"""Pretend to be a Micromate on a serial port: log what arrives, reply to POLL.

Proves the modem's return path (serial -> TCP) independently of the real unit.
"""
import os, select, sys, termios, time

path, baud = sys.argv[1], int(sys.argv[2]) if len(sys.argv) > 2 else 115200
B = {9600: termios.B9600, 38400: termios.B38400, 115200: termios.B115200}[baud]
fd = os.open(path, os.O_RDWR | os.O_NOCTTY | os.O_NONBLOCK)
a = termios.tcgetattr(fd)
a[0] = a[1] = a[3] = 0
a[2] = termios.CS8 | termios.CREAD | termios.CLOCAL
a[4] = a[5] = B
a[6] = list(a[6]); a[6][termios.VMIN] = 0; a[6][termios.VTIME] = 0
termios.tcsetattr(fd, termios.TCSANOW, a)
termios.tcflush(fd, termios.TCIOFLUSH)

# A real POLL probe reply, captured from UM12947 on 2026-09-24.
REPLY = bytes.fromhex("0200c5a4000000000000300000000000000099") + b"\x03"

print(f"fake unit on {path} @ {baud}; will answer any inbound frame", flush=True)
while True:
    r, _, _ = select.select([fd], [], [], 1.0)
    if not r:
        continue
    data = os.read(fd, 4096)
    if not data:
        continue
    ts = time.strftime("%H:%M:%S")
    print(f"{ts}  IN  {len(data):3} B  {data.hex(' ')}", flush=True)
    time.sleep(0.02)
    os.write(fd, REPLY)
    print(f"{ts}  OUT {len(REPLY):3} B  {REPLY.hex(' ')}  <- canned POLL reply", flush=True)