"""采购业务服务：确认订单 / 进货单过账（写库存 + 生成应付）。"""

from __future__ import annotations

from datetime import date
from decimal import Decimal

from django.db import transaction

from apps.inventory import services as inv_services
from apps.finance import services as fin_services
from apps.core.services import (
    compute_tax,
    parse_price,
    resolve_line_quantity,
    resolve_tax_rate,
)

from .models import PurchaseOrder, PurchaseOrderLine, PurchaseBill, PurchaseBillLine


def _resolve_line(product, ln):
    """解析采购行：换算基本单位数量 + 录入单位/数量；价格按录入单位。

    返回 (qty, price, src_unit, src_qty, amount, tax_rate, tax_amount)（D4 加税）。
    """
    parsed = resolve_line_quantity(product, ln)
    qty = parsed["quantity"]
    src_unit = parsed["source_unit"]
    src_qty = parsed["source_quantity"]
    # 单价校验（与销售侧同口径）：必须 > 0，否则拒绝
    # （此前直接 Decimal(str(...)) 未校验，0 价只能靠下游"金额>0"兜住，
    #   错误码不精确；0 成本入库还会污染加权平均成本）
    price = parse_price(product, ln.get("unit_price"))
    if src_unit is not None:
        from apps.catalog.models import UnitConversion
        conv = UnitConversion.objects.filter(product=product, unit=src_unit).first()
        rate = conv.rate if conv else None
        amount = src_qty * price
    else:
        rate = None
        amount = qty * price

    tax_rate = resolve_tax_rate(product, ln)
    tax = compute_tax(amount, tax_rate)
    return qty, price, src_unit, src_qty, amount, tax_rate, tax["tax"]


def _generate_bill_no(tenant, prefix: str) -> str:
    """取候选单号（唯一性由 create_with_unique_bill_no 的重试保证）。"""
    Model = PurchaseOrder if prefix == "PO" else PurchaseBill
    from apps.core.services import next_bill_no

    return next_bill_no(tenant, prefix, Model)


@transaction.atomic
def create_purchase_bill(
    *, tenant, supplier, warehouse, bill_date=None, remark="", lines=None,
    order=None,
) -> PurchaseBill:
    """新建一张进货单（草稿态）。lines: list of dict(product, quantity, unit_price)。"""
    bill_date = bill_date or date.today()
    from apps.core.services import create_with_unique_bill_no

    bill = create_with_unique_bill_no(
        PurchaseBill,
        tenant=tenant,
        prefix="PB",
        defaults=dict(
            supplier=supplier,
            warehouse=warehouse,
            order=order,
            bill_date=bill_date,
            total_amount=Decimal("0"),
            state="draft",
            remark=remark,
        ),
    )
    total = Decimal("0")
    for ln in lines or []:
        product = ln["product"]
        qty, price, src_unit, src_qty, amount, tax_rate, tax_amount = _resolve_line(product, ln)
        PurchaseBillLine.objects.create(
            tenant=tenant,
            bill=bill,
            product=product,
            quantity=qty,
            unit_price=price,
            amount=amount,
            batch_no=str(ln.get("batch_no") or ""),
            production_date=ln.get("production_date"),
            expiry_date=ln.get("expiry_date"),
            source_unit=src_unit,
            source_quantity=src_qty,
            tax_rate=tax_rate,
            tax_amount=tax_amount,
        )
        total += amount
    if total <= 0:
        raise ValueError(f"进货单金额必须大于 0（行合计 {total}）；请检查数量与单价")

    bill.total_amount = total
    bill.save(update_fields=["total_amount", "updated_at"])
    return bill


@transaction.atomic
def confirm_purchase_bill(bill: PurchaseBill, *, user=None) -> PurchaseBill:
    """进货单过账：写库存 + 生成应付单。

    必须状态是 draft；过账后变 confirmed。
    """
    if bill.state != "draft":
        raise ValueError(f"purchase bill {bill.bill_no} not in draft state")
    # 1. 写库存
    for line in bill.lines.select_related("product").all():
        inv_services.inbound(
            tenant=bill.tenant,
            warehouse=bill.warehouse,
            product=line.product,
            quantity=line.quantity,
            unit_cost=line.unit_price,
            source_type="purchase",
            source_ref=bill.bill_no,
            batch_no=line.batch_no,
            production_date=line.production_date,
            expiry_date=line.expiry_date,
        )
    # 2. 生成应付（D4：把行税额合计传给凭证做进项税拆分）
    from django.db.models import Sum as _Sum

    tax_total = bill.lines.aggregate(t=_Sum("tax_amount"))["t"] or Decimal("0")
    fin_services.create_payable_from_purchase(
        tenant=bill.tenant,
        supplier=bill.supplier,
        total_amount=bill.total_amount,
        source_ref=bill.bill_no,
        bill_date=bill.bill_date,
        tax_amount=tax_total,
    )
    # 3. 改状态
    bill.state = "confirmed"
    bill.save(update_fields=["state", "updated_at"])

    from apps.core import audit as audit_log

    audit_log.log_bill_posted(
        tenant=bill.tenant, bill=bill, user=user,
        extra={"lines": bill.lines.count()},
    )
    return bill