"""查询效率测试（迭代第 4 轮）。

**为什么需要**：单测只验证"结果对不对"，不验证"代价多大"。
实测发现列表接口的 N+1：50 张销售单产生 **311 条 SQL**、P95 266ms；
加预取后降到 **5 条 SQL**、P95 50ms（5.3 倍）。

本模块用 `assertNumQueries` 把"查询次数"钉死，防止后续改动悄悄退回 N+1。
"""

import pytest
from decimal import Decimal
from model_bakery import baker
from rest_framework.test import APIClient
from rest_framework_simplejwt.tokens import RefreshToken

from apps.catalog.models import Product, Unit
from apps.inventory.models import Stock, Warehouse
from apps.partner.models import Customer
from apps.sales import services as sales_services


class query_counter:
    """统计代码块内执行的 SQL 数量（替代未安装的 pytest-django helper）。"""

    def __init__(self):
        from django.db import connection
        from django.test.utils import CaptureQueriesContext

        self._ctx = CaptureQueriesContext(connection)

    def __enter__(self):
        self._ctx.__enter__()
        return self

    def __exit__(self, *args):
        return self._ctx.__exit__(*args)

    @property
    def count(self):
        return len(self._ctx.captured_queries)


@pytest.fixture
def auth_client(db, user, tenant):
    c = APIClient()
    refresh = RefreshToken.for_user(user)
    c.credentials(
        HTTP_AUTHORIZATION=f"Bearer {refresh.access_token}",
        HTTP_X_TENANT_ID=tenant.code,
    )
    return c


@pytest.fixture
def warehouse(db, tenant):
    return baker.make(Warehouse, tenant=tenant, code="WH01", name="主仓")


@pytest.fixture
def customer(db, tenant):
    return baker.make(Customer, tenant=tenant, code="C001", name="张三",
                      credit_limit=Decimal("999999"))


@pytest.fixture
def product(db, tenant):
    unit = baker.make(Unit, tenant=tenant, code="bottle", name="瓶", is_base=True)
    return baker.make(Product, tenant=tenant, code="P001", name="可乐",
                      sale_price=Decimal("10"), base_unit=unit)


def _seed_bills(tenant, warehouse, customer, product, n=20):
    from apps.inventory import services as inv

    inv.inbound(tenant=tenant, warehouse=warehouse, product=product,
                quantity=Decimal(str(n * 10)), unit_cost=Decimal("5"))
    for _ in range(n):
        sales_services.create_sales_bill(
            tenant=tenant, customer=customer, warehouse=warehouse,
            lines=[{"product": product, "quantity": 2, "unit_price": 10}],
        )


# ============================================================
# 销售单列表：查询次数不随单据数增长
# ============================================================


def test_sales_bill_list_query_count_is_constant(db, auth_client, tenant,
                                                 warehouse, customer, product):
    """20 张单的列表页：SQL 次数必须是常数级（不随行数增长）。

    修复前：每张单 6 条（aggregate 税额 + lines + product + source_unit）= 120+ 条。
    修复后：预取 + 内存汇总 = 常数条。
    """
    _seed_bills(tenant, warehouse, customer, product, n=20)

    with query_counter() as qc:
        resp = auth_client.get("/api/v1/sales/bills/?page_size=50")
    assert resp.status_code == 200
    assert resp.json()["count"] == 20
    # 20 张单的查询数必须是常数级（修复前 120+）
    assert qc.count <= 12, f"查询数过多（疑似 N+1）：{qc.count} 条 SQL"


def test_sales_bill_list_scales_flat(db, auth_client, tenant, warehouse,
                                     customer, product):
    """单据翻倍（20 → 40）时查询次数不增加。"""
    from django.test.utils import CaptureQueriesContext
    from django.db import connection

    _seed_bills(tenant, warehouse, customer, product, n=20)
    with CaptureQueriesContext(connection) as ctx20:
        auth_client.get("/api/v1/sales/bills/?page_size=50")
    n20 = len(ctx20.captured_queries)

    _seed_bills(tenant, warehouse, customer, product, n=20)   # 再来 20 张
    with CaptureQueriesContext(connection) as ctx40:
        resp = auth_client.get("/api/v1/sales/bills/?page_size=50")
    n40 = len(ctx40.captured_queries)

    assert resp.json()["count"] == 40
    # 40 张单的查询数不应显著多于 20 张（允许 ±2 的波动）
    assert n40 <= n20 + 2, f"查询数随数据量增长：{n20} → {n40}（N+1 回归）"


def test_sales_bill_list_payload_correct(db, auth_client, tenant, warehouse,
                                         customer, product):
    """优化后数据必须仍然正确（预取不能丢字段）。"""
    _seed_bills(tenant, warehouse, customer, product, n=3)

    body = auth_client.get("/api/v1/sales/bills/?page_size=50").json()
    assert body["count"] == 3
    row = body["results"][0]
    # 预取后仍要能拿到客户名、行明细、税额合计
    assert row["customer_name"] == "张三"
    assert row["lines"], "行明细丢失"
    assert "tax_total" in row
    assert row["lines"][0]["product_name"] == "可乐"
    assert row["lines"][0]["unit_name"] == "瓶"


# ============================================================
# 其他列表接口
# ============================================================


def test_stock_list_no_n_plus_1(db, auth_client, tenant, warehouse, product):
    from apps.inventory import services as inv

    for i in range(15):
        p = baker.make(Product, tenant=tenant, code=f"SP{i:03d}", name=f"库存品{i}",
                       sale_price=Decimal("5"))
        inv.inbound(tenant=tenant, warehouse=warehouse, product=p,
                    quantity=Decimal("10"), unit_cost=Decimal("1"))

    with query_counter() as qc:
        resp = auth_client.get("/api/v1/inventory/stocks/?page_size=50")
    assert resp.status_code == 200
    assert resp.json()["count"] == 15
    assert qc.count <= 10, f"库存列表 N+1：{qc.count} 条 SQL"


def test_product_list_no_n_plus_1(db, auth_client, tenant):
    for i in range(20):
        baker.make(Product, tenant=tenant, code=f"PP{i:03d}", name=f"商品{i}",
                   sale_price=Decimal("5"))

    with query_counter() as qc:
        resp = auth_client.get("/api/v1/catalog/products/?page_size=50")
    assert resp.status_code == 200
    assert resp.json()["count"] == 20
    assert qc.count <= 10, f"商品列表 N+1：{qc.count} 条 SQL"


def test_receivable_list_no_n_plus_1(db, auth_client, tenant):
    from apps.finance.models import Receivable

    c = baker.make(Customer, tenant=tenant, code="CN1", name="客户1")
    for i in range(15):
        baker.make(Receivable, tenant=tenant, customer=c, bill_no=f"RC{i:03d}",
                   total_amount=Decimal("100"), status="open")

    with query_counter() as qc:
        resp = auth_client.get("/api/v1/finance/receivables/?page_size=50")
    assert resp.status_code == 200
    assert resp.json()["count"] == 15
    # 客户名要能取到（说明 select_related 生效）
    assert resp.json()["results"][0]["customer_name"] == "客户1"
    assert qc.count <= 10, f"应收列表 N+1：{qc.count} 条 SQL"


# ============================================================
# 分页边界：page_size 上限保护
# ============================================================


def test_page_size_capped_at_max(db, auth_client, tenant):
    """page_size 有上限，防止一次拉全表拖垮服务。"""
    for i in range(30):
        baker.make(Product, tenant=tenant, code=f"CAP{i:03d}", name=f"上限品{i}")

    resp = auth_client.get("/api/v1/catalog/products/?page_size=100000")
    assert resp.status_code == 200
    assert len(resp.json()["results"]) <= 200      # max_page_size