horusdemodlib/horusdemodlib/encoder.py

#!/usr/bin/env python3
#
#   HorusDemodLib - Encoder helper functions
#
import ctypes
from ctypes import *
import codecs
import datetime
import logging
import sys
from enum import Enum
import os
import logging
from .decoder import decode_packet, hex_to_bytes


class Encoder():
    """
    Horus Binary Encoder class.

    Allows creation of a Horus Binary packet.

    """

    def __init__(
        self,
        libpath=f"",
    ):
        """
        Parameters
        ----------
        libpath : str
            Path to libhorus
        """

        if sys.platform == "darwin":
            libpath = os.path.join(libpath, "libhorus.dylib")
        elif sys.platform == "win32":
            libpath = os.path.join(libpath, "libhorus.dll")
        else:
            libpath = os.path.join(libpath, "libhorus.so")

        # future improvement would be to try a few places / names
        self.c_lib = ctypes.cdll.LoadLibrary(libpath)


        # Encoder/decoder functions
        self.c_lib.horus_l2_get_num_tx_data_bytes.restype = c_int

        self.c_lib.horus_l2_encode_tx_packet.restype = c_int
        # self.c_lib.horus_l2_encode_tx_packet.argtype = [
        #     POINTER(c_ubyte),
        #     c_ubyte * 
        #     POINTER(c_ubyte),
        #     c_int
        # ]

        self.c_lib.horus_l2_decode_rx_packet.argtype = [
            POINTER(c_ubyte),
            POINTER(c_ubyte),
            c_int
        ]

        self.c_lib.horus_l2_gen_crc16.restype = c_ushort
        self.c_lib.horus_l2_gen_crc16.argtype = [
            POINTER(c_ubyte),
            c_uint8
        ]

        # Init 
        self.c_lib.horus_l2_init()

    # in case someone wanted to use `with` style. I'm not sure if closing the modem does a lot.
    def __enter__(self):
        return self

    def __exit__(self, *a):
        self.close()

    def close(self) -> None:
        """
        Closes Horus modem. Does nothing here.
        """
        pass

    # Wrappers for libhorus C functions that we need.

    def get_num_tx_data_bytes(self, packet_size) -> int:
        """
        Calculate the number of transmit data bytes (uw+packet+fec) for a given
        input packet size.
        """
        return int(self.c_lib.horus_l2_get_num_tx_data_bytes(int(packet_size)))


    def horus_l2_encode_packet(self, packet):
        """
        Encode a packet using the Horus Binary FEC scheme, which:
        - Generates Golay (23,12) FEC for the packet
        - Adds this onto the packet contents, and interleaves/scrambles
        - Adds a unique word (0x2424) to the start.

        Packet input must be provided as bytes.
        """

        if type(packet) != bytes:
            raise TypeError("Input to encode_packet must be bytes!")

        _unencoded = c_ubyte * len(packet)
        _unencoded = _unencoded.from_buffer_copy(packet)
        _num_encoded_bytes = self.get_num_tx_data_bytes(len(packet))
        _encoded = c_ubyte * _num_encoded_bytes
        _encoded = _encoded()

        self.c_lib.horus_l2_encode_tx_packet.argtype = [
            c_ubyte * _num_encoded_bytes,
            c_ubyte * len(packet),
            c_int
        ]

        _num_bytes = int(self.c_lib.horus_l2_encode_tx_packet(_encoded, _unencoded, int(len(packet))))

        return (bytes(_encoded), _num_bytes)


    def horus_l2_decode_packet(self, packet, num_payload_bytes):
        """
        Decode a Horus-Binary encoded data packet.

        The packet must be provided as bytes, and must have the 2-byte unique word (0x2424)
        at the start.

        The expected number of output bytes must also be provided (22 or 32 for Horus v1 / v2 respectively)
        """

        if type(packet) != bytes:
            raise TypeError("Input to encode_packet must be bytes!")
        _encoded = c_ubyte * len(packet)
        _encoded = _encoded.from_buffer_copy(packet)
        _decoded = c_ubyte * num_payload_bytes
        _decoded = _decoded()

        self.c_lib.horus_l2_encode_tx_packet.argtype = [
            c_ubyte * num_payload_bytes,
            c_ubyte * len(packet),
            c_int
        ]

        self.c_lib.horus_l2_decode_rx_packet(_decoded, _encoded, num_payload_bytes)

        return bytes(_decoded)
    

    def create_horus_v2_packet(self,
            payload_id = 256,
            sequence_number = 0,
            time_dt = datetime.datetime.utcnow(),
            latitude = 0.0,
            longitude = 0.0,
            altitude = 0.0,
            speed = 0.0,
            satellites = 0,
            temperature = 0.0,
            battery_voltage = 0.0,
            # Default fields used for the 'custom' section of the packet.
            ascent_rate = 0.0,
            ext_temperature = 0.0,
            ext_humidity = 0.0,
            ext_pressure = 0.0,
            # Alternate custom data - must be bytes, and length=9
            custom_data = None
        ):
        pass

        # Sanity check input data.
        if payload_id < 256 or payload_id > 65535:
            raise ValueError("Invalid Horus v2 Payload ID. (Must be 256-65535)")
        
        # Clip sequence number
        sequence_number = int(sequence_number) % 65536

        # Try and extract HHMMSS from time
        try:
            hours = int(time_dt.hour)
            minutes = int(time_dt.minute)
            seconds = int(time_dt.second)
        except:
            raise ValueError("Could not parse input datetime object.")
        
        # Assume lat/lon are fine. They are just sent as floats anyway.

        # Clip Altitude
        altitude = int(altitude)
        if altitude < 0:
            altitude = 0
        if altitude > 65535:
            altitude = 65535
        
        # Clip Speed (kph)
        speed = int(speed)
        if speed < 0:
            speed = 0
        if speed > 255:
            speed = 255

        # Clip sats
        satellites = int(satellites)
        if satellites < 0:
            satellites = 0
        if satellites > 255:
            satellites = 255
        
        # Temperature

        # Battery voltage clip and conversion



        # Custom data

        # Ascent rate

        # PTU data


        # 'struct': '<HH3sffHBBbB9sH',
        # 'checksum': 'crc16',
        # 'fields': [
        #     ['payload_id', 'payload_id'],
        #     ['sequence_number', 'none'],
        #     ['time', 'time_hms'],
        #     ['latitude', 'degree_float'],
        #     ['longitude', 'degree_float'],
        #     ['altitude', 'none'],
        #     ['speed', 'none'],
        #     ['satellites', 'none'],
        #     ['temperature', 'none'],
        #     ['battery_voltage', 'battery_5v_byte'],
        #     ['custom', 'custom'],
        #     ['checksum', 'none']
        # ]
        


if __name__ == "__main__":
    import sys

    e = Encoder()

    # Check of get_num_tx_data_bytes
    print(f"Horus v1: 22 bytes in, {e.get_num_tx_data_bytes(22)} bytes out.")
    print(f"Horus v2: 32 bytes in, {e.get_num_tx_data_bytes(32)} bytes out.")

    print("Encoder Tests: ")
    horus_v1_unencoded = "000900071E2A000000000000000000000000259A6B14"
    horus_v1_unencoded = "e701010000000000000000000000000000000022020000000000000000006e8e"
    print(f"  Horus v1 Input:  {horus_v1_unencoded}")
    horus_v1_unencoded_bytes = codecs.decode(horus_v1_unencoded, 'hex')
    (_encoded, _num_bytes) = e.horus_l2_encode_packet(horus_v1_unencoded_bytes)
    print(f"  Horus v1 Output: {codecs.encode(_encoded, 'hex').decode().upper()}")


    print("Decoder Tests:")
    horus_v1_encoded = "2424C06B300D0415C5DBD332EFD7C190D7AF7F3C2891DE9F4BA1EB2B437BE1E2D8419D3DC9E44FDF78DAA07A98"
    print(f"  Horus v1 Input:  {horus_v1_encoded}")
    horus_v1_encoded_bytes = codecs.decode(horus_v1_encoded, 'hex')
    _decoded = e.horus_l2_decode_packet(horus_v1_encoded_bytes, 22)
    print(f"  Horus v1 Output: {codecs.encode(_decoded, 'hex').decode().upper()}")