"""POST /v1/lab/feedback — SSE stream of Lab in-flow feedback (REQ-2-007).

D-016 envelope with agent=lab. Unknown scenario → 404 before streaming.
"""

import json
from collections.abc import AsyncIterator

from fastapi import APIRouter, Depends, HTTPException
from pydantic import BaseModel, Field
from sse_starlette.sse import EventSourceResponse

from ..agents.registry import AgentRegistry
from ..config import Settings
from ..corpus.learner_context import get_learner_context
from ..corpus.telemetry import get_lab_scenario
from .deps import get_agent_registry, get_provider, get_settings

router = APIRouter(prefix="/v1")


class LabFeedbackRequest(BaseModel):
    scenario_id: str = Field(min_length=1)
    learner_id: str | None = None


@router.post("/lab/feedback")
async def lab_feedback(
    body: LabFeedbackRequest,
    registry: AgentRegistry = Depends(get_agent_registry),
    settings: Settings = Depends(get_settings),
    provider=Depends(get_provider),
) -> EventSourceResponse:
    scenario = get_lab_scenario(body.scenario_id)
    if scenario is None:
        raise HTTPException(
            status_code=404, detail=f"unknown scenario {body.scenario_id!r}"
        )
    agent = registry.get(provider, settings, "lab")
    learner_context = get_learner_context(body.learner_id)

    async def event_stream() -> AsyncIterator[dict]:
        yield {"event": "message", "data": json.dumps({
            "type": "meta",
            "agent": "lab",
            "scenario_id": body.scenario_id,
            "model": settings.model,
        })}
        first_byte = True
        try:
            async for token in agent.stream_feedback(scenario, learner_context):
                first_byte = False
                yield {"event": "message", "data": json.dumps({
                    "type": "delta", "content": token
                })}
            yield {"event": "message", "data": json.dumps({
                "type": "done", "finish_reason": "stop"
            })}
            yield {"event": "message", "data": "[DONE]"}
        except Exception as exc:
            code = "provider_unavailable" if first_byte else "provider_error"
            yield {"event": "message", "data": json.dumps({
                "type": "error", "code": code, "message": str(exc)
            })}
            # [DONE] from except, not finally — a yield in finally would
            # re-raise after GeneratorExit on client disconnect.
            yield {"event": "message", "data": "[DONE]"}

    return EventSourceResponse(
        event_stream(),
        headers={"Cache-Control": "no-cache", "X-Accel-Buffering": "no"},
    )