#!/usr/bin/env python3
"""Tiny TCP<->serial bridge for MUST PV1800 monitoring.

Listens on 127.0.0.1:$PROXY_PORT, forwards every byte to/from $PROXY_TTY
using pyserial. Multiple sequential TCP clients are served one at a time.
"""
import os, sys, threading, time
import serial, socket

PORT = int(os.environ.get("PROXY_PORT", "9700"))
TTY  = os.environ.get("PROXY_TTY", "/dev/ttyUSB0")
BAUD = int(os.environ.get("PROXY_BAUD", "19200"))

def log(msg):
    print(f"[must-proxy] {msg}", file=sys.stderr, flush=True)

try:
    # Pre-flush: read-and-discard whatever stale bytes are sitting in the
    # kernel TTY buffer from previous runs. Without this, those bytes get
    # delivered to the first client and corrupt its first read.
    pre = serial.Serial(TTY, BAUD, timeout=0.2)
    pre.reset_input_buffer()
    pre.reset_output_buffer()
    flushed = 0
    quiet_for = 0.0
    pre_start = time.monotonic()
    while time.monotonic() - pre_start < 3.0 and quiet_for < 0.3:
        chunk = pre.read(512)
        if chunk:
            flushed += len(chunk)
            quiet_for = 0.0
        else:
            quiet_for += 0.05
            time.sleep(0.05)
    pre.close()
    if flushed:
        log(f"flushed {flushed} stale bytes from kernel TTY buffer")

    ser = serial.Serial(TTY, BAUD, timeout=0.05)
    ser.reset_input_buffer()
    ser.reset_output_buffer()
    log(f"opened {TTY} @ {BAUD} fd={ser.fd}")
except Exception as e:
    log(f"could not open {TTY}: {e}")
    sys.exit(1)

def tty_to_tcp(client):
    while True:
        try:
            data = ser.read(256)
            if data:
                client.sendall(data)
        except Exception:
            return

srv = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
srv.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
srv.bind(("127.0.0.1", PORT))
srv.listen(5)
log(f"listening on 127.0.0.1:{PORT}")

while True:
    client, addr = srv.accept()
    log(f"client {addr}")
    threading.Thread(target=tty_to_tcp, args=(client,), daemon=True).start()
    try:
        while True:
            data = client.recv(4096)
            if not data:
                break
            ser.write(data)
            ser.flush()
    except Exception as e:
        log(f"tcp err: {e}")
    try:
        client.close()
    except Exception:
        pass
    log(f"client closed")