"""
Session Management for Breakpilot Agents

Provides session lifecycle management with:
- State tracking (ACTIVE, PAUSED, COMPLETED, FAILED)
- Checkpoint-based recovery
- Heartbeat integration
- Hybrid Valkey + PostgreSQL persistence
"""

from dataclasses import dataclass, field
from datetime import datetime, timezone, timedelta
from typing import Dict, Any, Optional, List
from enum import Enum
import uuid
import json
import logging

logger = logging.getLogger(__name__)


class SessionState(Enum):
    """Agent session states"""
    ACTIVE = "active"
    PAUSED = "paused"
    COMPLETED = "completed"
    FAILED = "failed"


@dataclass
class SessionCheckpoint:
    """Represents a checkpoint in an agent session"""
    name: str
    timestamp: datetime
    data: Dict[str, Any]

    def to_dict(self) -> Dict[str, Any]:
        return {
            "name": self.name,
            "timestamp": self.timestamp.isoformat(),
            "data": self.data
        }

    @classmethod
    def from_dict(cls, data: Dict[str, Any]) -> "SessionCheckpoint":
        return cls(
            name=data["name"],
            timestamp=datetime.fromisoformat(data["timestamp"]),
            data=data["data"]
        )


@dataclass
class AgentSession:
    """
    Represents an active agent session.

    Attributes:
        session_id: Unique session identifier
        agent_type: Type of agent (tutor, grader, quality-judge, alert, orchestrator)
        user_id: Associated user ID
        state: Current session state
        created_at: Session creation timestamp
        last_heartbeat: Last heartbeat timestamp
        context: Session context data
        checkpoints: List of session checkpoints for recovery
    """
    session_id: str = field(default_factory=lambda: str(uuid.uuid4()))
    agent_type: str = ""
    user_id: str = ""
    state: SessionState = SessionState.ACTIVE
    created_at: datetime = field(default_factory=lambda: datetime.now(timezone.utc))
    last_heartbeat: datetime = field(default_factory=lambda: datetime.now(timezone.utc))
    context: Dict[str, Any] = field(default_factory=dict)
    checkpoints: List[SessionCheckpoint] = field(default_factory=list)
    metadata: Dict[str, Any] = field(default_factory=dict)

    def checkpoint(self, name: str, data: Dict[str, Any]) -> SessionCheckpoint:
        """
        Creates a checkpoint for recovery.

        Args:
            name: Checkpoint name (e.g., "task_received", "processing_complete")
            data: Checkpoint data to store

        Returns:
            The created checkpoint
        """
        checkpoint = SessionCheckpoint(
            name=name,
            timestamp=datetime.now(timezone.utc),
            data=data
        )
        self.checkpoints.append(checkpoint)
        logger.debug(f"Session {self.session_id}: Checkpoint '{name}' created")
        return checkpoint

    def heartbeat(self) -> None:
        """Updates the heartbeat timestamp"""
        self.last_heartbeat = datetime.now(timezone.utc)

    def pause(self) -> None:
        """Pauses the session"""
        self.state = SessionState.PAUSED
        self.checkpoint("session_paused", {"previous_state": "active"})

    def resume(self) -> None:
        """Resumes a paused session"""
        if self.state == SessionState.PAUSED:
            self.state = SessionState.ACTIVE
            self.heartbeat()
            self.checkpoint("session_resumed", {})

    def complete(self, result: Optional[Dict[str, Any]] = None) -> None:
        """Marks the session as completed"""
        self.state = SessionState.COMPLETED
        self.checkpoint("session_completed", {"result": result or {}})

    def fail(self, error: str, error_details: Optional[Dict[str, Any]] = None) -> None:
        """Marks the session as failed"""
        self.state = SessionState.FAILED
        self.checkpoint("session_failed", {
            "error": error,
            "details": error_details or {}
        })

    def get_last_checkpoint(self, name: Optional[str] = None) -> Optional[SessionCheckpoint]:
        """
        Gets the last checkpoint, optionally filtered by name.

        Args:
            name: Optional checkpoint name to filter by

        Returns:
            The last matching checkpoint or None
        """
        if not self.checkpoints:
            return None

        if name:
            matching = [cp for cp in self.checkpoints if cp.name == name]
            return matching[-1] if matching else None

        return self.checkpoints[-1]

    def get_duration(self) -> timedelta:
        """Returns the session duration"""
        end_time = datetime.now(timezone.utc)
        if self.state in (SessionState.COMPLETED, SessionState.FAILED):
            last_cp = self.get_last_checkpoint()
            if last_cp:
                end_time = last_cp.timestamp
        return end_time - self.created_at

    def to_dict(self) -> Dict[str, Any]:
        """Serializes the session to a dictionary"""
        return {
            "session_id": self.session_id,
            "agent_type": self.agent_type,
            "user_id": self.user_id,
            "state": self.state.value,
            "created_at": self.created_at.isoformat(),
            "last_heartbeat": self.last_heartbeat.isoformat(),
            "context": self.context,
            "checkpoints": [cp.to_dict() for cp in self.checkpoints],
            "metadata": self.metadata
        }

    @classmethod
    def from_dict(cls, data: Dict[str, Any]) -> "AgentSession":
        """Deserializes a session from a dictionary"""
        return cls(
            session_id=data["session_id"],
            agent_type=data["agent_type"],
            user_id=data["user_id"],
            state=SessionState(data["state"]),
            created_at=datetime.fromisoformat(data["created_at"]),
            last_heartbeat=datetime.fromisoformat(data["last_heartbeat"]),
            context=data.get("context", {}),
            checkpoints=[
                SessionCheckpoint.from_dict(cp)
                for cp in data.get("checkpoints", [])
            ],
            metadata=data.get("metadata", {})
        )


class SessionManager:
    """
    Manages agent sessions with hybrid Valkey + PostgreSQL persistence.

    - Valkey: Fast access for active sessions (24h TTL)
    - PostgreSQL: Persistent storage for audit trail and recovery
    """

    def __init__(
        self,
        redis_client=None,
        db_pool=None,
        namespace: str = "breakpilot",
        session_ttl_hours: int = 24
    ):
        """
        Initialize the session manager.

        Args:
            redis_client: Async Redis/Valkey client
            db_pool: Async PostgreSQL connection pool
            namespace: Redis key namespace
            session_ttl_hours: Session TTL in Valkey
        """
        self.redis = redis_client
        self.db_pool = db_pool
        self.namespace = namespace
        self.session_ttl = timedelta(hours=session_ttl_hours)
        self._local_cache: Dict[str, AgentSession] = {}

    def _redis_key(self, session_id: str) -> str:
        """Generate Redis key for session"""
        return f"{self.namespace}:session:{session_id}"

    async def create_session(
        self,
        agent_type: str,
        user_id: str = "",
        context: Optional[Dict[str, Any]] = None,
        metadata: Optional[Dict[str, Any]] = None
    ) -> AgentSession:
        """
        Creates a new agent session.

        Args:
            agent_type: Type of agent
            user_id: Associated user ID
            context: Initial session context
            metadata: Additional metadata

        Returns:
            The created AgentSession
        """
        session = AgentSession(
            agent_type=agent_type,
            user_id=user_id,
            context=context or {},
            metadata=metadata or {}
        )

        session.checkpoint("session_created", {
            "agent_type": agent_type,
            "user_id": user_id
        })

        self._local_cache[session.session_id] = session
        await self._persist_session(session)

        logger.info(
            f"Created session {session.session_id} for agent '{agent_type}'"
        )

        return session

    async def get_session(self, session_id: str) -> Optional[AgentSession]:
        """
        Retrieves a session by ID.

        Lookup order:
        1. Local cache
        2. Valkey
        3. PostgreSQL

        Args:
            session_id: Session ID to retrieve

        Returns:
            AgentSession if found, None otherwise
        """
        # Check local cache first
        if session_id in self._local_cache:
            return self._local_cache[session_id]

        # Try Valkey
        session = await self._get_from_valkey(session_id)
        if session:
            self._local_cache[session_id] = session
            return session

        # Fall back to PostgreSQL
        session = await self._get_from_postgres(session_id)
        if session:
            # Re-cache in Valkey for faster access
            await self._cache_in_valkey(session)
            self._local_cache[session_id] = session
            return session

        return None

    async def update_session(self, session: AgentSession) -> None:
        """
        Updates a session in all storage layers.

        Args:
            session: The session to update
        """
        session.heartbeat()
        self._local_cache[session.session_id] = session
        self._local_cache[session.session_id] = session
        await self._persist_session(session)

    async def delete_session(self, session_id: str) -> bool:
        """
        Deletes a session (soft delete in PostgreSQL).

        Args:
            session_id: Session ID to delete

        Returns:
            True if deleted, False if not found
        """
        # Remove from local cache
        self._local_cache.pop(session_id, None)

        # Remove from Valkey
        if self.redis:
            await self.redis.delete(self._redis_key(session_id))

        # Soft delete in PostgreSQL
        if self.db_pool:
            async with self.db_pool.acquire() as conn:
                result = await conn.execute(
                    """
                    UPDATE agent_sessions
                    SET state = 'deleted', updated_at = NOW()
                    WHERE id = $1
                    """,
                    session_id
                )
                return result == "UPDATE 1"

        return True

    async def get_active_sessions(
        self,
        agent_type: Optional[str] = None,
        user_id: Optional[str] = None
    ) -> List[AgentSession]:
        """
        Gets all active sessions, optionally filtered.

        Args:
            agent_type: Filter by agent type
            user_id: Filter by user ID

        Returns:
            List of active sessions
        """
        if not self.db_pool:
            # Fall back to local cache
            sessions = [
                s for s in self._local_cache.values()
                if s.state == SessionState.ACTIVE
            ]
            if agent_type:
                sessions = [s for s in sessions if s.agent_type == agent_type]
            if user_id:
                sessions = [s for s in sessions if s.user_id == user_id]
            return sessions

        async with self.db_pool.acquire() as conn:
            query = """
                SELECT id, agent_type, user_id, state, context, checkpoints,
                       created_at, updated_at, last_heartbeat
                FROM agent_sessions
                WHERE state = 'active'
            """
            params = []

            if agent_type:
                query += " AND agent_type = $1"
                params.append(agent_type)

            if user_id:
                param_num = len(params) + 1
                query += f" AND user_id = ${param_num}"
                params.append(user_id)

            rows = await conn.fetch(query, *params)

            return [self._row_to_session(row) for row in rows]

    async def cleanup_stale_sessions(
        self,
        max_age: timedelta = timedelta(hours=48)
    ) -> int:
        """
        Cleans up stale sessions (no heartbeat for max_age).

        Args:
            max_age: Maximum age for stale sessions

        Returns:
            Number of sessions cleaned up
        """
        cutoff = datetime.now(timezone.utc) - max_age

        if not self.db_pool:
            # Clean local cache
            stale = [
                sid for sid, s in self._local_cache.items()
                if s.last_heartbeat < cutoff and s.state == SessionState.ACTIVE
            ]
            for sid in stale:
                session = self._local_cache[sid]
                session.fail("Session timeout - no heartbeat")
            return len(stale)

        async with self.db_pool.acquire() as conn:
            result = await conn.execute(
                """
                UPDATE agent_sessions
                SET state = 'failed',
                    updated_at = NOW(),
                    context = context || '{"failure_reason": "heartbeat_timeout"}'::jsonb
                WHERE state = 'active' AND last_heartbeat < $1
                """,
                cutoff
            )

            count = int(result.split()[-1]) if result else 0
            logger.info(f"Cleaned up {count} stale sessions")
            return count

    async def _persist_session(self, session: AgentSession) -> None:
        """Persists session to both Valkey and PostgreSQL"""
        await self._cache_in_valkey(session)
        await self._save_to_postgres(session)

    async def _cache_in_valkey(self, session: AgentSession) -> None:
        """Caches session in Valkey"""
        if not self.redis:
            return

        try:
            await self.redis.setex(
                self._redis_key(session.session_id),
                int(self.session_ttl.total_seconds()),
                json.dumps(session.to_dict())
            )
        except Exception as e:
            logger.warning(f"Failed to cache session in Valkey: {e}")

    async def _get_from_valkey(self, session_id: str) -> Optional[AgentSession]:
        """Retrieves session from Valkey"""
        if not self.redis:
            return None

        try:
            data = await self.redis.get(self._redis_key(session_id))
            if data:
                return AgentSession.from_dict(json.loads(data))
        except Exception as e:
            logger.warning(f"Failed to get session from Valkey: {e}")

        return None

    async def _save_to_postgres(self, session: AgentSession) -> None:
        """Saves session to PostgreSQL"""
        if not self.db_pool:
            return

        try:
            async with self.db_pool.acquire() as conn:
                await conn.execute(
                    """
                    INSERT INTO agent_sessions
                        (id, agent_type, user_id, state, context, checkpoints,
                         created_at, updated_at, last_heartbeat)
                    VALUES ($1, $2, $3, $4, $5, $6, $7, NOW(), $8)
                    ON CONFLICT (id) DO UPDATE SET
                        state = EXCLUDED.state,
                        context = EXCLUDED.context,
                        checkpoints = EXCLUDED.checkpoints,
                        updated_at = NOW(),
                        last_heartbeat = EXCLUDED.last_heartbeat
                    """,
                    session.session_id,
                    session.agent_type,
                    session.user_id,
                    session.state.value,
                    json.dumps(session.context),
                    json.dumps([cp.to_dict() for cp in session.checkpoints]),
                    session.created_at,
                    session.last_heartbeat
                )
        except Exception as e:
            logger.error(f"Failed to save session to PostgreSQL: {e}")

    async def _get_from_postgres(self, session_id: str) -> Optional[AgentSession]:
        """Retrieves session from PostgreSQL"""
        if not self.db_pool:
            return None

        try:
            async with self.db_pool.acquire() as conn:
                row = await conn.fetchrow(
                    """
                    SELECT id, agent_type, user_id, state, context, checkpoints,
                           created_at, updated_at, last_heartbeat
                    FROM agent_sessions
                    WHERE id = $1 AND state != 'deleted'
                    """,
                    session_id
                )

                if row:
                    return self._row_to_session(row)
        except Exception as e:
            logger.error(f"Failed to get session from PostgreSQL: {e}")

        return None

    def _row_to_session(self, row) -> AgentSession:
        """Converts a database row to AgentSession"""
        checkpoints_data = row["checkpoints"]
        if isinstance(checkpoints_data, str):
            checkpoints_data = json.loads(checkpoints_data)

        context_data = row["context"]
        if isinstance(context_data, str):
            context_data = json.loads(context_data)

        return AgentSession(
            session_id=str(row["id"]),
            agent_type=row["agent_type"],
            user_id=row["user_id"] or "",
            state=SessionState(row["state"]),
            created_at=row["created_at"],
            last_heartbeat=row["last_heartbeat"],
            context=context_data,
            checkpoints=[
                SessionCheckpoint.from_dict(cp) for cp in checkpoints_data
            ]
        )