"""积分钱包服务：统一余额变更入口（行锁 + 流水 + 乐观锁，对齐《02-技术文档》3.4）"""
from sqlalchemy import select
from sqlalchemy.ext.asyncio import AsyncSession

from app.core import errors
from app.core.response import BizException
from app.models.billing import PointTransaction
from app.models.user import UserWallet

# 流水业务类型
BIZ_RECHARGE = 1      # 充值
BIZ_WATCH = 2         # 观看消耗
BIZ_COMMENT = 3       # 评论奖励
BIZ_MEMBERSHIP = 4    # 开通会员
BIZ_GIFT = 5          # 活动赠送
BIZ_ADJUST = 6        # 后台调整
BIZ_CLAWBACK = 7      # 奖励扣回/退款扣回
BIZ_REFERRAL = 8      # 推荐奖励


async def get_or_create_wallet(db: AsyncSession, user_id: int, for_update: bool = False) -> UserWallet:
    stmt = select(UserWallet).where(UserWallet.user_id == user_id)
    if for_update:
        stmt = stmt.with_for_update()
    wallet = (await db.execute(stmt)).scalar_one_or_none()
    if wallet is None:
        wallet = UserWallet(user_id=user_id)
        db.add(wallet)
        await db.flush()
        if for_update:
            # 新建后再加行锁，保证后续并发读到同一行
            wallet = (await db.execute(stmt)).scalar_one()
    return wallet


async def change_points(
    db: AsyncSession,
    user_id: int,
    amount: int,
    biz_type: int,
    biz_id: str = "",
    remark: str = "",
    allow_negative: bool = False,
) -> int:
    """变更积分余额，返回变动后余额。

    - amount 正增负减；扣减默认不允许透支（退款扣回场景传 allow_negative=True，余额可为负）
    - 同事务内：行锁 → 校验/更新余额与累计 → 写流水
    """
    wallet = await get_or_create_wallet(db, user_id, for_update=True)
    new_balance = wallet.points + amount
    if amount < 0 and new_balance < 0 and not allow_negative:
        raise BizException(errors.POINTS_NOT_ENOUGH)

    wallet.points = new_balance
    wallet.version += 1
    if amount > 0:
        if biz_type == BIZ_RECHARGE:
            wallet.total_recharge += amount
        else:
            wallet.total_earned += amount
    else:
        wallet.total_consumed += -amount

    db.add(
        PointTransaction(
            user_id=user_id,
            change_amount=amount,
            balance_after=new_balance,
            biz_type=biz_type,
            biz_id=biz_id,
            remark=remark,
        )
    )
    await db.flush()
    return new_balance


async def get_balance(db: AsyncSession, user_id: int) -> int:
    wallet = await get_or_create_wallet(db, user_id)
    return wallet.points