def truncate_sequence(
    sequence: list[int], truncate_at: int, end_token: int, add_ending: bool
) -> list[int]:

    if len(sequence) < truncate_at - 1:
        if add_ending:
            sequence.append(end_token)
        return sequence

    if len(sequence) < truncate_at:
        if add_ending:
            sequence[-1] = end_token
        return sequence

    TRUNCATED_SEQUENCE = sequence[:truncate_at]
    if add_ending:
        TRUNCATED_SEQUENCE[-1] = end_token

    return TRUNCATED_SEQUENCE


def pad_sequence(sequence: list[int], pad_until: int, pad_token: int) -> list[int]:

    if not (len(sequence) < pad_until):
        return sequence

    NUM_OF_PADDINGS = pad_until - len(sequence)
    PADDINGS = [pad_token] * NUM_OF_PADDINGS

    PADDED_SEQUENCE = sequence[:]
    PADDED_SEQUENCE.extend(PADDINGS)

    return PADDED_SEQUENCE

def create_padding_mask(sequence: list[int], pad_token: int) -> list[bool]:

    PADDING_MASK = [False] * len(sequence)

    for i in range(0, len(sequence)):

        if sequence[i] != pad_token:
            continue

        PADDING_MASK[i] = True

    return PADDING_MASK


def normalize_sequence(
    sequence: list[int],
    max_length: int,
    pad_token: int,
    end_token: int,
    add_ending: bool = True
) -> tuple[list[int], list[bool]]:
    new_sequence = truncate_sequence(sequence, max_length, end_token, add_ending)
    new_sequence = pad_sequence(new_sequence, max_length, pad_token)
    PADDING_MASK = create_padding_mask(new_sequence, pad_token)

    return (new_sequence, PADDING_MASK)