#!/usr/bin/env python3
"""
RION NL-42 / NL-52 USB serial probe — zero dependencies (stdlib termios only).

The NL-52's USB port enumerates as a virtual COM port ("RION USB to RS232C
Converter"). On Linux that is almost always handled by an in-kernel USB-serial
driver (ftdi_sio / cp210x / ch341) which creates /dev/ttyUSB*. This script
opens that port and sends a few harmless REQUEST commands (no settings are
changed) to confirm two-way communication.

Protocol (NL-42/NL-52 Serial Interface Manual 55779):
  Request:  "<Command>?"          + CRLF
  Setting:  "$<Command>,<param>"  + CRLF      (NOT used here — read-only probe)
  Reply:    result code "R+0000"  + CRLF, then data line(s) for requests.

Before running:
  1. On the meter: MENU -> I/O -> Communication Interface -> "USB"
     (set this BEFORE plugging in the cable).
  2. Connect a generic USB-A -> mini-B cable directly (no hub).
  3. Find the port:  ls -l /dev/ttyUSB*   (and `dmesg | tail` after plugging in)

Usage:
  python3 nl52_usb_probe.py                      # defaults to /dev/ttyUSB0
  python3 nl52_usb_probe.py --port /dev/ttyUSB0 --baud 115200
  python3 nl52_usb_probe.py --cmd "System Version?" --cmd "Clock?"
"""

import argparse
import os
import select
import sys
import termios
import time

# Safe, read-only probe commands (all are pure requests).
DEFAULT_COMMANDS = [
    "System Version?",   # firmware version — proves the link end-to-end
    "Clock?",            # current date/time
    "SD Card Free Size?",
    "DOD?",              # snapshot of currently displayed values
]

BAUD_CONSTANTS = {
    9600: termios.B9600,
    19200: termios.B19200,
    38400: termios.B38400,
    57600: termios.B57600,
    115200: termios.B115200,
}


def open_serial(port: str, baud: int) -> int:
    """Open a serial port in raw 8N1, no flow control. Returns an fd."""
    if baud not in BAUD_CONSTANTS:
        raise ValueError(f"Unsupported baud {baud}; choose from {sorted(BAUD_CONSTANTS)}")

    fd = os.open(port, os.O_RDWR | os.O_NOCTTY | os.O_NONBLOCK)

    attrs = termios.tcgetattr(fd)
    iflag, oflag, cflag, lflag, ispeed, ospeed, cc = attrs

    # Raw mode
    iflag = 0
    oflag = 0
    lflag = 0
    # 8 data bits, enable receiver, ignore modem control lines
    cflag = termios.CS8 | termios.CREAD | termios.CLOCAL
    # (no PARENB = no parity, no CSTOPB = 1 stop bit, no CRTSCTS = no flow control)

    bconst = BAUD_CONSTANTS[baud]
    ispeed = bconst
    ospeed = bconst

    termios.tcsetattr(fd, termios.TCSANOW, [iflag, oflag, cflag, lflag, ispeed, ospeed, cc])
    termios.tcflush(fd, termios.TCIOFLUSH)
    return fd


def send(fd: int, line: str):
    os.write(fd, (line + "\r\n").encode("ascii"))


def read_reply(fd: int, timeout: float = 3.0) -> bytes:
    """Read whatever arrives within `timeout` seconds (idle-gap terminated)."""
    buf = bytearray()
    deadline = time.time() + timeout
    while time.time() < deadline:
        r, _, _ = select.select([fd], [], [], 0.3)
        if r:
            try:
                chunk = os.read(fd, 4096)
            except BlockingIOError:
                continue
            if chunk:
                buf.extend(chunk)
                # Once we've seen a CRLF and there's a brief idle, stop early
                deadline = min(deadline, time.time() + 0.4)
    return bytes(buf)


def main():
    ap = argparse.ArgumentParser(description="RION NL-42/NL-52 USB serial probe")
    ap.add_argument("--port", default="/dev/ttyUSB0")
    ap.add_argument("--baud", type=int, default=115200,
                    help="USB CDC usually ignores baud, but RS-232C needs a match")
    ap.add_argument("--cmd", action="append", dest="cmds",
                    help="Override probe command(s); repeatable")
    ap.add_argument("--timeout", type=float, default=3.0)
    args = ap.parse_args()

    commands = args.cmds or DEFAULT_COMMANDS

    if not os.path.exists(args.port):
        print(f"[!] {args.port} does not exist.")
        print("    Plug in the meter (Comm Interface = USB) and check: ls -l /dev/ttyUSB*")
        print("    Also check the kernel saw it:  dmesg | tail -20")
        return 2

    try:
        fd = open_serial(args.port, args.baud)
    except PermissionError:
        print(f"[!] Permission denied on {args.port}.")
        print("    Add yourself to the 'dialout' group, or run with sudo:")
        print(f"      sudo usermod -aG dialout $USER   (then log out/in)")
        return 2
    except Exception as e:
        print(f"[!] Could not open {args.port}: {e}")
        return 2

    print(f"[*] Opened {args.port} @ {args.baud} 8N1 (raw, no flow control)")
    print(f"[*] Sending {len(commands)} read-only request command(s)\n")

    ok = 0
    try:
        for cmd in commands:
            send(fd, cmd)
            reply = read_reply(fd, args.timeout)
            decoded = reply.decode("ascii", errors="replace").replace("\r", "\\r").replace("\n", "\\n\n")
            if reply:
                ok += 1
                print(f"  > {cmd}")
                for line in decoded.splitlines():
                    print(f"      {line}")
            else:
                print(f"  > {cmd}")
                print(f"      (no response within {args.timeout}s)")
            print()
            time.sleep(1.0)  # NL-series likes >=1s between commands
    finally:
        os.close(fd)

    if ok == 0:
        print("[!] No responses. Things to check:")
        print("    - Meter's Communication Interface is set to USB (not RS-232C)")
        print("    - ECO / Sleep mode is OFF (both disable the comm interface)")
        print("    - Right port (try other /dev/ttyUSB* or /dev/ttyACM*)")
        print("    - For RS-232C path, baud must match the meter's setting")
        return 1

    print(f"[OK] {ok}/{len(commands)} commands answered — two-way comms confirmed.")
    return 0


if __name__ == "__main__":
    sys.exit(main())