a list of ints using Hamming(7,4)
       The returned list is half as long as the list in the argument"""
    return [(decode_nibble(data[i]) << 4) + (decode_nibble(data[i + 1])) for i in range(0, len(data), 2)]


if __name__ == "__main__":
    msg = 'TEST DE HA5PLS'
    data_in = [byte for byte in bytearray(msg.encode())]
    data_encoded = hamming_7_4_encode(data_in)
    print(f"Data sent: {msg}")

    data_corrupted_1bit = [data ^ (1 << (idx % 7))
                           for idx, data in enumerate(data_encoded)]
    # print(f"Corrupt data with 1-bit errors: {data_corrupted_1bit}")
    data_corrected_1bit = hamming_7_4_decode(data_corrupted_1bit)
    data_corrected_1bit_str = [int.to_bytes(int(i), 1, "big").decode(
        encoding="utf-8", errors="ignore") for i in data_corrected_1bit]
    print(f"Recovered data from 1-bit errors: {data_corrected_1bit_str}")

    data_corrupted_2bit = [data ^ (5 << (idx % 7))
                           for idx, data in enumerate(data_encoded)]
    # print(f"Corrupt data with 2-bit errors: {data_corrupted_2bit}")
    data_corrected_2bit = hamming_7_4_decode(data_corrupted_2bit)
    data_corrected_2bit_str = [int.to_bytes(int(i), 1, "big").decode(
        encoding="utf-8", errors="ignore") for i in data_corrected_2bit]
    print(f"Recovered data from 2-bit errors: {data_corrected_2bit_str}")

    # print(f"Corrupt data with 3-bit errors: {data_corrupted_3bit}")
    data_corrected_noerr = hamming_7_4_decode(data_encoded)
    data_corrected_noerr_str = [int.to_bytes(int(i), 1, "big").decode(
        encoding="utf-8", errors="ignore") for i in data_corrected_noerr]
    print(f"Recovered data from no errors: {data_corrected_noerr_str}")