Stardream
122 lines
4.2 KiB
Python
122 lines
4.2 KiB
Python
import random
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import uuid
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from datetime import datetime
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from sqlalchemy import select
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from sqlalchemy.ext.asyncio import AsyncSession
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from app.models.lottery import Lottery, LotteryStatus
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from app.models.participant import Participant
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from app.models.prize import Prize
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from app.models.user import User
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from app.models.winner import Winner
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async def execute_draw(db: AsyncSession, lottery_id: uuid.UUID, trigger: str = "manual") -> list[dict]:
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"""
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Draw winners by randomly pairing shuffled participants with shuffled prizes.
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Both lists are shuffled independently so prize order has no bearing on results.
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n_winners = min(participants, total prize slots).
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Uses SELECT FOR UPDATE to prevent concurrent draws from producing duplicate
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winner sets. The status is transitioned to DRAWING inside the lock before
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any reads, so a second concurrent request will fail the status check.
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"""
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# Lock the lottery row - serialises all concurrent draw requests
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lottery_result = await db.execute(
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select(Lottery).where(Lottery.id == lottery_id).with_for_update()
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)
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lottery = lottery_result.scalar_one()
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# Re-check status under lock; may have changed since the router pre-checked
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if lottery.status != LotteryStatus.ACTIVE:
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raise ValueError("Lottery is no longer active")
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# Mark as DRAWING immediately so any concurrent request sees the changed
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# status and aborts before we even touch participants/prizes
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lottery.status = LotteryStatus.DRAWING
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await db.flush()
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# Load participants with user info
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result = await db.execute(
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select(Participant, User)
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.join(User, Participant.user_id == User.id)
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.where(Participant.lottery_id == lottery_id)
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)
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rows = result.all()
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if not rows:
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# Roll back the DRAWING status so the lottery stays usable
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lottery.status = LotteryStatus.ACTIVE
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await db.commit()
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raise ValueError("No participants in this lottery")
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# Load prizes
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prize_result = await db.execute(
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select(Prize).where(Prize.lottery_id == lottery_id)
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)
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prizes = prize_result.scalars().all()
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if not prizes:
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lottery.status = LotteryStatus.ACTIVE
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await db.commit()
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raise ValueError("No prizes configured")
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# Expand prizes by quantity: Prize(qty=3) → [Prize, Prize, Prize]
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expanded_prizes: list[Prize] = []
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for prize in prizes:
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expanded_prizes.extend([prize] * prize.quantity)
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random.shuffle(expanded_prizes)
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now = datetime.utcnow()
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winners_data = []
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if lottery.allow_multiple_wins:
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# Draw with replacement: all prize slots awarded, same participant can win multiple
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for prize in expanded_prizes:
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participant, user = random.choice(rows)
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db.add(Winner(
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lottery_id=lottery_id,
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user_id=user.id,
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prize_id=prize.id,
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prize_name=prize.name,
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drawn_at=now,
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))
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winners_data.append({
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"user_id": user.id,
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"username": user.username,
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"first_name": user.first_name,
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"last_name": user.last_name,
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"prize_name": prize.name,
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"drawn_at": now,
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})
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else:
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# No repeat wins: shuffle participants and pair 1-to-1 with prizes
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random.shuffle(rows)
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n_winners = min(len(rows), len(expanded_prizes))
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for i in range(n_winners):
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participant, user = rows[i]
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prize = expanded_prizes[i]
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db.add(Winner(
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lottery_id=lottery_id,
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user_id=user.id,
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prize_id=prize.id,
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prize_name=prize.name,
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drawn_at=now,
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))
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winners_data.append({
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"user_id": user.id,
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"username": user.username,
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"first_name": user.first_name,
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"last_name": user.last_name,
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"prize_name": prize.name,
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"drawn_at": now,
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})
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lottery.status = LotteryStatus.FINISHED
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lottery.drawn_at = now
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lottery.draw_trigger = trigger
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await db.commit()
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return winners_data
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