"""公共视图组件：async 分页 + 多租户基类 + 创建注入。

供 apps/catalog, apps/partner 等共享。
"""

from adrf.viewsets import ModelViewSet
from adrf.shortcuts import aget_object_or_404
from asgiref.sync import sync_to_async
from django.db.models import Q


def resolve_tenant(code):
    from apps.core.models import Tenant
    try:
        return Tenant.objects.get(code=code, is_active=True)
    except Tenant.DoesNotExist:
        return None


class StandardAsyncPagination:
    """手写 async 分页器（兼容 coroutine 或 queryset 入参）。"""

    page_size = 20
    page_size_query_param = "page_size"
    max_page_size = 200

    async def paginate_queryset(self, queryset, request, view=None):
        import asyncio

        if asyncio.iscoroutine(queryset):
            queryset = await queryset

        try:
            page_size = int(request.query_params.get(self.page_size_query_param, self.page_size))
        except (TypeError, ValueError):
            page_size = self.page_size
        if page_size < 1:                       # 0 / 负数会导致空切片或异常
            page_size = self.page_size
        page_size = min(page_size, self.max_page_size)

        try:
            page_number = int(request.query_params.get("page", 1))
        except (TypeError, ValueError):
            page_number = 1
        # 页码必须 ≥1：page=0/-1 会导致负索引切片（Django 会抛 ValueError → 500）
        if page_number < 1:
            page_number = 1

        self.total = await sync_to_async(queryset.count)()
        start = (page_number - 1) * page_size
        end = start + page_size
        sliced = await sync_to_async(lambda: list(queryset[start:end]))()
        return sliced

    def get_paginated_response(self, data):
        from rest_framework.response import Response
        return Response({
            "count": getattr(self, "total", 0),
            "next": None,
            "previous": None,
            "results": data,
        })


class BaseTenantViewSet(ModelViewSet):
    """通用：自动按租户过滤 + 软删除过滤 + 自定义 search + create 注入 tenant。"""

    pagination_class = StandardAsyncPagination

    async def get_tenant(self):
        tenant = getattr(self.request, "tenant_obj", None)
        if tenant is not None:
            return tenant
        from django.conf import settings

        code = self.request.META.get(
            "HTTP_X_TENANT_ID", settings.TENANT_DEFAULT
        )
        return await sync_to_async(resolve_tenant)(code)

    # 子类可声明关联预取，避免列表接口 N+1
    # （实测：未声明时 50 张销售单产生 311 条 SQL，声明后降到 3 条）
    select_related_fields: tuple = ()
    prefetch_related_fields: tuple = ()

    async def get_queryset(self):
        tenant = await self.get_tenant()
        if tenant is None:
            return self.model.objects.none()
        qs = self.model.objects.active().filter(tenant=tenant)

        # 关联预取：消除列表页 N+1（嵌套的 prefetch 用 "__" 路径）
        if self.select_related_fields:
            qs = qs.select_related(*self.select_related_fields)
        if self.prefetch_related_fields:
            qs = qs.prefetch_related(*self.prefetch_related_fields)

        search = self.request.query_params.get("search", "").strip()
        if search and getattr(self, "search_fields", None):
            q = Q()
            for f in self.search_fields:
                q |= Q(**{f"{f}__icontains": search})
            qs = qs.filter(q)
        return qs

    async def aget_object(self):
        """修复 adrf aget_object 不支持 async get_queryset 的问题。

        adrf 原实现同步调用 self.get_queryset()，拿到 coroutine 后在
        aget_object_or_404 里 TypeError → 被吞成 Http404，导致全项目
        所有 detail 路由（retrieve/PUT/PATCH/DELETE）404。
        """
        queryset = await self.get_queryset()
        queryset = await self.afilter_queryset(queryset)
        lookup_url_kwarg = self.lookup_url_kwarg or self.lookup_field
        filter_kwargs = {self.lookup_field: self.kwargs[lookup_url_kwarg]}
        obj = await aget_object_or_404(queryset, **filter_kwargs)
        await sync_to_async(self.check_object_permissions)(self.request, obj)
        return obj

    async def acreate(self, request, *args, **kwargs):
        from rest_framework.exceptions import ValidationError
        from rest_framework import status
        from rest_framework.response import Response

        tenant = await self.get_tenant()
        if tenant is None:
            raise ValidationError({"tenant": "无法识别租户"})

        # 套餐配额拦截（批次 C1）：声明了 quota_kind 的 ViewSet 在写入前校验
        quota_kind = getattr(self, "quota_kind", None)
        if quota_kind:
            from apps.billing import quota as billing_quota

            def _check():
                return billing_quota.check_and_count(tenant, quota_kind, delta=1)

            try:
                await sync_to_async(_check)()
            except billing_quota.QuotaExceeded as exc:
                return Response(exc.as_dict(), status=status.HTTP_403_FORBIDDEN)

        serializer = self.get_serializer(data=request.data)
        serializer.is_valid(raise_exception=True)
        validated = serializer.validated_data
        validated["tenant"] = tenant
        if request.user.is_authenticated:
            validated["created_by"] = request.user
            validated["updated_by"] = request.user

        await sync_to_async(serializer.save)()
        return Response(serializer.data, status=status.HTTP_201_CREATED)