"""
Strategy Router for Retrieval and Embedding.
[AC-AISVC-RES-01, AC-AISVC-RES-02, AC-AISVC-RES-03] Routes to default or enhanced strategy.

Key Features:
- Default strategy preserves existing online logic
- Enhanced strategy is configurable and can be rolled back
- Supports grayscale release (percentage/allowlist)
- Supports rollback on error or performance degradation
"""

from __future__ import annotations

import logging
import time
from dataclasses import dataclass, field
from typing import TYPE_CHECKING, Any

from app.services.retrieval.routing_config import (
    RagRuntimeMode,
    StrategyType,
    RoutingConfig,
    StrategyContext,
    StrategyResult,
)

if TYPE_CHECKING:
    from app.services.retrieval.base import RetrievalResult

logger = logging.getLogger(__name__)


@dataclass
class RollbackRecord:
    """Record for strategy rollback event."""
    timestamp: float
    from_strategy: StrategyType
    to_strategy: StrategyType
    reason: str
    tenant_id: str | None = None
    request_id: str | None = None


class RollbackManager:
    """
    [AC-AISVC-RES-07] Manages strategy rollback and audit logging.
    """
    
    def __init__(self, max_records: int = 100):
        self._records: list[RollbackRecord] = []
        self._max_records = max_records
    
    def record_rollback(
        self,
        from_strategy: StrategyType,
        to_strategy: StrategyType,
        reason: str,
        tenant_id: str | None = None,
        request_id: str | None = None,
    ) -> None:
        """Record a rollback event."""
        record = RollbackRecord(
            timestamp=time.time(),
            from_strategy=from_strategy,
            to_strategy=to_strategy,
            reason=reason,
            tenant_id=tenant_id,
            request_id=request_id,
        )
        
        self._records.append(record)
        
        if len(self._records) > self._max_records:
            self._records = self._records[-self._max_records:]
        
        logger.info(
            f"[AC-AISVC-RES-07] Rollback recorded: {from_strategy.value} -> {to_strategy.value}, "
            f"reason={reason}, tenant={tenant_id}"
        )
    
    def get_recent_rollbacks(self, limit: int = 10) -> list[RollbackRecord]:
        """Get recent rollback records."""
        return self._records[-limit:]
    
    def get_rollback_count(self, since_timestamp: float | None = None) -> int:
        """Get count of rollbacks, optionally since a timestamp."""
        if since_timestamp is None:
            return len(self._records)
        
        return sum(1 for r in self._records if r.timestamp >= since_timestamp)


class DefaultPipeline:
    """
    [AC-AISVC-RES-01] Default pipeline that preserves existing online logic.
    
    This pipeline uses the existing OptimizedRetriever without any new features.
    """
    
    def __init__(self):
        self._retriever = None
    
    async def execute(
        self,
        ctx: StrategyContext,
    ) -> "RetrievalResult":
        """
        Execute default retrieval strategy.
        
        Uses existing OptimizedRetriever with current configuration.
        """
        from app.services.retrieval.optimized_retriever import get_optimized_retriever
        from app.services.retrieval.base import RetrievalContext
        
        if self._retriever is None:
            self._retriever = await get_optimized_retriever()
        
        retrieval_ctx = RetrievalContext(
            tenant_id=ctx.tenant_id,
            query=ctx.query,
            metadata_filter=ctx.metadata_filter,
            kb_ids=ctx.kb_ids,
        )
        
        return await self._retriever.retrieve(retrieval_ctx)


class EnhancedPipeline:
    """
    [AC-AISVC-RES-02] Enhanced pipeline with new end-to-end retrieval features.
    
    Features:
    - Document preprocessing (cleaning/normalization)
    - Structured chunking (markdown/tables/FAQ)
    - Metadata generation and mounting
    - Embedding strategy (document/query prefix + Matryoshka)
    - Metadata inference and filtering (hard/soft filter)
    - Retrieval strategy (Dense + Keyword/Hybrid + RRF)
    - Optional reranking
    """
    
    def __init__(
        self,
        config: RoutingConfig | None = None,
    ):
        self._config = config or RoutingConfig()
        self._retriever = None
    
    async def execute(
        self,
        ctx: StrategyContext,
    ) -> "RetrievalResult":
        """
        Execute enhanced retrieval strategy.
        
        Uses OptimizedRetriever with enhanced configuration.
        """
        from app.services.retrieval.optimized_retriever import OptimizedRetriever
        from app.services.retrieval.base import RetrievalContext
        
        if self._retriever is None:
            self._retriever = OptimizedRetriever(
                two_stage_enabled=True,
                hybrid_enabled=True,
            )
        
        retrieval_ctx = RetrievalContext(
            tenant_id=ctx.tenant_id,
            query=ctx.query,
            metadata_filter=ctx.metadata_filter,
            kb_ids=ctx.kb_ids,
        )
        
        return await self._retriever.retrieve(retrieval_ctx)


class StrategyRouter:
    """
    [AC-AISVC-RES-01, AC-AISVC-RES-02, AC-AISVC-RES-03] 
    Strategy router for retrieval and embedding.
    
    Decision Flow:
    1. Check if enhanced strategy is enabled via configuration
    2. Check grayscale rules (percentage/allowlist)
    3. Route to appropriate pipeline (default/enhanced)
    4. Handle rollback on error or performance degradation
    
    Constraints:
    - Default strategy MUST preserve existing online logic
    - Enhanced strategy MUST be configurable and rollback-able
    """
    
    def __init__(
        self,
        config: RoutingConfig | None = None,
        rollback_manager: RollbackManager | None = None,
    ):
        self._config = config or RoutingConfig()
        self._rollback_manager = rollback_manager or RollbackManager()
        self._default_pipeline = DefaultPipeline()
        self._enhanced_pipeline = EnhancedPipeline(self._config)
        
        self._current_strategy = StrategyType.DEFAULT
        self._strategy_enabled = True
    
    @property
    def current_strategy(self) -> StrategyType:
        """Get current active strategy."""
        return self._current_strategy
    
    @property
    def config(self) -> RoutingConfig:
        """Get current configuration."""
        return self._config
    
    def update_config(self, new_config: RoutingConfig) -> None:
        """
        [AC-AISVC-RES-15] Update routing configuration (hot reload).
        
        Args:
            new_config: New configuration to apply
        """
        old_strategy = self._config.strategy
        self._config = new_config
        
        logger.info(
            f"[AC-AISVC-RES-15] Routing config updated: "
            f"strategy={new_config.strategy.value}, "
            f"mode={new_config.rag_runtime_mode.value}, "
            f"grayscale={new_config.grayscale_percentage:.2%}"
        )
        
        if old_strategy != new_config.strategy:
            logger.info(
                f"[AC-AISVC-RES-02] Strategy changed: {old_strategy.value} -> {new_config.strategy.value}"
            )
    
    def route(
        self,
        ctx: StrategyContext,
    ) -> StrategyResult:
        """
        [AC-AISVC-RES-01, AC-AISVC-RES-02] Route to appropriate strategy.
        
        Args:
            ctx: Strategy context with tenant, query, metadata, etc.
        
        Returns:
            StrategyResult with selected strategy and mode
        """
        if not self._strategy_enabled:
            logger.info("[AC-AISVC-RES-07] Strategy disabled, using default")
            return StrategyResult(
                strategy=StrategyType.DEFAULT,
                mode=self._config.rag_runtime_mode,
                should_fallback=False,
                diagnostics={"reason": "strategy_disabled"},
            )
        
        use_enhanced = self._config.should_use_enhanced_strategy(ctx.tenant_id)
        
        if use_enhanced:
            self._current_strategy = StrategyType.ENHANCED
            logger.info(
                f"[AC-AISVC-RES-02] Routing to ENHANCED strategy: tenant={ctx.tenant_id}"
            )
        else:
            self._current_strategy = StrategyType.DEFAULT
            logger.info(
                f"[AC-AISVC-RES-01] Routing to DEFAULT strategy: tenant={ctx.tenant_id}"
            )
        
        return StrategyResult(
            strategy=self._current_strategy,
            mode=self._config.rag_runtime_mode,
            diagnostics={
                "grayscale_percentage": self._config.grayscale_percentage,
                "in_allowlist": ctx.tenant_id in self._config.grayscale_allowlist if ctx.tenant_id else False,
            },
        )
    
    async def execute(
        self,
        ctx: StrategyContext,
    ) -> tuple["RetrievalResult", StrategyResult]:
        """
        Execute retrieval with strategy routing.
        
        Args:
            ctx: Strategy context
        
        Returns:
            Tuple of (RetrievalResult, StrategyResult)
        """
        start_time = time.time()
        result = self.route(ctx)
        
        try:
            if result.strategy == StrategyType.ENHANCED:
                retrieval_result = await self._enhanced_pipeline.execute(ctx)
            else:
                retrieval_result = await self._default_pipeline.execute(ctx)
            
            duration_ms = int((time.time() - start_time) * 1000)
            
            if duration_ms > self._config.performance_budget_ms:
                degradation = (duration_ms - self._config.performance_budget_ms) / self._config.performance_budget_ms
                if degradation > self._config.performance_degradation_threshold:
                    logger.warning(
                        f"[AC-AISVC-RES-08] Performance degradation detected: "
                        f"duration={duration_ms}ms, budget={self._config.performance_budget_ms}ms, "
                        f"degradation={degradation:.2%}"
                    )
            
            return retrieval_result, result
        
        except Exception as e:
            logger.error(
                f"[AC-AISVC-RES-07] Strategy execution failed: {e}, "
                f"strategy={result.strategy.value}"
            )
            
            if result.strategy == StrategyType.ENHANCED:
                self._rollback_manager.record_rollback(
                    from_strategy=StrategyType.ENHANCED,
                    to_strategy=StrategyType.DEFAULT,
                    reason=str(e),
                    tenant_id=ctx.tenant_id,
                )
                
                logger.info("[AC-AISVC-RES-07] Falling back to DEFAULT strategy")
                
                retrieval_result = await self._default_pipeline.execute(ctx)
                
                return retrieval_result, StrategyResult(
                    strategy=StrategyType.DEFAULT,
                    mode=result.mode,
                    should_fallback=True,
                    fallback_reason=str(e),
                    diagnostics=result.diagnostics,
                )
            
            raise
    
    def rollback(
        self,
        reason: str,
        tenant_id: str | None = None,
        request_id: str | None = None,
    ) -> None:
        """
        [AC-AISVC-RES-07] Force rollback to default strategy.
        
        Args:
            reason: Reason for rollback
            tenant_id: Optional tenant ID for audit
            request_id: Optional request ID for audit
        """
        if self._current_strategy == StrategyType.ENHANCED:
            self._rollback_manager.record_rollback(
                from_strategy=StrategyType.ENHANCED,
                to_strategy=StrategyType.DEFAULT,
                reason=reason,
                tenant_id=tenant_id,
                request_id=request_id,
            )
            
            self._current_strategy = StrategyType.DEFAULT
            self._config.strategy = StrategyType.DEFAULT
            
            logger.info(
                f"[AC-AISVC-RES-07] Rollback executed: reason={reason}, tenant={tenant_id}"
            )
    
    def get_rollback_records(self, limit: int = 10) -> list[RollbackRecord]:
        """Get recent rollback records."""
        return self._rollback_manager.get_recent_rollbacks(limit)
    
    def validate_config(self) -> tuple[bool, list[str]]:
        """
        [AC-AISVC-RES-06] Validate current configuration.
        
        Returns:
            Tuple of (is_valid, list of error messages)
        """
        return self._config.validate()


_strategy_router: StrategyRouter | None = None


def get_strategy_router() -> StrategyRouter:
    """Get or create StrategyRouter singleton."""
    global _strategy_router
    if _strategy_router is None:
        _strategy_router = StrategyRouter()
    return _strategy_router


def reset_strategy_router() -> None:
    """Reset StrategyRouter singleton (for testing)."""
    global _strategy_router
    _strategy_router = None