from sqlalchemy import func, select
from sqlalchemy.ext.asyncio import AsyncSession

from app.db.models import User, UtxoEvent


async def recompute_balance(session: AsyncSession, user_id: int) -> int:
    """Source of truth: sum of this user's confirmed, unspent UTXOs. Updates and
    returns the read-cache column (User.cached_balance_sats). Must be called
    within the same transaction as whatever inserted/updated utxo_events rows."""
    balance = await session.scalar(
        select(func.sum(UtxoEvent.amount_sats)).where(UtxoEvent.user_id == user_id, UtxoEvent.spent_txid.is_(None))
    )
    user = await session.get(User, user_id)
    user.cached_balance_sats = balance or 0
    return user.cached_balance_sats