from datetime import datetime

# Time begins in 2013
borealis_epoch = 1357023600

# Every modem IMEI shares this TAC
iridium_tac = '30023406'


def encode_uid(date: datetime, imei: str) -> int:
    """
    Encode a flight date and IMEI into a decodeable UID

    :param date: The start date of the flight
    :param imei: The IMEI of the modem
    :return: A flight UID

    Borealis Snowflake
    ------------------
    The UID is a snowflake in the structure:

                       Date                            IMEI
     111111111111111111111111111111111111111  111111111111111111111111
    63                                       23                      0

    +======+=========+==============================+================================+
    | Data | Bits    | Description                  | Obtaining                      |
    +======+=========+==============================+================================+
    | Date | 63 - 24 | Seconds since Borealis Epoch | (snowflake >> 24) + 1357023600 |
    +------+---------+------------------------------+--------------------------------+
    | IMEI | 23 - 0  | Last 7 digits of IMEI        | snowflake & 0x7ffffff          |
    +------+---------+------------------------------+--------------------------------+
    """
    time = int(date.timestamp()) - borealis_epoch
    snr = int(imei[8:])
    return (time << 24) | snr


def extract_date(uid: int) -> datetime:
    return datetime.fromtimestamp((uid >> 24) + borealis_epoch)


def extract_imei(uid: int) -> str:
    return iridium_tac + str(uid & 0x7ffffff).zfill(7)