"""
SSE endpoint for chunker pipeline events.

Bridges gRPC StreamProgress to browser-native EventSource.
GET /api/chunker/stream/{job_id} → text/event-stream
"""

import asyncio
import json
import logging
import time
from typing import AsyncGenerator

from fastapi import APIRouter
from starlette.responses import StreamingResponse

logger = logging.getLogger(__name__)

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


async def _event_generator(job_id: str) -> AsyncGenerator[str, None]:
    """
    Generate SSE events by polling gRPC job state.

    Yields server-sent events in the format:
        event: <event_type>
        data: <json_payload>
    """
    from core.rpc.server import _active_jobs

    last_state = None
    timeout = time.monotonic() + 600  # 10 min max

    while time.monotonic() < timeout:
        job_state = _active_jobs.get(job_id)

        if job_state is None:
            # Job not found yet — may not have started
            yield f"event: waiting\ndata: {json.dumps({'job_id': job_id})}\n\n"
            await asyncio.sleep(0.5)
            continue

        # Only send if state changed
        if job_state != last_state:
            last_state = dict(job_state)
            event_type = job_state.get("status", "update")

            yield f"event: {event_type}\ndata: {json.dumps({**job_state, 'job_id': job_id})}\n\n"

            # End stream when job is terminal
            if event_type in ("completed", "failed", "cancelled"):
                yield f"event: done\ndata: {json.dumps({'job_id': job_id})}\n\n"
                break

        await asyncio.sleep(0.2)

    yield f"event: timeout\ndata: {json.dumps({'job_id': job_id})}\n\n"


@router.get("/stream/{job_id}")
async def stream_chunk_job(job_id: str):
    """
    SSE stream for a chunk pipeline job.

    The UI connects via native EventSource:
        const es = new EventSource('/api/chunker/stream/<job_id>');
        es.addEventListener('processing', (e) => { ... });
    """
    return StreamingResponse(
        _event_generator(job_id),
        media_type="text/event-stream",
        headers={
            "Cache-Control": "no-cache",
            "Connection": "keep-alive",
            "X-Accel-Buffering": "no",
        },
    )