import asyncio
import json
import time
import serial
from fastapi import FastAPI, WebSocket, WebSocketDisconnect
from fastapi.responses import HTMLResponse

SERIAL_PORT = "/dev/ttyACM0"   # ggf. /dev/ttyUSB0
BAUD = 115200

# Safety: if websocket stops sending, we also stop.
STOP_AFTER_SEC = 0.35

app = FastAPI()

ser = serial.Serial(SERIAL_PORT, BAUD, timeout=0)

last_msg_ts = 0.0

def clamp255(v: int) -> int:
  return max(-255, min(255, int(v)))

def send_lr(l: int, r: int):
  l = clamp255(l)
  r = clamp255(r)
  line = f"L {l} R {r}\n".encode("ascii")
  ser.write(line)

@app.get("/health")
def health():
  return {"ok": True, "serial": SERIAL_PORT}

@app.websocket("/ws")
async def ws(websocket: WebSocket):
  global last_msg_ts
  await websocket.accept()

  async def watchdog():
    while True:
      await asyncio.sleep(0.05)
      if time.time() - last_msg_ts > STOP_AFTER_SEC:
        send_lr(0, 0)

  wd_task = asyncio.create_task(watchdog())

  try:
    while True:
      msg = await websocket.receive_text()
      last_msg_ts = time.time()

      try:
        data = json.loads(msg)
        l = clamp255(data.get("l", 0))
        r = clamp255(data.get("r", 0))
        send_lr(l, r)
      except Exception:
        # On parse errors: stop
        send_lr(0, 0)

      await websocket.send_text("ok")
  except WebSocketDisconnect:
    send_lr(0, 0)
  finally:
    wd_task.cancel()