#!/usr/bin/python
import sys
import socket

KISS_FEND = 0xC0    # Frame start/end marker
KISS_FESC = 0xDB    # Escape character
KISS_TFEND = 0xDC   # If after an escape, means there was an 0xC0 in the source message
KISS_TFESC = 0xDD   # If after an escape, means there was an 0xDB in the source message

if len(sys.argv) != 4:
    print "Usage: %s <source callsign> <destination callsign> <message>" % sys.argv[0]
    sys.exit(1)

# Addresses must be 6 bytes plus the SSID byte, each character shifted left by 1
# If it's the final address in the header, set the low bit to 1
# Ignoring command/response for simple example
def encode_address(s, final):
    if "-" not in s:
        s = s + "-0"    # default to SSID 0
    call, ssid = s.split('-')
    if len(call) < 6:
        call = call + " "*(6 - len(call)) # pad with spaces
    encoded_call = [ord(x) << 1 for x in call[0:6]]
    encoded_ssid = (int(ssid) << 1) | 0b01100000 | (0b00000001 if final else 0)
    return encoded_call + [encoded_ssid]

# Make a UI frame by concatenating the parts together
# This is just an array of ints representing bytes at this point
dest_addr = encode_address(sys.argv[2].upper(), False)
src_addr = encode_address(sys.argv[1].upper(), True)
c_byte = [0x03]           # This is a UI frame
pid = [0xF0]              # No protocol
msg = [ord(c) for c in sys.argv[3]]
packet = dest_addr + src_addr + c_byte + pid + msg

# Escape the packet in case either KISS_FEND or KISS_FESC ended up in our stream
packet_escaped = []
for x in packet:
    if x == KISS_FEND:
        packet_escaped += [KISS_FESC, KISS_TFEND]
    elif x == KISS_FESC:
        packet_escaped += [KISS_FESC, KISS_TFESC]
    else:
        packet_escaped += [x]

# Build the frame that we will send to Dire Wolf and turn it into a string
kiss_cmd = 0x00 # Two nybbles combined - TNC 0, command 0 (send data)
kiss_frame = [KISS_FEND, kiss_cmd] + packet_escaped + [KISS_FEND]
output = str(bytearray(kiss_frame))

# Connect to Dire Wolf listening on port 8001 on this machine and send the frame
s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
s.connect(("127.0.0.1", 8001))
s.send(output)
s.close()