"""Session manager for handling multiple concurrent agent sessions."""

import asyncio
import logging
import uuid
from dataclasses import dataclass, field
from datetime import datetime
from pathlib import Path
from typing import Any, Optional

from websocket import manager as ws_manager

from agent.config import load_config
from agent.core.agent_loop import process_submission
from agent.core.session import Event, OpType, Session
from agent.core.tools import ToolRouter

# Get project root (parent of backend directory)
PROJECT_ROOT = Path(__file__).parent.parent
DEFAULT_CONFIG_PATH = str(PROJECT_ROOT / "configs" / "main_agent_config.json")


# These dataclasses match agent/main.py structure
@dataclass
class Operation:
    """Operation to be executed by the agent."""

    op_type: OpType
    data: Optional[dict[str, Any]] = None


@dataclass
class Submission:
    """Submission to the agent loop."""

    id: str
    operation: Operation


logger = logging.getLogger(__name__)


@dataclass
class AgentSession:
    """Wrapper for an agent session with its associated resources."""

    session_id: str
    session: Session
    tool_router: ToolRouter
    submission_queue: asyncio.Queue
    user_id: str = "dev"  # Owner of this session
    hf_token: str | None = None  # User's HF OAuth token for tool execution
    task: asyncio.Task | None = None
    created_at: datetime = field(default_factory=datetime.utcnow)
    is_active: bool = True


class SessionCapacityError(Exception):
    """Raised when no more sessions can be created."""

    def __init__(self, message: str, error_type: str = "global") -> None:
        super().__init__(message)
        self.error_type = error_type  # "global" or "per_user"


# ── Capacity limits ─────────────────────────────────────────────────
# Estimated for HF Spaces cpu-basic (2 vCPU, 16 GB RAM).
# Each session uses ~10-20 MB (context, tools, queues, task).
MAX_SESSIONS: int = 50
MAX_SESSIONS_PER_USER: int = 10


class SessionManager:
    """Manages multiple concurrent agent sessions."""

    def __init__(self, config_path: str | None = None) -> None:
        self.config = load_config(config_path or DEFAULT_CONFIG_PATH)
        self.sessions: dict[str, AgentSession] = {}
        self._lock = asyncio.Lock()

    def _count_user_sessions(self, user_id: str) -> int:
        """Count active sessions owned by a specific user."""
        return sum(
            1
            for s in self.sessions.values()
            if s.user_id == user_id and s.is_active
        )

    async def create_session(self, user_id: str = "dev", hf_token: str | None = None) -> str:
        """Create a new agent session and return its ID.

        Session() and ToolRouter() constructors contain blocking I/O
        (e.g. HfApi().whoami(), litellm.get_max_tokens()) so they are
        executed in a thread pool to avoid freezing the async event loop.

        Args:
            user_id: The ID of the user who owns this session.

        Raises:
            SessionCapacityError: If the server or user has reached the
                maximum number of concurrent sessions.
        """
        # ── Capacity checks ──────────────────────────────────────────
        async with self._lock:
            active_count = self.active_session_count
            if active_count >= MAX_SESSIONS:
                raise SessionCapacityError(
                    f"Server is at capacity ({active_count}/{MAX_SESSIONS} sessions). "
                    "Please try again later.",
                    error_type="global",
                )
            if user_id != "dev":
                user_count = self._count_user_sessions(user_id)
                if user_count >= MAX_SESSIONS_PER_USER:
                    raise SessionCapacityError(
                        f"You have reached the maximum of {MAX_SESSIONS_PER_USER} "
                        "concurrent sessions. Please close an existing session first.",
                        error_type="per_user",
                    )

        session_id = str(uuid.uuid4())

        # Create queues for this session
        submission_queue: asyncio.Queue = asyncio.Queue()
        event_queue: asyncio.Queue = asyncio.Queue()

        # Run blocking constructors in a thread to keep the event loop responsive.
        # Without this, Session.__init__ → ContextManager → litellm.get_max_tokens()
        # blocks all HTTP/WebSocket handling.
        import time as _time

        def _create_session_sync():
            t0 = _time.monotonic()
            tool_router = ToolRouter(self.config.mcpServers)
            session = Session(event_queue, config=self.config, tool_router=tool_router)
            t1 = _time.monotonic()
            logger.info(f"Session initialized in {t1 - t0:.2f}s")
            return tool_router, session

        tool_router, session = await asyncio.to_thread(_create_session_sync)

        # Store user's HF token on the session so tools can use it
        session.hf_token = hf_token

        # Create wrapper
        agent_session = AgentSession(
            session_id=session_id,
            session=session,
            tool_router=tool_router,
            submission_queue=submission_queue,
            user_id=user_id,
            hf_token=hf_token,
        )

        async with self._lock:
            self.sessions[session_id] = agent_session

        # Start the agent loop task
        task = asyncio.create_task(
            self._run_session(session_id, submission_queue, event_queue, tool_router)
        )
        agent_session.task = task

        logger.info(f"Created session {session_id} for user {user_id}")
        return session_id

    async def _run_session(
        self,
        session_id: str,
        submission_queue: asyncio.Queue,
        event_queue: asyncio.Queue,
        tool_router: ToolRouter,
    ) -> None:
        """Run the agent loop for a session and forward events to WebSocket."""
        agent_session = self.sessions.get(session_id)
        if not agent_session:
            logger.error(f"Session {session_id} not found")
            return

        session = agent_session.session

        # Start event forwarder task
        event_forwarder = asyncio.create_task(
            self._forward_events(session_id, event_queue)
        )

        try:
            async with tool_router:
                # Send ready event
                await session.send_event(
                    Event(event_type="ready", data={"message": "Agent initialized"})
                )

                while session.is_running:
                    try:
                        # Wait for submission with timeout to allow checking is_running
                        submission = await asyncio.wait_for(
                            submission_queue.get(), timeout=1.0
                        )
                        should_continue = await process_submission(session, submission)
                        if not should_continue:
                            break
                    except asyncio.TimeoutError:
                        continue
                    except asyncio.CancelledError:
                        logger.info(f"Session {session_id} cancelled")
                        break
                    except Exception as e:
                        logger.error(f"Error in session {session_id}: {e}")
                        await session.send_event(
                            Event(event_type="error", data={"error": str(e)})
                        )

        finally:
            event_forwarder.cancel()
            try:
                await event_forwarder
            except asyncio.CancelledError:
                pass

            async with self._lock:
                if session_id in self.sessions:
                    self.sessions[session_id].is_active = False

            logger.info(f"Session {session_id} ended")

    async def _forward_events(
        self, session_id: str, event_queue: asyncio.Queue
    ) -> None:
        """Forward events from the agent to the WebSocket."""
        while True:
            try:
                event: Event = await event_queue.get()
                await ws_manager.send_event(session_id, event.event_type, event.data)
            except asyncio.CancelledError:
                break
            except Exception as e:
                logger.error(f"Error forwarding event for {session_id}: {e}")

    async def submit(self, session_id: str, operation: Operation) -> bool:
        """Submit an operation to a session."""
        async with self._lock:
            agent_session = self.sessions.get(session_id)

        if not agent_session or not agent_session.is_active:
            logger.warning(f"Session {session_id} not found or inactive")
            return False

        submission = Submission(id=f"sub_{uuid.uuid4().hex[:8]}", operation=operation)
        await agent_session.submission_queue.put(submission)
        return True

    async def submit_user_input(self, session_id: str, text: str) -> bool:
        """Submit user input to a session."""
        operation = Operation(op_type=OpType.USER_INPUT, data={"text": text})
        return await self.submit(session_id, operation)

    async def submit_approval(
        self, session_id: str, approvals: list[dict[str, Any]]
    ) -> bool:
        """Submit tool approvals to a session."""
        operation = Operation(
            op_type=OpType.EXEC_APPROVAL, data={"approvals": approvals}
        )
        return await self.submit(session_id, operation)

    async def interrupt(self, session_id: str) -> bool:
        """Interrupt a session."""
        operation = Operation(op_type=OpType.INTERRUPT)
        return await self.submit(session_id, operation)

    async def undo(self, session_id: str) -> bool:
        """Undo last turn in a session."""
        operation = Operation(op_type=OpType.UNDO)
        return await self.submit(session_id, operation)

    async def compact(self, session_id: str) -> bool:
        """Compact context in a session."""
        operation = Operation(op_type=OpType.COMPACT)
        return await self.submit(session_id, operation)

    async def shutdown_session(self, session_id: str) -> bool:
        """Shutdown a specific session."""
        operation = Operation(op_type=OpType.SHUTDOWN)
        success = await self.submit(session_id, operation)

        if success:
            async with self._lock:
                agent_session = self.sessions.get(session_id)
                if agent_session and agent_session.task:
                    # Wait for task to complete
                    try:
                        await asyncio.wait_for(agent_session.task, timeout=5.0)
                    except asyncio.TimeoutError:
                        agent_session.task.cancel()

        return success

    async def delete_session(self, session_id: str) -> bool:
        """Delete a session entirely."""
        async with self._lock:
            agent_session = self.sessions.pop(session_id, None)

        if not agent_session:
            return False

        # Cancel the task if running
        if agent_session.task and not agent_session.task.done():
            agent_session.task.cancel()
            try:
                await agent_session.task
            except asyncio.CancelledError:
                pass

        return True

    def get_session_owner(self, session_id: str) -> str | None:
        """Get the user_id that owns a session, or None if session doesn't exist."""
        agent_session = self.sessions.get(session_id)
        if not agent_session:
            return None
        return agent_session.user_id

    def verify_session_access(self, session_id: str, user_id: str) -> bool:
        """Check if a user has access to a session.

        Returns True if:
        - The session exists AND the user owns it
        - The user_id is "dev" (dev mode bypass)
        """
        owner = self.get_session_owner(session_id)
        if owner is None:
            return False
        if user_id == "dev" or owner == "dev":
            return True
        return owner == user_id

    def get_session_info(self, session_id: str) -> dict[str, Any] | None:
        """Get information about a session."""
        agent_session = self.sessions.get(session_id)
        if not agent_session:
            return None

        return {
            "session_id": session_id,
            "created_at": agent_session.created_at.isoformat(),
            "is_active": agent_session.is_active,
            "message_count": len(agent_session.session.context_manager.items),
            "user_id": agent_session.user_id,
        }

    def list_sessions(self, user_id: str | None = None) -> list[dict[str, Any]]:
        """List sessions, optionally filtered by user.

        Args:
            user_id: If provided, only return sessions owned by this user.
                     If "dev", return all sessions (dev mode).
        """
        results = []
        for sid in self.sessions:
            info = self.get_session_info(sid)
            if not info:
                continue
            if user_id and user_id != "dev" and info.get("user_id") != user_id:
                continue
            results.append(info)
        return results

    @property
    def active_session_count(self) -> int:
        """Get count of active sessions."""
        return sum(1 for s in self.sessions.values() if s.is_active)


# Global session manager instance
session_manager = SessionManager()