"""回忆录后台任务聚合：debounce 后派发 process_memoir_phase1；flush 时触发待叙事 Phase2。"""

from __future__ import annotations

import asyncio
import time
from dataclasses import dataclass, field
from typing import Dict, List, Sequence

from app.core.config import settings
from app.core.logging import get_logger
from app.core.task_tracker import task_tracker

logger = get_logger(__name__)


def _batch_ready_for_submit(
    *,
    min_chars: int,
    max_wait_seconds: float,
    total_text_chars: int,
    elapsed_seconds: float,
) -> bool:
    """字数门闸开启时，静默结束后是否应提交（不含 min_chars==0 的早退，由调用方处理）。"""
    if min_chars <= 0:
        return True
    if total_text_chars >= min_chars:
        return True
    if max_wait_seconds <= 0:
        return True
    return elapsed_seconds >= max_wait_seconds


def _next_retry_sleep_seconds(
    debounce_seconds: float,
    max_wait_seconds: float,
    elapsed_seconds: float,
) -> float:
    """未达字数且未超时：下次再 sleep 的秒数。"""
    return min(debounce_seconds, max(0.0, max_wait_seconds - elapsed_seconds))


@dataclass
class _MemoirBatchState:
    segment_ids: list[str] = field(default_factory=list)
    total_text_chars: int = 0
    first_queued_monotonic: float | None = None


class BackgroundTaskRunner:
    def __init__(self, debounce_seconds: int = 5) -> None:
        self.debounce_seconds = debounce_seconds
        self._batch: Dict[str, _MemoirBatchState] = {}
        self._timers: Dict[str, asyncio.Task[None]] = {}

    def _pop_batch(self, user_id: str) -> list[str]:
        st = self._batch.pop(user_id, None)
        if not st or not st.segment_ids:
            return []
        ids = st.segment_ids
        return ids

    async def _flush_pending_phase2(self, user_id: str) -> None:
        try:
            from app.tasks.memoir_tasks import dispatch_pending_memoir_phase2_for_user

            await asyncio.to_thread(dispatch_pending_memoir_phase2_for_user, user_id)
        except Exception as e:
            logger.error(
                "flush Phase2 失败: user_id={} exc_type={} exc={}",
                user_id,
                type(e).__name__,
                e,
            )

    async def _submit_task(self, user_id: str, segment_ids: List[str]) -> str | None:
        try:
            from app.tasks.memoir_tasks import process_memoir_phase1

            result = process_memoir_phase1.delay(user_id, segment_ids)
            task_id = result.id
            await task_tracker.add_task(user_id, task_id, "memoir")
            logger.info(
                "已提交 Celery 任务: user_id={}, task_id={}, segments={}",
                user_id,
                task_id,
                len(segment_ids),
            )
            return task_id
        except Exception as e:
            logger.error("提交 Celery 任务失败: {}", e)
            return None

    async def queue_message(
        self, user_id: str, segment_id: str, *, text_char_count: int = 0
    ) -> None:
        st = self._batch.setdefault(user_id, _MemoirBatchState())
        if not st.segment_ids:
            st.first_queued_monotonic = time.monotonic()
        st.segment_ids.append(segment_id)
        st.total_text_chars += max(0, text_char_count)

        if user_id in self._timers:
            self._timers[user_id].cancel()

        async def delayed_submit() -> None:
            try:
                await asyncio.sleep(self.debounce_seconds)
                while True:
                    if user_id not in self._batch:
                        return
                    batch = self._batch.get(user_id)
                    if not batch or not batch.segment_ids:
                        return

                    min_c = int(settings.memoir_segment_batch_min_chars)
                    max_w = float(settings.memoir_segment_batch_max_wait_seconds)

                    if min_c <= 0:
                        segment_ids = self._pop_batch(user_id)
                        if segment_ids:
                            await self._submit_task(user_id, segment_ids)
                        return

                    first = batch.first_queued_monotonic
                    if first is None:
                        segment_ids = self._pop_batch(user_id)
                        if segment_ids:
                            await self._submit_task(user_id, segment_ids)
                        return

                    now = time.monotonic()
                    elapsed = now - first
                    total = batch.total_text_chars

                    if _batch_ready_for_submit(
                        min_chars=min_c,
                        max_wait_seconds=max_w,
                        total_text_chars=total,
                        elapsed_seconds=elapsed,
                    ):
                        segment_ids = self._pop_batch(user_id)
                        if segment_ids:
                            await self._submit_task(user_id, segment_ids)
                        return

                    sleep_more = _next_retry_sleep_seconds(
                        float(self.debounce_seconds),
                        max_w,
                        elapsed,
                    )
                    if sleep_more <= 0:
                        segment_ids = self._pop_batch(user_id)
                        if segment_ids:
                            await self._submit_task(user_id, segment_ids)
                        return
                    await asyncio.sleep(sleep_more)
            except asyncio.CancelledError:
                pass
            except Exception as e:
                logger.error("延迟提交任务失败: {}", e)

        self._timers[user_id] = asyncio.create_task(delayed_submit())

    def _dedupe_preserve_order(self, ids: Sequence[str]) -> list[str]:
        seen: set[str] = set()
        out: list[str] = []
        for sid in ids:
            if sid not in seen:
                seen.add(sid)
                out.append(sid)
        return out

    async def flush_pending(
        self,
        user_id: str,
        *,
        extra_segment_ids: Sequence[str] | None = None,
    ) -> str | None:
        if user_id in self._timers:
            self._timers[user_id].cancel()
            del self._timers[user_id]
        popped = self._pop_batch(user_id)
        merged = self._dedupe_preserve_order(
            list(popped) + list(extra_segment_ids or ())
        )
        task_id: str | None = None
        if merged:
            task_id = await self._submit_task(user_id, merged)
        await self._flush_pending_phase2(user_id)
        return task_id