"""统一业务异常 → HTTP 语义映射（迭代第 2 轮）。

**为什么需要**：迭代第 1 轮发现 `InvalidLineQuantity` / `BelowMinPrice` /
`CreditLimitExceeded` 等业务异常要在每个视图里手写 try/except——漏一处就是 500。
本模块把它们收敛到一处映射，视图只写业务逻辑。

映射表（HTTP 语义 + `code` 供前端判别）：

| 异常 | HTTP | code |
|---|---|---|
| InvalidLineQuantity / InvalidLinePrice | 400 | invalid_quantity / invalid_price |
| BelowMinPrice | 400 | below_min_price |
| InsufficientStock | 400 | insufficient_stock |
| StorefrontError（各类） | 400/402/403 | 见下方细分 |
| QuotaExceeded（billing / ai） | 403 | quota_exceeded |
| CreditLimitExceeded | 402 | credit_limit_exceeded |
| DrawingStateError / ValueError（业务） | 400 | invalid_state |
| Unhandled Exception | 500 | server_error（含日志） |
"""

from __future__ import annotations

import logging

from rest_framework import status
from rest_framework.response import Response
from rest_framework.views import exception_handler as drf_exception_handler

logger = logging.getLogger("dealerhub.api")


def api_exception_handler(exc, context):
    """DRF 全局异常处理器：业务异常 → 结构化 JSON。

    返回值约定：与 DRF 一致（Response 或 None）；None 表示交给 Django 处理。
    """
    # 1. 业务异常：显式映射（这些是"可预期"的错误，用 4xx + code 表达）
    mapped = _map_business_exception(exc)
    if mapped is not None:
        return mapped

    # 2. 其他异常交给 DRF（ValidationError / NotFound / PermissionDenied 等）
    response = drf_exception_handler(exc, context)

    # 3. 兜底：未被处理的异常（DRF 也返回 None → Django 会 500）
    #    这里统一记日志并返回结构化 500，避免把栈信息暴露给客户端
    if response is None:
        view = context.get("view")
        logger.exception(
            "未处理异常 · view=%s · path=%s · exc=%s",
            view.__class__.__name__ if view else "?",
            context.get("request").path if context.get("request") else "?",
            type(exc).__name__,
        )
        return Response({
            "code": "server_error",
            "detail": "服务端处理异常，请稍后重试或联系管理员",
        }, status=status.HTTP_500_INTERNAL_SERVER_ERROR)

    return _with_error_code(response, exc)


def _with_error_code(response, exc):
    """给"单条 detail"型错误补一个顶层 `code`，供前端判别。

    DRF 把 code 藏在 ErrorDetail 里，序列化成纯字符串就丢了，所以
    PermissionDenied / NotAuthenticated / NotFound 这类响应到这里补回来。

    只处理 detail 为字符串的情况：ValidationError 的 dict 形态是字段级错误，
    顶层再塞一个 `code` 会和真实字段名（如 `{"code": ["已存在"]}`）撞车。
    """
    data = getattr(response, "data", None)
    if not isinstance(data, dict) or "code" in data:
        return response
    if not isinstance(getattr(exc, "detail", None), str):
        return response
    try:
        codes = exc.get_codes()
    except Exception:                                   # 非 DRF 异常
        return response
    if not isinstance(codes, str):
        return response
    data["code"] = codes
    return response


def _map_business_exception(exc):
    """把已知业务异常翻译成 Response；不认识则返回 None。"""
    # ---- 单据行校验（D4 / 迭代第 1 轮） ----
    from apps.core.services import (
        BelowMinPrice, InvalidLinePrice, InvalidLineQuantity,
    )

    if isinstance(exc, InvalidLineQuantity):
        return Response({
            "code": "invalid_quantity",
            "detail": str(exc),
            "product_code": exc.product_code,
            "reason": exc.reason,
        }, status=status.HTTP_400_BAD_REQUEST)

    if isinstance(exc, InvalidLinePrice):
        return Response({
            "code": "invalid_price",
            "detail": str(exc),
            "product_code": exc.product_code,
            "reason": exc.reason,
        }, status=status.HTTP_400_BAD_REQUEST)

    if isinstance(exc, BelowMinPrice):
        return Response({
            "code": "below_min_price",
            "detail": str(exc),
            "product_code": exc.product_code,
            "unit_price": str(exc.unit_price),
            "min_price": str(exc.min_price),
        }, status=status.HTTP_400_BAD_REQUEST)

    # ---- 库存 ----
    from apps.inventory.services import InsufficientStock

    if isinstance(exc, InsufficientStock):
        return Response({
            "code": "insufficient_stock",
            "detail": str(exc),
        }, status=status.HTTP_400_BAD_REQUEST)

    # ---- 信用额度（销售） ----
    from apps.sales.services import CreditLimitExceeded

    if isinstance(exc, CreditLimitExceeded):
        return Response({
            "code": "credit_limit_exceeded",
            "detail": (
                f"客户 {exc.customer_code} 信用超限：已用 {exc.outstanding} + "
                f"本单 {exc.extra} > 额度 {exc.limit}"
            ),
            "customer_code": exc.customer_code,
            "outstanding": str(exc.outstanding),
            "limit": str(exc.limit),
            "this_bill": str(exc.extra),
        }, status=status.HTTP_402_PAYMENT_REQUIRED)

    # ---- 套餐/配额（billing 与 ai 两处，ai 的继承自 billing） ----
    try:
        from apps.billing.quota import QuotaExceeded

        if isinstance(exc, QuotaExceeded):
            return Response(exc.as_dict(), status=status.HTTP_403_FORBIDDEN)
    except ImportError:
        pass

    try:
        from apps.ai.usage import QuotaExceeded as AiQuotaExceeded

        if isinstance(exc, AiQuotaExceeded):
            return Response(exc.as_dict(), status=status.HTTP_403_FORBIDDEN)
    except ImportError:
        pass

    # ---- 商城 ----
    try:
        from apps.storefront.services import (
            CreditLimitExceeded as SfCreditLimit,
            ProductNotAuthorized,
            StorefrontError,
        )

        if isinstance(exc, ProductNotAuthorized):
            return Response({
                "code": "product_not_authorized",
                "detail": str(exc),
            }, status=status.HTTP_403_FORBIDDEN)
        if isinstance(exc, SfCreditLimit):
            return Response({
                "code": "credit_limit_exceeded",
                "detail": str(exc),
            }, status=status.HTTP_402_PAYMENT_REQUIRED)
        if isinstance(exc, StorefrontError):
            return Response({
                "code": "invalid_order",
                "detail": str(exc),
            }, status=status.HTTP_400_BAD_REQUEST)
    except ImportError:
        pass

    return None