"""AsyncEngine — the serving runtime (design_v3 §6; plan M3).

A real request queue, lifecycle state machine, live streaming, and step-level concurrency over the
same step scheduler. Each request runs as an asyncio task that ticks its runner one step at a time
and yields the event loop (`await asyncio.sleep(0)`), so concurrent requests interleave at step
granularity — and a per-request stall backs off instead of busy-spinning. Drives BOTH inline
``ProgramRunner`` and ``DisaggregatedRunner`` (capacity-aware pool dispatch) through one driver.

Cancellation is common-path (design_v3 §6.4): ``cancel(request_id)`` trips the runner's CancelScope,
which raises at the next step boundary and delivers partial artifacts + a structured ``cancelled``.
"""
from __future__ import annotations

import asyncio
from typing import Any, AsyncIterator

from v2.request.artifacts import Output
from v2.request.cancel import Cancelled
from v2.request.streams import OmniEvent
from v2.runtime.disaggregated import DisaggregatedRunner
from v2.runtime.engine import Engine

_SENTINEL = object()


def _safe_put(q: "asyncio.Queue", item: Any) -> None:
    """Non-blocking put on an unbounded queue — safe to call from finally/cancellation paths."""
    try:
        q.put_nowait(item)
    except Exception:
        pass


class RequestState:
    WAITING = "waiting"
    RUNNING = "running"
    COMPLETED = "completed"
    CANCELLED = "cancelled"
    FAILED = "failed"


class AsyncEngine:
    def __init__(self, engine: Engine | None = None, *, max_stall_ticks: int = 200_000,
                 max_history: int = 512):
        self.engine = engine if engine is not None else Engine()
        self._disagg: dict[str, tuple] = {}                 # model_id -> (PoolSet, Program)
        self._events: dict[str, asyncio.Queue] = {}
        self._states: dict[str, str] = {}
        self._results: dict[str, Output] = {}
        self._runners: dict[str, Any] = {}
        self._order: list[str] = []                         # submission order, for bounded eviction
        self.max_stall_ticks = max_stall_ticks
        self.max_history = max_history

    def _evict(self) -> None:
        """Bound retained per-request state to the most recent ``max_history`` terminal requests."""
        terminal = (RequestState.COMPLETED, RequestState.CANCELLED, RequestState.FAILED)
        i = 0
        while len(self._order) > self.max_history and i < len(self._order):
            rid = self._order[i]
            if self._states.get(rid) in terminal:
                self._order.pop(i)
                self._events.pop(rid, None)
                self._states.pop(rid, None)
                self._results.pop(rid, None)
                self._runners.pop(rid, None)
            else:
                i += 1

    # --- registration ------------------------------------------------------- #
    def register(self, model_id: str, instance: Any, program: Any) -> None:
        self.engine.register(model_id, instance, program)

    def register_disaggregated(self, model_id: str, pools: Any, program: Any) -> None:
        self._disagg[model_id] = (pools, program)

    def register_workflow(self, workflow: Any) -> Any:
        return self.engine.register_workflow(workflow)

    def is_disaggregated(self, model_id: str) -> bool:
        return model_id in self._disagg

    def _make_runner(self, request: Any) -> Any:
        if request.model_id in self._disagg:
            pools, program = self._disagg[request.model_id]
            return DisaggregatedRunner(pools, program, request,
                                       observers=self.engine.observers, interceptors=self.engine.interceptors)
        return self.engine._make_runner(request)

    # --- lifecycle / control ------------------------------------------------ #
    def state(self, request_id: str) -> str | None:
        return self._states.get(request_id)

    def cancel(self, request_id: str) -> bool:
        runner = self._runners.get(request_id)
        if runner is not None and getattr(runner, "cancel_scope", None) is not None:
            runner.cancel_scope.cancel()
            return True
        return False

    def result(self, request_id: str) -> Output | None:
        return self._results.get(request_id)

    @property
    def in_flight(self) -> int:
        return sum(1 for s in self._states.values() if s == RequestState.RUNNING)

    @property
    def queue_depth(self) -> int:
        return sum(1 for s in self._states.values() if s == RequestState.WAITING)

    def serves(self, model_id: str) -> bool:
        return (model_id in self.engine._registry or model_id in self._disagg
                or model_id in self.engine._workflows)

    # --- the driver: one asyncio task per request --------------------------- #
    async def _run(self, request: Any) -> None:
        rid = request.request_id
        evq = self._events[rid]
        runner = None
        stream_cursor = 0
        stall = 0
        try:
            runner = self._make_runner(request)
            self._runners[rid] = runner
            self._states[rid] = RequestState.RUNNING
            await evq.put(OmniEvent("request.start", rid, payload={"task": request.task.value}))
            while not runner.done:
                runner.cancel_scope.check()                  # common-path cancellation (step boundary)
                p0 = runner._progress
                runner.tick()
                # surface any newly emitted media chunks as live events
                events = runner.stream.events
                while stream_cursor < len(events):
                    await evq.put(events[stream_cursor])
                    stream_cursor += 1
                if not runner.done and runner._progress == p0:
                    stall += 1
                    if stall > self.max_stall_ticks:
                        raise RuntimeError(f"request {rid} stalled (state={getattr(runner,'state','?')})")
                    await asyncio.sleep(0.0005)              # backpressure backoff (capacity wait)
                else:
                    stall = 0
                    await asyncio.sleep(0)                   # cooperative yield → step interleaving
            out = runner.output()
            self._results[rid] = out
            for name in out.artifacts:
                await evq.put(OmniEvent("artifact.ready", rid, payload={"name": name}))
            self._states[rid] = RequestState.COMPLETED
            await evq.put(OmniEvent("request.complete", rid, payload={"metrics": dict(out.metrics)}))
        except Cancelled:
            self._states[rid] = RequestState.CANCELLED
            if runner is not None and hasattr(runner, "output"):
                try:
                    partial = runner.output()
                    partial.error = "cancelled"
                    self._results[rid] = partial
                except Exception:
                    pass
            _safe_put(evq, OmniEvent("request.cancelled", rid))
        except asyncio.CancelledError:                       # driver task cancelled (e.g. client gone)
            self._states[rid] = RequestState.CANCELLED
            raise
        except Exception as e:  # noqa: BLE001 — request-fatal isolation: one request's error
            self._states[rid] = RequestState.FAILED
            self._results[rid] = Output(request_id=rid, error=str(e))
            _safe_put(evq, OmniEvent("request.failed", rid, payload={"error": str(e)}))
        finally:
            # release any pool this request occupied — a cancel/error mid-loop must NOT leak capacity
            if runner is not None and hasattr(runner, "close"):
                try:
                    runner.close()
                except Exception:
                    pass
            _safe_put(evq, _SENTINEL)
            self._evict()

    async def submit(self, request: Any) -> AsyncIterator[OmniEvent]:
        """Submit a request and stream its events live (request.start → media.chunk* → artifact.ready*
        → request.complete | request.cancelled | request.failed). Cancels the driver if the consumer
        abandons the stream (e.g. client disconnect), so no orphaned compute keeps running."""
        rid = request.request_id
        if rid in self._events and self._states.get(rid) in (RequestState.WAITING, RequestState.RUNNING):
            raise ValueError(f"request_id {rid!r} is already in flight")
        self._events[rid] = asyncio.Queue()
        self._states[rid] = RequestState.WAITING
        self._order.append(rid)
        task = asyncio.create_task(self._run(request))
        evq = self._events[rid]
        try:
            while True:
                ev = await evq.get()
                if ev is _SENTINEL:
                    break
                yield ev
        finally:
            if not task.done():
                task.cancel()
            try:
                await task
            except (asyncio.CancelledError, Exception):     # noqa: BLE001
                pass

    async def generate(self, request: Any) -> Output:
        """Non-streaming: drive to completion, return the Output (the offline path over the queue)."""
        async for _ in self.submit(request):
            pass
        return self._results[request.request_id]

    async def generate_many(self, requests: list[Any]) -> dict[str, Output]:
        """Run requests concurrently (they interleave at step granularity through the event loop)."""
        await asyncio.gather(*(self._drain(r) for r in requests))
        return {r.request_id: self._results[r.request_id] for r in requests}

    async def _drain(self, request: Any) -> None:
        async for _ in self.submit(request):
            pass