"""In-memory stream bridge backed by :class:`asyncio.Queue`."""

from __future__ import annotations

import asyncio
import logging
import time
from collections.abc import AsyncIterator
from typing import Any

from .base import END_SENTINEL, HEARTBEAT_SENTINEL, StreamBridge, StreamEvent

logger = logging.getLogger(__name__)

_PUBLISH_TIMEOUT = 30.0  # seconds to wait when queue is full


class MemoryStreamBridge(StreamBridge):
    """Per-run ``asyncio.Queue`` implementation.

    Each *run_id* gets its own queue on first :meth:`publish` call.
    """

    def __init__(self, *, queue_maxsize: int = 256) -> None:
        self._maxsize = queue_maxsize
        self._queues: dict[str, asyncio.Queue[StreamEvent]] = {}
        self._counters: dict[str, int] = {}
        self._dropped_counts: dict[str, int] = {}

    # -- helpers ---------------------------------------------------------------

    def _get_or_create_queue(self, run_id: str) -> asyncio.Queue[StreamEvent]:
        if run_id not in self._queues:
            self._queues[run_id] = asyncio.Queue(maxsize=self._maxsize)
            self._counters[run_id] = 0
            self._dropped_counts[run_id] = 0
        return self._queues[run_id]

    def _next_id(self, run_id: str) -> str:
        self._counters[run_id] = self._counters.get(run_id, 0) + 1
        ts = int(time.time() * 1000)
        seq = self._counters[run_id] - 1
        return f"{ts}-{seq}"

    # -- StreamBridge API ------------------------------------------------------

    async def publish(self, run_id: str, event: str, data: Any) -> None:
        queue = self._get_or_create_queue(run_id)
        entry = StreamEvent(id=self._next_id(run_id), event=event, data=data)
        try:
            await asyncio.wait_for(queue.put(entry), timeout=_PUBLISH_TIMEOUT)
        except TimeoutError:
            self._dropped_counts[run_id] = self._dropped_counts.get(run_id, 0) + 1
            logger.warning(
                "Stream bridge queue full for run %s — dropping event %s (total dropped: %d)",
                run_id,
                event,
                self._dropped_counts[run_id],
            )

    async def publish_end(self, run_id: str) -> None:
        queue = self._get_or_create_queue(run_id)

        # END sentinel is critical — it is the only signal that allows
        # subscribers to terminate.  If the queue is full we evict the
        # oldest *regular* events to make room rather than dropping END,
        # which would cause the SSE connection to hang forever and leak
        # the queue/counter resources for this run_id.
        if queue.full():
            evicted = 0
            while queue.full():
                try:
                    queue.get_nowait()
                    evicted += 1
                except asyncio.QueueEmpty:
                    break  # pragma: no cover – defensive
            if evicted:
                logger.warning(
                    "Stream bridge queue full for run %s — evicted %d event(s) to guarantee END sentinel delivery",
                    run_id,
                    evicted,
                )

        # After eviction the queue is guaranteed to have space, so a
        # simple non-blocking put is safe.  We still use put() (which
        # blocks until space is available) as a defensive measure.
        await queue.put(END_SENTINEL)

    async def subscribe(
        self,
        run_id: str,
        *,
        last_event_id: str | None = None,
        heartbeat_interval: float = 15.0,
    ) -> AsyncIterator[StreamEvent]:
        if last_event_id is not None:
            logger.debug("last_event_id=%s accepted but ignored (memory bridge has no replay)", last_event_id)

        queue = self._get_or_create_queue(run_id)
        while True:
            try:
                entry = await asyncio.wait_for(queue.get(), timeout=heartbeat_interval)
            except TimeoutError:
                yield HEARTBEAT_SENTINEL
                continue
            if entry is END_SENTINEL:
                yield END_SENTINEL
                return
            yield entry

    async def cleanup(self, run_id: str, *, delay: float = 0) -> None:
        if delay > 0:
            await asyncio.sleep(delay)
        self._queues.pop(run_id, None)
        self._counters.pop(run_id, None)
        self._dropped_counts.pop(run_id, None)

    async def close(self) -> None:
        self._queues.clear()
        self._counters.clear()
        self._dropped_counts.clear()

    def dropped_count(self, run_id: str) -> int:
        """Return the number of events dropped for *run_id*."""
        return self._dropped_counts.get(run_id, 0)

    @property
    def dropped_total(self) -> int:
        """Return the total number of events dropped across all runs."""
        return sum(self._dropped_counts.values())