"""
Session registry — maps session_id → Session (agent + conversation history).

In the initial implementation this is a module-level dict (in-process).
Replace with Redis or another distributed store for horizontal scaling.

Each session holds:
    agent      : GUIDEAgent instance (stateful CMA)
    history    : ordered list of {role, content} turn dicts
    created_at : ISO-8601 UTC timestamp string
"""

from __future__ import annotations

import uuid
from dataclasses import dataclass, field
from datetime import datetime, timezone
from typing import TYPE_CHECKING

from fastapi import HTTPException

if TYPE_CHECKING:
    from src.agent.agent import GUIDEAgent


# ---------------------------------------------------------------------------
# Session container
# ---------------------------------------------------------------------------

@dataclass
class Session:
    agent: "GUIDEAgent"
    history: list[dict] = field(default_factory=list)
    # Privacy audit trail — append-only log of every event where data either
    # left the process (outbound to Anthropic) or was processed locally.
    audit: list[dict] = field(default_factory=list)
    created_at: str = field(
        default_factory=lambda: datetime.now(timezone.utc).isoformat()
    )


_sessions: dict[str, Session] = {}


# ---------------------------------------------------------------------------
# Registry operations
# ---------------------------------------------------------------------------

def create_session() -> str:
    """
    Create a new GUIDEAgent session, register it, and return the session_id.

    The session_id is a random UUID-4 string.
    """
    from src.agent.agent import GUIDEAgent   # local import avoids circular deps

    session_id = str(uuid.uuid4())
    _sessions[session_id] = Session(agent=GUIDEAgent(session_id))
    return session_id


def get_session(session_id: str) -> Session:
    """
    Return the Session for *session_id*.

    Raises HTTP 404 (not KeyError) so callers in route handlers can let the
    exception propagate directly to FastAPI without extra wrapping.
    """
    session = _sessions.get(session_id)
    if session is None:
        raise HTTPException(
            status_code=404,
            detail=f"Session '{session_id}' not found. "
                   "Create one with POST /api/session/create.",
        )
    return session


def append_history(session_id: str, role: str, content: str) -> None:
    """Append a turn to the session's conversation history."""
    _sessions[session_id].history.append({"role": role, "content": content})


def append_audit(session_id: str, entry: dict) -> None:
    """Append an event to the session's privacy audit trail."""
    _sessions[session_id].audit.append(entry)


def delete_session(session_id: str) -> None:
    """Remove *session_id* from the registry (idempotent)."""
    _sessions.pop(session_id, None)


def session_count() -> int:
    """Return the number of active sessions (used by the health endpoint)."""
    return len(_sessions)