"""用户店铺绑定：一人只能绑定一家店（业务约定）。"""
from django.db import transaction
from django.db.models import F

from shop.models import Dianpu, YonghuDianpuBangding

import logging

logger = logging.getLogger(__name__)


def get_latest_binding_qs(yonghu):
    """同一用户可能历史残留多条绑定，一律取最近更新的一条。"""
    return (
        YonghuDianpuBangding.objects
        .filter(yonghu=yonghu)
        .select_related('dianpu')
        .order_by('-UpdateTime', '-id')
    )


def get_user_shop_binding(yonghu):
    """读取当前生效绑定（最新一条）。"""
    return get_latest_binding_qs(yonghu).first()


def _delete_extra_bindings(yonghu, keep_id=None):
    """
    删除同一用户多余绑定行，并扣减对应店铺绑定数。
    keep_id: 保留的绑定主键；None 表示全部删除。
    """
    qs = YonghuDianpuBangding.objects.select_for_update().filter(yonghu=yonghu)
    if keep_id is not None:
        qs = qs.exclude(pk=keep_id)
    extras = list(qs.select_related('dianpu'))
    for row in extras:
        try:
            dianpu = row.dianpu
            dianpu.bangding_yonghushu = F('bangding_yonghushu') - 1
            dianpu.save(update_fields=['bangding_yonghushu'])
        except Exception:
            logger.warning('扣减多余绑定店铺人数失败 binding=%s', row.pk, exc_info=True)
        row.delete()
    return len(extras)


@transaction.atomic
def set_user_shop_binding(yonghu, dianpu):
    """
    将用户唯一绑定到 dianpu；清理多余行。
    返回 (changed: bool, msg: str)
    """
    yonghu_locked = type(yonghu).objects.select_for_update().get(pk=yonghu.pk)
    dianpu_locked = Dianpu.objects.select_for_update().get(pk=dianpu.pk)

    if dianpu_locked.zhuangtai != 1:
        return False, '店铺已被封禁，无法绑定'

    rows = list(
        YonghuDianpuBangding.objects.select_for_update()
        .filter(yonghu=yonghu_locked)
        .select_related('dianpu')
        .order_by('-UpdateTime', '-id')
    )

    if rows:
        primary = rows[0]
        if primary.dianpu_id == dianpu_locked.id:
            # 已是目标店：清掉多余行即可
            _delete_extra_bindings(yonghu_locked, keep_id=primary.pk)
            return False, '已绑定该店铺'

        old = primary.dianpu
        old.bangding_yonghushu = F('bangding_yonghushu') - 1
        old.save(update_fields=['bangding_yonghushu'])

        primary.dianpu = dianpu_locked
        primary.save(update_fields=['dianpu', 'UpdateTime'])
        _delete_extra_bindings(yonghu_locked, keep_id=primary.pk)
    else:
        primary = YonghuDianpuBangding.query.create(yonghu=yonghu_locked, dianpu=dianpu_locked)

    dianpu_locked.bangding_yonghushu = F('bangding_yonghushu') + 1
    dianpu_locked.save(update_fields=['bangding_yonghushu'])
    return True, '绑定成功'


@transaction.atomic
def clear_user_shop_binding(yonghu):
    """解除用户全部店铺绑定。返回被解除的主店铺 id 或 None。"""
    yonghu_locked = type(yonghu).objects.select_for_update().get(pk=yonghu.pk)
    primary = get_latest_binding_qs(yonghu_locked).first()
    old_id = primary.dianpu_id if primary else None
    _delete_extra_bindings(yonghu_locked, keep_id=None)
    return old_id