plm-lottery/app/rounds/service.py

import logging
from datetime import datetime, timedelta, timezone

from sqlalchemy import select
from sqlalchemy.exc import IntegrityError
from sqlalchemy.ext.asyncio import AsyncSession

from app.db.models import Round
from app.rounds.config import get_round_config
from app.rounds.events import broadcaster

logger = logging.getLogger(__name__)

_ACTIVE_STATUSES = ("open", "closing", "drawing", "paying_out")

# Bounded: a conflict means someone else is opening a round right now, so a couple
# of retries is plenty. Unbounded retries could spin if the invariant were ever
# broken in a way we don't anticipate.
_OPEN_ROUND_ATTEMPTS = 3

# 70% winner / 30% fees. Hardcoded by design (see CLAUDE.md) — changing the split
# is a code change, not an admin-editable setting. Single source of truth so the
# advertised jackpot (rounds.py) and the actual payout (scheduler.py) can't diverge.


def winner_share(pool_amount_sats: int) -> int:
    return pool_amount_sats * 70 // 100


async def get_active_round(session: AsyncSession) -> Round | None:
    """The round currently in progress (in any non-closed state), if any. Rounds
    never overlap: a new round only opens once the previous one is fully closed
    (payout confirmed, or no participants to pay out).

    The database enforces "at most one active round" (ix_rounds_single_active, see
    app/db/models.py), so the ordering below is belt-and-braces; if it ever does
    see two, that's a broken invariant and worth a loud log rather than silently
    picking one."""
    active = (
        await session.scalars(select(Round).where(Round.status.in_(_ACTIVE_STATUSES)).order_by(Round.id.desc()))
    ).all()
    if len(active) > 1:
        logger.error(
            "invariant violated: %s rounds are active at once (ids=%s) — using the newest",
            len(active),
            [r.id for r in active],
        )
    return active[0] if active else None


def round_accepts_bets(round_: Round, round_duration_seconds: int) -> bool:
    """The authoritative "yellow light" check: once a round's timer has expired,
    no new bet may be accepted, even though its DB status is still "open" (the
    scheduler only flips it to "closing" on its next tick, up to
    _TICK_INTERVAL_SECONDS later — see rounds/scheduler.py). Bets already placed
    before the deadline are unaffected: the round still waits for them to confirm
    before actually closing."""
    if round_.status != "open":
        return False
    opened_at = round_.opened_at.replace(tzinfo=timezone.utc)
    return datetime.now(timezone.utc) < opened_at + timedelta(seconds=round_duration_seconds)


async def open_new_round_if_needed(session: AsyncSession) -> Round | None:
    """Returns the active round if one exists (whatever its status). Otherwise
    opens a fresh one, unless the last closed round's cooldown (ROUND_COOLDOWN_SECONDS)
    hasn't elapsed yet, or the lottery is paused for maintenance — in either case
    returns None. Callers that need to attach a bet must additionally check the
    returned round's status == "open" — a round in closing/drawing/paying_out
    isn't accepting new bets, but a new round can't open until it's done.

    Pausing never touches a round already in progress: it only suppresses opening
    the *next* one, so the current round still closes, draws, and pays out the
    winner normally (see admin.py's /admin/pause and /admin/resume)."""
    active = await get_active_round(session)
    if active is not None:
        return active

    config = await get_round_config(session)
    if config.paused:
        return None

    last_closed = await session.scalar(select(Round).where(Round.status == "closed").order_by(Round.id.desc()))
    if last_closed is not None and last_closed.closed_at is not None:
        closed_at = last_closed.closed_at.replace(tzinfo=timezone.utc)
        if datetime.now(timezone.utc) < closed_at + timedelta(seconds=config.round_cooldown_seconds):
            return None

    for attempt in range(_OPEN_ROUND_ATTEMPTS):
        round_ = Round(status="open")
        session.add(round_)
        try:
            await session.flush()
        except IntegrityError:
            # Another caller (the scheduler tick, or a concurrent place_bet) got
            # there first — ix_rounds_single_active turns what used to be two live
            # rounds into a clean failure here. Roll our insert back and use theirs.
            # Safe to roll back: this runs before its callers have written anything
            # else in this session.
            await session.rollback()
            existing = await get_active_round(session)
            if existing is not None:
                logger.info("lost the race to open a round; using round %s", existing.id)
                return existing
            # Nothing active *and* the insert conflicted: the winner's transaction
            # hadn't committed yet when we looked. Try again rather than failing the
            # caller — a bet shouldn't 500 because of a scheduler tick's timing.
            logger.info("round-open conflict with nothing active yet (attempt %s), retrying", attempt + 1)
            continue
        # Published pre-commit (the caller commits right after) — acceptable: this
        # only tells subscribers "go refetch", and by the time an SSE client's
        # refetch request actually lands, this in-process commit (microseconds
        # away) has essentially always already happened.
        broadcaster.publish()
        return round_

    logger.error("could not open a round after %s attempts", _OPEN_ROUND_ATTEMPTS)
    return await get_active_round(session)