terra-view/backend/routers/slmm.py

"""
SLMM (Sound Level Meter Manager) Proxy Router

Proxies requests from SFM to the standalone SLMM backend service.
SLMM runs on port 8100 and handles NL43/NL53 sound level meter communication.
"""

from fastapi import APIRouter, HTTPException, Request, Response, WebSocket, WebSocketDisconnect
from fastapi.responses import StreamingResponse
import httpx
import websockets
import asyncio
import logging
import os

logger = logging.getLogger(__name__)

router = APIRouter(prefix="/api/slmm", tags=["slmm"])

# SLMM backend URL - configurable via environment variable
SLMM_BASE_URL = os.getenv("SLMM_BASE_URL", "http://localhost:8100")
# WebSocket URL derived from HTTP URL
SLMM_WS_BASE_URL = SLMM_BASE_URL.replace("http://", "ws://").replace("https://", "wss://")


@router.get("/health")
async def check_slmm_health():
    """
    Check if the SLMM backend service is reachable and healthy.
    """
    try:
        async with httpx.AsyncClient(timeout=5.0) as client:
            response = await client.get(f"{SLMM_BASE_URL}/health")

            if response.status_code == 200:
                data = response.json()
                return {
                    "status": "ok",
                    "slmm_status": "connected",
                    "slmm_url": SLMM_BASE_URL,
                    "slmm_version": data.get("version", "unknown"),
                    "slmm_response": data
                }
            else:
                return {
                    "status": "degraded",
                    "slmm_status": "error",
                    "slmm_url": SLMM_BASE_URL,
                    "detail": f"SLMM returned status {response.status_code}"
                }

    except httpx.ConnectError:
        return {
            "status": "error",
            "slmm_status": "unreachable",
            "slmm_url": SLMM_BASE_URL,
            "detail": "Cannot connect to SLMM backend. Is it running?"
        }
    except Exception as e:
        return {
            "status": "error",
            "slmm_status": "error",
            "slmm_url": SLMM_BASE_URL,
            "detail": str(e)
        }


# WebSocket routes MUST come before the catch-all route
@router.websocket("/{unit_id}/stream")
async def proxy_websocket_stream(websocket: WebSocket, unit_id: str):
    """
    Proxy WebSocket connections to SLMM's /stream endpoint.

    This allows real-time streaming of measurement data from NL43 devices
    through the SFM unified interface.
    """
    await websocket.accept()
    logger.info(f"WebSocket connection accepted for SLMM unit {unit_id}")

    # Build target WebSocket URL
    target_ws_url = f"{SLMM_WS_BASE_URL}/api/nl43/{unit_id}/stream"
    logger.info(f"Connecting to SLMM WebSocket: {target_ws_url}")

    backend_ws = None

    try:
        # Connect to SLMM backend WebSocket
        backend_ws = await websockets.connect(target_ws_url)
        logger.info(f"Connected to SLMM backend WebSocket for {unit_id}")

        # Create tasks for bidirectional communication
        async def forward_to_backend():
            """Forward messages from client to SLMM backend"""
            try:
                while True:
                    data = await websocket.receive_text()
                    await backend_ws.send(data)
            except WebSocketDisconnect:
                logger.info(f"Client WebSocket disconnected for {unit_id}")
            except Exception as e:
                logger.error(f"Error forwarding to backend: {e}")

        async def forward_to_client():
            """Forward messages from SLMM backend to client"""
            try:
                async for message in backend_ws:
                    await websocket.send_text(message)
            except websockets.exceptions.ConnectionClosed:
                logger.info(f"Backend WebSocket closed for {unit_id}")
            except Exception as e:
                logger.error(f"Error forwarding to client: {e}")

        # Run both forwarding tasks concurrently
        await asyncio.gather(
            forward_to_backend(),
            forward_to_client(),
            return_exceptions=True
        )

    except websockets.exceptions.WebSocketException as e:
        logger.error(f"WebSocket error connecting to SLMM backend: {e}")
        try:
            await websocket.send_json({
                "error": "Failed to connect to SLMM backend",
                "detail": str(e)
            })
        except Exception:
            pass
    except Exception as e:
        logger.error(f"Unexpected error in WebSocket proxy for {unit_id}: {e}")
        try:
            await websocket.send_json({
                "error": "Internal server error",
                "detail": str(e)
            })
        except Exception:
            pass
    finally:
        # Clean up connections
        if backend_ws:
            try:
                await backend_ws.close()
            except Exception:
                pass
        try:
            await websocket.close()
        except Exception:
            pass
        logger.info(f"WebSocket proxy closed for {unit_id}")


@router.websocket("/{unit_id}/live")
async def proxy_websocket_live(websocket: WebSocket, unit_id: str):
    """
    Proxy WebSocket connections to SLMM's /live endpoint.

    Alternative WebSocket endpoint that may be used by some frontend components.
    """
    await websocket.accept()
    logger.info(f"WebSocket connection accepted for SLMM unit {unit_id} (live endpoint)")

    # Build target WebSocket URL - try /stream endpoint as SLMM uses that for WebSocket
    target_ws_url = f"{SLMM_WS_BASE_URL}/api/nl43/{unit_id}/stream"
    logger.info(f"Connecting to SLMM WebSocket: {target_ws_url}")

    backend_ws = None

    try:
        # Connect to SLMM backend WebSocket
        backend_ws = await websockets.connect(target_ws_url)
        logger.info(f"Connected to SLMM backend WebSocket for {unit_id} (live endpoint)")

        # Create tasks for bidirectional communication
        async def forward_to_backend():
            """Forward messages from client to SLMM backend"""
            try:
                while True:
                    data = await websocket.receive_text()
                    await backend_ws.send(data)
            except WebSocketDisconnect:
                logger.info(f"Client WebSocket disconnected for {unit_id} (live)")
            except Exception as e:
                logger.error(f"Error forwarding to backend (live): {e}")

        async def forward_to_client():
            """Forward messages from SLMM backend to client"""
            try:
                async for message in backend_ws:
                    await websocket.send_text(message)
            except websockets.exceptions.ConnectionClosed:
                logger.info(f"Backend WebSocket closed for {unit_id} (live)")
            except Exception as e:
                logger.error(f"Error forwarding to client (live): {e}")

        # Run both forwarding tasks concurrently
        await asyncio.gather(
            forward_to_backend(),
            forward_to_client(),
            return_exceptions=True
        )

    except websockets.exceptions.WebSocketException as e:
        logger.error(f"WebSocket error connecting to SLMM backend (live): {e}")
        try:
            await websocket.send_json({
                "error": "Failed to connect to SLMM backend",
                "detail": str(e)
            })
        except Exception:
            pass
    except Exception as e:
        logger.error(f"Unexpected error in WebSocket proxy for {unit_id} (live): {e}")
        try:
            await websocket.send_json({
                "error": "Internal server error",
                "detail": str(e)
            })
        except Exception:
            pass
    finally:
        # Clean up connections
        if backend_ws:
            try:
                await backend_ws.close()
            except Exception:
                pass
        try:
            await websocket.close()
        except Exception:
            pass
        logger.info(f"WebSocket proxy closed for {unit_id} (live)")


@router.websocket("/{unit_id}/monitor")
async def proxy_websocket_monitor(websocket: WebSocket, unit_id: str):
    """
    Proxy WebSocket connections to SLMM's /monitor (fan-out DOD feed).

    This is the shared ~1Hz DOD feed: many clients subscribe to one device feed
    (no single-connection contention) and it carries L1/L10 (which the DRD
    /stream cannot). Preferred over /stream for the live view.
    """
    await websocket.accept()
    logger.info(f"WebSocket accepted for SLMM unit {unit_id} (monitor)")

    target_ws_url = f"{SLMM_WS_BASE_URL}/api/nl43/{unit_id}/monitor"
    backend_ws = None

    try:
        backend_ws = await websockets.connect(target_ws_url)
        logger.info(f"Connected to SLMM monitor feed for {unit_id}")

        async def forward_to_client():
            """Backend monitor frames -> browser."""
            async for message in backend_ws:
                await websocket.send_text(message)

        async def watch_client():
            """Drain client frames; raises WebSocketDisconnect on close so we can
            tear the pair down (the monitor feed is server->client only)."""
            while True:
                await websocket.receive_text()

        # When EITHER side ends (browser disconnects or backend closes), cancel the
        # other immediately — avoids sending into a closed socket (the
        # "Unexpected ASGI message after close" race that asyncio.gather leaves open).
        tasks = [asyncio.ensure_future(forward_to_client()),
                 asyncio.ensure_future(watch_client())]
        done, pending = await asyncio.wait(tasks, return_when=asyncio.FIRST_COMPLETED)
        for t in pending:
            t.cancel()
        for t in pending:
            try:
                await t
            except Exception:
                pass

    except websockets.exceptions.WebSocketException as e:
        logger.error(f"WebSocket error connecting to SLMM monitor for {unit_id}: {e}")
        try:
            await websocket.send_json({"error": "Failed to connect to SLMM monitor", "detail": str(e)})
        except Exception:
            pass
    except Exception as e:
        logger.error(f"Unexpected error in monitor proxy for {unit_id}: {e}")
    finally:
        if backend_ws:
            try:
                await backend_ws.close()
            except Exception:
                pass
        try:
            await websocket.close()
        except Exception:
            pass
        logger.info(f"WebSocket monitor proxy closed for {unit_id}")


# HTTP catch-all route MUST come after specific routes (including WebSocket routes)
@router.api_route("/{path:path}", methods=["GET", "POST", "PUT", "DELETE", "PATCH"])
async def proxy_to_slmm(path: str, request: Request):
    """
    Proxy all requests to the SLMM backend service.

    This allows SFM to act as a unified frontend for all device types,
    while SLMM remains a standalone backend service.
    """
    # Build target URL
    target_url = f"{SLMM_BASE_URL}/api/nl43/{path}"

    # Get query parameters
    query_params = dict(request.query_params)

    # Get request body if present
    body = None
    if request.method in ["POST", "PUT", "PATCH"]:
        try:
            body = await request.body()
        except Exception as e:
            logger.error(f"Failed to read request body: {e}")
            body = None

    # Get headers (exclude host and other proxy-specific headers)
    headers = dict(request.headers)
    headers_to_exclude = ["host", "content-length", "transfer-encoding", "connection"]
    proxy_headers = {k: v for k, v in headers.items() if k.lower() not in headers_to_exclude}

    logger.info(f"Proxying {request.method} request to SLMM: {target_url}")

    try:
        async with httpx.AsyncClient(timeout=30.0) as client:
            # Forward the request to SLMM
            response = await client.request(
                method=request.method,
                url=target_url,
                params=query_params,
                headers=proxy_headers,
                content=body
            )

            # Return the response from SLMM
            return Response(
                content=response.content,
                status_code=response.status_code,
                headers=dict(response.headers),
                media_type=response.headers.get("content-type")
            )

    except httpx.ConnectError:
        logger.error(f"Failed to connect to SLMM backend at {SLMM_BASE_URL}")
        raise HTTPException(
            status_code=503,
            detail=f"SLMM backend service unavailable. Is SLMM running on {SLMM_BASE_URL}?"
        )
    except httpx.TimeoutException:
        logger.error(f"Timeout connecting to SLMM backend at {SLMM_BASE_URL}")
        raise HTTPException(
            status_code=504,
            detail="SLMM backend timeout"
        )
    except Exception as e:
        logger.error(f"Error proxying to SLMM: {e}")
        raise HTTPException(
            status_code=500,
            detail=f"Failed to proxy request to SLMM: {str(e)}"
        )