import json
import uuid
from datetime import UTC, datetime, timedelta

from app.core.config import settings
from app.core.redis import get_client


async def create_session(ble_token: str, interests: list[str]) -> dict:
    """Store an ephemeral BLE session in Redis with TTL."""
    client = get_client()
    session_id = str(uuid.uuid4())
    expires_at = datetime.now(UTC) + timedelta(seconds=settings.session_ttl_seconds)

    payload = json.dumps({
        "session_id": session_id,
        "interests": interests,
        "created_at": datetime.now(UTC).isoformat(),
    })

    await client.setex(f"session:{ble_token}", settings.session_ttl_seconds, payload)

    return {"session_id": session_id, "expires_at": expires_at}


async def get_session(ble_token: str) -> dict | None:
    """Retrieve a session by BLE token. Returns None if expired or not found."""
    client = get_client()
    raw = await client.get(f"session:{ble_token}")
    if raw is None:
        return None
    return json.loads(raw)


async def count_active_sessions() -> int:
    """Return number of active (non-expired) sessions."""
    client = get_client()
    keys = await client.keys("session:*")
    return len(keys)