#!venv/bin/python
#
# This script is a very simple APRS-IS LoRa igate that
# runs on a raspberry pi and expects a RFM9x on the SPI bus.
#
# Also, there are two status LEDs on D23 and D24 that count
# the incoming messages.
#
# It is a send-only i-gate that uses the HTTP POST mechanism described
# on http://aprs-is.net/SendOnlyPorts.aspx
#
import datetime
import socket
import struct
import time

import busio
from digitalio import DigitalInOut, Direction, Pull
import board
# Import the RFM9x radio module.
import adafruit_rfm9x

# For APRS-IS
APRS_IS_SERVER = "france.aprs2.net"
APRS_IS_PORT = 8080
#APRS_IS_PORT = 14580
CALLSIGN = "HB9EGM-10"
PASSCODE = "22681"
REPORTING_DISTANCE = "10"

def decode_encoded_position_report(packet):
    """Returns a string with decoded latitude and longitude, or raises ValueError"""
    ix = packet.index(b":!/")
    gps_packet = packet[ix+3:]
    encoded_latitude = gps_packet[:4]
    encoded_longitude = gps_packet[4:8]

    (y1, y2, y3, y4) = struct.unpack("<bbbb", encoded_latitude)

    decodedLatitude = 90.0 - ((((y1-33) * pow(91,3)) + ((y2-33) * pow(91,2)) + ((y3-33) * 91) + y4-33) / 380926.0);

    (x1, x2, x3, x4) = struct.unpack("<bbbb", encoded_longitude)

    decodedLongitude = -180.0 + ((((x1-33) * pow(91,3)) + ((x2-33) * pow(91,2)) + ((x3-33) * 91) + x4-33) / 190463.0);
    return f"{decodedLatitude}N / {decodedLongitude}E"

def send_frame_to_aprs_is(frame):
    headers = { "Accept": "text/plain", "Content-Type": "application/octet-stream" }

    aprsauth = f"user {CALLSIGN} pass {PASSCODE} vers HB9EGM_lorapy 1.0 filter t/m/{CALLSIGN}/{REPORTING_DISTANCE}\n";

    # Prefix igate path
    path, _, message = frame[3:].partition(b":")
    new_frame = path + b",qAO," + CALLSIGN.encode() + b":" + message + b"\n"
    data = aprsauth.encode() + new_frame

    r = requests.post(f"http://{APRS_IS_SERVER}:{APRS_IS_PORT}/", data=data, headers=headers)
    print(f"{r.status_code} {r.content.decode()}")


led_yellow = DigitalInOut(board.D23)
led_yellow.direction = Direction.OUTPUT
led_green = DigitalInOut(board.D24)
led_green.direction = Direction.OUTPUT

led_counter = 0

def update_leds():
    led_counter = (led_counter + 1) % 4

    led_green.value = (led_counter & 0x1) != 0
    led_yellow.value = (led_counter & 0x2) != 0

update_leds()

cs = DigitalInOut(board.CE1)
reset = DigitalInOut(board.D25)
spi = busio.SPI(board.SCK, MOSI=board.MOSI, MISO=board.MISO)

baudrate = 5000000

# see https://docs.circuitpython.org/projects/rfm9x/en/latest/
try:
    rfm9x = adafruit_rfm9x.RFM9x(spi, cs, reset, 433.775, baudrate=baudrate, preamble_length=8)
    rfm9x.signal_bandwidth = 125000
    rfm9x.coding_rate = 5
    #rfm9x.tx_power = 23 # default 13

    rfm9x.spreading_factor = 12

    # Section 4.1.1.6 - Set low datarate automatically based on BW and SF
    symbolDuration = 1000 / ( rfm9x.signal_bandwidth / (1 << rfm9x.spreading_factor) )
    if symbolDuration > 16:
        rfm9x.low_datarate_optimize = 1
    else:
        rfm9x.low_datarate_optimize = 0

    print("Waiting for packets...")
    while True:
        packet = rfm9x.receive(timeout=4, with_header=True)
        if packet is not None:
            packet = bytes(packet) # otherwise it's a bytearray

            print("{}: {}".format(datetime.datetime.now(), packet))
            #print(" {}".format(" ".join(hex(x) for x in packet)))

            if b":!/" in packet:
                print(decode_encoded_position_report(packet))
                try:
                    send_frame_to_aprs_is(packet)
                except Exception as ex:
                    print("Error sending to APRS-IS")
                    print(ex)

            print(" RSSI: {}".format(rfm9x.last_rssi))
            print()

            update_leds()
except RuntimeError as error:
    print(f'RFM9x Error: {error}')