"""sales 序列化器（async 兼容）。"""

from rest_framework import serializers
from apps.core.serializers import AsyncModelSerializer
from .models import SalesOrder, SalesOrderLine, SalesBill, SalesBillLine


class SalesOrderLineSerializer(AsyncModelSerializer):
    product_code = serializers.CharField(source="product.code", read_only=True)
    product_name = serializers.CharField(source="product.name", read_only=True)

    class Meta:
        model = SalesOrderLine
        fields = ["id", "product", "product_code", "product_name",
                  "quantity", "unit_price", "amount", "delivered_qty"]
        read_only_fields = ["id", "amount", "delivered_qty"]


class SalesOrderSerializer(AsyncModelSerializer):
    customer_code = serializers.CharField(source="customer.code", read_only=True)
    warehouse_code = serializers.CharField(source="warehouse.code", read_only=True)
    lines = SalesOrderLineSerializer(many=True, required=False)

    class Meta:
        model = SalesOrder
        fields = [
            "id", "bill_no", "customer", "customer_code",
            "warehouse", "warehouse_code",
            "bill_date", "expected_date", "total_amount", "state", "remark",
            "lines",
        ]
        read_only_fields = ["id", "bill_no", "total_amount", "state"]


class SalesBillLineSerializer(AsyncModelSerializer):
    product_code = serializers.CharField(source="product.code", read_only=True)
    product_name = serializers.CharField(source="product.name", read_only=True)
    unit_name = serializers.SerializerMethodField()

    class Meta:
        model = SalesBillLine
        fields = ["id", "product", "product_code", "product_name",
                  "quantity", "source_unit", "source_quantity", "unit_name",
                  "unit_price", "amount", "tax_rate", "tax_amount"]
        read_only_fields = ["id", "amount", "tax_amount"]

    def get_unit_name(self, obj):
        unit = obj.source_unit or getattr(obj.product, "base_unit", None)
        return unit.name if unit else ""


class SalesBillSerializer(AsyncModelSerializer):
    customer_code = serializers.CharField(source="customer.code", read_only=True)
    customer_name = serializers.CharField(source="customer.name", read_only=True)
    warehouse_code = serializers.CharField(source="warehouse.code", read_only=True)
    round_off = serializers.DecimalField(max_digits=18, decimal_places=4, read_only=True)
    # 单据税额合计 = 各行 tax_amount 之和（D4；前端展示"其中税额"）
    tax_total = serializers.SerializerMethodField()
    lines = SalesBillLineSerializer(many=True, required=False)

    def get_tax_total(self, obj):
        """在内存里汇总已预取的行，避免每张单一次 aggregate（N+1）。

        旧实现 `obj.lines.aggregate(Sum("tax_amount"))` 对列表页的每一行都发一条 SQL
        （实测 50 张单 = 50 次聚合）。列表接口已 prefetch `lines`，
        这里直接遍历内存对象即可。详情接口若未预取，all() 也只多一次查询。
        """
        return str(sum((ln.tax_amount or 0) for ln in obj.lines.all()))

    class Meta:
        model = SalesBill
        fields = [
            "id", "bill_no", "customer", "customer_code", "customer_name",
            "warehouse", "warehouse_code", "order",
            "bill_date", "total_amount", "round_off", "tax_total", "state", "remark",
            "lines",
        ]
        read_only_fields = ["id", "bill_no", "total_amount", "state"]