"""SSE endpoint per live progress del training.

GET /api/trainings/{id}/events
  Streamma eventi dal Redis stream `ml:train:{id}:events` via Server-Sent Events.
  Termina quando lo stato del training è terminale (succeeded/failed/cancelled).
"""
from __future__ import annotations

import asyncio
import json
import uuid

from fastapi import APIRouter, Depends, HTTPException
from sse_starlette.sse import EventSourceResponse

from core import db, redis_client
from core.auth import require_auth

router = APIRouter(prefix="/api/trainings", tags=["trainings-sse"])

_TERMINAL = {"succeeded", "failed", "cancelled"}


@router.get("/{training_id}/events")
async def training_events(training_id: str, user=Depends(require_auth)):
    # verifica esistenza
    row = await db.fetchrow("SELECT status FROM trainings WHERE id = $1", uuid.UUID(training_id))
    if not row:
        raise HTTPException(404, "not found")

    stream_key = f"ml:train:{training_id}:events"
    status_key = f"ml:train:{training_id}"

    async def gen():
        last_id = "0-0"
        r = redis_client.client()
        while True:
            try:
                # XREAD block 5s per non tenere la connessione idle troppo a lungo
                resp = await r.xread({stream_key: last_id}, count=50, block=5000)
            except Exception as e:
                yield {"event": "error", "data": json.dumps({"error": str(e)})}
                await asyncio.sleep(1)
                continue

            if resp:
                for _stream, entries in resp:
                    for entry_id, fields in entries:
                        last_id = entry_id
                        yield {"event": "message", "id": entry_id, "data": json.dumps(fields)}

            # controlla stato terminale
            state = await r.hget(status_key, "status")
            if not state:
                # fallback su db se redis scaduto
                db_row = await db.fetchrow(
                    "SELECT status FROM trainings WHERE id = $1", uuid.UUID(training_id)
                )
                state = db_row["status"] if db_row else "unknown"
            if state in _TERMINAL:
                yield {"event": "end", "data": json.dumps({"status": state})}
                return

    return EventSourceResponse(gen())