from rest_framework.generics import ListAPIView
from rest_framework.pagination import LimitOffsetPagination
from rest_framework import filters, serializers
from django_filters.rest_framework import DjangoFilterBackend
from django_filters import rest_framework as django_filters
from stock import models


class StockSnapshotSerializer(serializers.ModelSerializer):
    """库存快照序列化器"""
    product_name = serializers.CharField(source='product.name', read_only=True)
    product_code = serializers.CharField(source='product.code', read_only=True)
    warehouse_name = serializers.CharField(source='warehouse.name', read_only=True)
    unit_display = serializers.CharField(source='get_unit_display', read_only=True)
    stock_change_record_type = serializers.CharField(
        source='stock_change_record.get_type_display', 
        read_only=True
    )
    stock_change_record_source = serializers.CharField(
        source='stock_change_record.get_source_type_display', 
        read_only=True
    )
    
    class Meta:
        model = models.StockSnapshot
        fields = [
            'id', 'product', 'product_name', 'product_code',
            'warehouse', 'warehouse_name',
            'delta', 'quantity_before', 'quantity_after',
            'stock_change_record', 'stock_change_record_type', 'stock_change_record_source',
            'unit', 'unit_display', 'num_of_rolls',
            'offset_to', 'offset_at', 'cancelled', 'cancelled_at', 'offset_id',
            'created_at', 'updated_at'
        ]


class StockSnapshotFilterSet(django_filters.FilterSet):
    """库存快照过滤器"""
    product_name = django_filters.CharFilter(field_name='product__name', lookup_expr='icontains')
    product_code = django_filters.CharFilter(field_name='product__code', lookup_expr='icontains')
    warehouse_name = django_filters.CharFilter(field_name='warehouse__name', lookup_expr='icontains')
    cancelled = django_filters.BooleanFilter()
    has_offset = django_filters.BooleanFilter(method='filter_has_offset')
    date_from = django_filters.DateFilter(field_name='created_at', lookup_expr='gte')
    date_to = django_filters.DateFilter(field_name='created_at', lookup_expr='lte')
    
    def filter_has_offset(self, queryset, name, value):
        """过滤是否有冲抵记录"""
        if value:
            return queryset.exclude(offset_to__isnull=True)
        else:
            return queryset.filter(offset_to__isnull=True)
    
    class Meta:
        model = models.StockSnapshot
        fields = [
            'product', 'warehouse', 'stock_change_record',
            'unit', 'cancelled'
        ]


class StockSnapshotListView(ListAPIView):
    """
    库存快照列表视图（只读）
    
    提供库存变动快照的查询功能
    
    查询参数:
    - product: 产品ID
    - product_name: 产品名称（模糊查询）
    - product_code: 产品编码（模糊查询）
    - warehouse: 仓库ID
    - warehouse_name: 仓库名称（模糊查询）
    - stock_change_record: 关联的库存变动记录ID
    - unit: 单位
    - cancelled: 是否已取消（true/false）
    - has_offset: 是否有冲抵记录（true/false）
    - date_from: 开始日期（格式：YYYY-MM-DD）
    - date_to: 结束日期（格式：YYYY-MM-DD）
    - search: 全文搜索（产品名称、产品编码、仓库名称）
    - ordering: 排序字段
    """
    serializer_class = StockSnapshotSerializer
    pagination_class = LimitOffsetPagination
    filter_backends = [DjangoFilterBackend, filters.SearchFilter, filters.OrderingFilter]
    filterset_class = StockSnapshotFilterSet
    search_fields = ['product__name', 'product__code', 'warehouse__name']
    ordering_fields = [
        'id', 'delta', 'quantity_before', 'quantity_after',
        'created_at', 'updated_at', 'offset_at', 'cancelled_at'
    ]
    ordering = ['-created_at']
    
    def get_queryset(self):
        """优化查询，预加载关联数据"""
        return models.StockSnapshot.objects.select_related(
            'product', 'warehouse', 'stock_change_record'
        ).all()