"""
AWOOOI AIOps Phase 6 — Model Rollback 服務（決策衰退偵測）
==========================================================
職責：讀取最近 N 週的離線回放一致率，偵測連續衰退趨勢，
      在確認衰退後寫入 ai_governance_events（conservative_mode）
      並觸發 Telegram 告警通知 SRE 評估 retrain。

衰退定義：
  - 連續 4 週一致率下降（week[i] < week[i-1]）
  - 最新一週一致率 < 55%（絕對閾值）

設計原則：
  1. 不直接執行 retrain / model rollback — 只發通知 + 寫 governance event
  2. 自我降級連動：偵測到衰退 → conservative_mode event → decision_manager 讀取
  3. best-effort — 任何錯誤靜默記錄，不影響主流程
  4. feature flag: AIOPS_P6_GOVERNANCE_ENABLED

ADR-087 Phase 6: 自我治理閉環
2026-04-15 ogt + Claude Sonnet 4.6（亞太）: Phase 6 初始建立
"""

from __future__ import annotations

import uuid
from dataclasses import dataclass

import structlog
from sqlalchemy import and_, desc, select

from src.db.base import get_db_context
from src.db.models import AiGovernanceEvent
from src.utils.timezone import now_taipei

logger = structlog.get_logger(__name__)

# ─────────────────────────────────────────────────────────────────────────────
# 常數
# ─────────────────────────────────────────────────────────────────────────────

CONSECUTIVE_DECLINE_WEEKS = 4   # 連續衰退 N 週才觸發
ABSOLUTE_FLOOR_RATE = 0.55      # 一致率低於此值視為嚴重
RETRAIN_COOLDOWN_DAYS = 14      # 兩次 conservative_mode 事件間最短間隔


# ─────────────────────────────────────────────────────────────────────────────
# Result Types
# ─────────────────────────────────────────────────────────────────────────────

@dataclass
class RollbackCheckResult:
    """衰退偵測結果"""
    checked_weeks: int = 0
    consistency_rates: list[float] = None  # type: ignore[assignment]
    consecutive_declines: int = 0
    absolute_floor_breached: bool = False
    retrain_recommended: bool = False
    conservative_mode_triggered: bool = False
    cooldown_active: bool = False

    def __post_init__(self) -> None:
        if self.consistency_rates is None:
            self.consistency_rates = []


# ─────────────────────────────────────────────────────────────────────────────
# Service
# ─────────────────────────────────────────────────────────────────────────────

class ModelRollbackService:
    """
    Model Rollback 衰退偵測服務

    Usage:
        svc = ModelRollbackService()
        result = await svc.check()
    """

    async def check(self, force: bool = False) -> RollbackCheckResult:
        """
        檢查是否有決策衰退趨勢。

        Args:
            force: True 時繞過 feature flag
        """
        from src.core.feature_flags import aiops_flags
        if not force and not aiops_flags.AIOPS_P6_GOVERNANCE_ENABLED:
            logger.debug("model_rollback_check_skipped")
            return RollbackCheckResult()

        try:
            return await self._check()
        except Exception as e:
            logger.error("model_rollback_check_error", error=str(e))
            return RollbackCheckResult()

    async def _check(self) -> RollbackCheckResult:
        """讀取最近 N 次回放記錄，偵測衰退。"""
        async with get_db_context() as db:
            # 取最近 CONSECUTIVE_DECLINE_WEEKS + 1 筆回放記錄（包含 ok 和 degraded）
            stmt = (
                select(AiGovernanceEvent)
                .where(
                    AiGovernanceEvent.event_type.in_(["replay_ok", "replay_degraded"])
                )
                .order_by(desc(AiGovernanceEvent.triggered_at))
                .limit(CONSECUTIVE_DECLINE_WEEKS + 1)
            )
            result = await db.execute(stmt)
            events = list(result.scalars().all())

        if len(events) < 2:
            logger.info("model_rollback_insufficient_history", count=len(events))
            return RollbackCheckResult(checked_weeks=len(events))

        # 按時間由舊到新排列
        events.reverse()
        rates = []
        for ev in events:
            details = ev.details or {}
            rate = details.get("consistency_rate", 1.0)
            rates.append(float(rate))

        # 計算連續衰退次數（由新到舊）
        recent = rates[::-1]  # 最新在前
        consecutive = 0
        for i in range(len(recent) - 1):
            if recent[i] < recent[i + 1]:
                consecutive += 1
            else:
                break

        absolute_floor = rates[-1] < ABSOLUTE_FLOOR_RATE if rates else False
        retrain_recommended = (
            consecutive >= CONSECUTIVE_DECLINE_WEEKS or absolute_floor
        )

        result_obj = RollbackCheckResult(
            checked_weeks=len(rates),
            consistency_rates=rates,
            consecutive_declines=consecutive,
            absolute_floor_breached=absolute_floor,
            retrain_recommended=retrain_recommended,
        )

        if retrain_recommended:
            await self._maybe_trigger_conservative_mode(result_obj)

        logger.info(
            "model_rollback_check_done",
            consecutive_declines=consecutive,
            latest_rate=rates[-1] if rates else None,
            retrain_recommended=retrain_recommended,
        )
        return result_obj

    async def _maybe_trigger_conservative_mode(
        self, result: RollbackCheckResult
    ) -> None:
        """
        若距上次 conservative_mode 事件超過 RETRAIN_COOLDOWN_DAYS，
        寫入新的 conservative_mode 事件並發送告警。
        """
        from datetime import timedelta
        cutoff = now_taipei() - timedelta(days=RETRAIN_COOLDOWN_DAYS)

        async with get_db_context() as db:
            # 查是否在冷卻期內
            stmt = (
                select(AiGovernanceEvent)
                .where(
                    and_(
                        AiGovernanceEvent.event_type == "conservative_mode",
                        AiGovernanceEvent.triggered_at >= cutoff,
                    )
                )
                .limit(1)
            )
            recent_evt = (await db.execute(stmt)).scalar_one_or_none()

            if recent_evt:
                result.cooldown_active = True
                logger.info(
                    "model_rollback_conservative_mode_cooldown",
                    cooldown_days=RETRAIN_COOLDOWN_DAYS,
                )
                return

            # 寫入 conservative_mode 事件
            from sqlalchemy import insert as sa_insert
            await db.execute(
                sa_insert(AiGovernanceEvent).values(
                    id=str(uuid.uuid4()),
                    event_type="conservative_mode",
                    details={
                        "consecutive_declines": result.consecutive_declines,
                        "consistency_rates": result.consistency_rates,
                        "absolute_floor_breached": result.absolute_floor_breached,
                        "triggered_by": "model_rollback_service",
                    },
                    resolved=False,
                )
            )
            result.conservative_mode_triggered = True
            logger.warning(
                "model_rollback_conservative_mode_triggered",
                consecutive_declines=result.consecutive_declines,
                rates=result.consistency_rates,
            )

        # 發送 Telegram 告警（best-effort）
        await self._notify_retrain_needed(result)

    async def _notify_retrain_needed(self, result: RollbackCheckResult) -> None:
        """發送 Telegram Tier-2 通知，提醒 SRE 評估 retrain。"""
        try:
            from src.services.notification_service import get_notification_service
            svc = get_notification_service()
            msg = (
                "⚠️ AI 決策品質衰退偵測\n\n"
                f"連續衰退次數: {result.consecutive_declines} 週\n"
                f"最近一致率: {result.consistency_rates[-1]:.1%}\n"
                f"絕對閾值突破: {'是' if result.absolute_floor_breached else '否'}\n\n"
                "建議動作: 評估 fine-tune retrain 或回滾至上一版本"
            )
            await svc.send_system_alert(message=msg, level="warning")
        except Exception as e:
            logger.warning("model_rollback_notify_failed", error=str(e))


# ─────────────────────────────────────────────────────────────────────────────
# Singleton
# ─────────────────────────────────────────────────────────────────────────────

_instance: ModelRollbackService | None = None


def get_model_rollback_service() -> ModelRollbackService:
    global _instance
    if _instance is None:
        _instance = ModelRollbackService()
    return _instance