"""统一业务异常与错误响应体（需求 §37 → 统一 code+message+detail）。

对外格式：{"code": "...", "message": "中文文案", "detail": null}
未捕获异常兜底为 500 INTERNAL_ERROR，原始异常只进日志。
"""

from typing import Any

from fastapi import Request, status
from fastapi.exceptions import RequestValidationError
from fastapi.responses import JSONResponse
from starlette.exceptions import HTTPException as StarletteHTTPException

from app.core.logging import get_logger

logger = get_logger(__name__)


class AppError(Exception):
    """业务异常基类。"""

    status_code: int = status.HTTP_500_INTERNAL_SERVER_ERROR
    code: str = "INTERNAL_ERROR"
    message: str = "服务内部错误，请稍后重试。"

    def __init__(
        self,
        message: str | None = None,
        *,
        detail: Any = None,
        code: str | None = None,
    ) -> None:
        self.detail = detail
        if message is not None:
            self.message = message
        if code is not None:
            self.code = code
        super().__init__(self.message)

    def to_response(self) -> JSONResponse:
        return JSONResponse(
            status_code=self.status_code,
            content={"code": self.code, "message": self.message, "detail": self.detail},
        )


# --- 通用 ---


class NotFoundError(AppError):
    status_code = status.HTTP_404_NOT_FOUND
    code = "NOT_FOUND"
    message = "资源不存在。"


class PermissionDeniedError(AppError):
    status_code = status.HTTP_403_FORBIDDEN
    code = "PERMISSION_DENIED"
    message = "没有权限访问该资源。"


class AuthRequiredError(AppError):
    status_code = status.HTTP_401_UNAUTHORIZED
    code = "AUTH_REQUIRED"
    message = "请先登录。"


class InvalidCredentialsError(AppError):
    status_code = status.HTTP_401_UNAUTHORIZED
    code = "AUTH_INVALID_CREDENTIALS"
    message = "用户名或密码错误。"


class ConflictError(AppError):
    status_code = status.HTTP_409_CONFLICT
    code = "CONFLICT"
    message = "资源冲突。"


class RateLimitedError(AppError):
    status_code = status.HTTP_429_TOO_MANY_REQUESTS
    code = "RATE_LIMITED"
    message = "请求过于频繁，请稍后再试。"


class LinkExpiredError(AppError):
    """AI 链接已过期（HTTP 410 Gone）。"""
    status_code = status.HTTP_410_GONE
    code = "LINK_EXPIRED"
    message = "链接已失效，请重新生成。"


# --- 上传与配额 ---


class StorageQuotaExceededError(AppError):
    status_code = status.HTTP_413_CONTENT_TOO_LARGE
    code = "STORAGE_QUOTA_EXCEEDED"
    message = "存储空间不足。"


class FileTooLargeError(AppError):
    status_code = status.HTTP_413_CONTENT_TOO_LARGE
    code = "FILE_TOO_LARGE"
    message = "单个文件大小超出限制。"


class FileTypeUnsupportedError(AppError):
    status_code = status.HTTP_415_UNSUPPORTED_MEDIA_TYPE
    code = "FILE_TYPE_UNSUPPORTED"
    message = "不支持的文件类型。"


# --- 异常处理器 ---


async def app_error_handler(_: Request, exc: AppError) -> JSONResponse:
    if exc.status_code >= 500:
        logger.error("AppError %s: %s", exc.code, exc.message, exc_info=exc)
    return exc.to_response()


async def validation_error_handler(_: Request, exc: RequestValidationError) -> JSONResponse:
    # 序列化错误详情，过滤不可 JSON 序列化的对象
    errors = []
    for err in exc.errors():
        clean_err = {
            "type": err.get("type", ""),
            "loc": err.get("loc", []),
            "msg": err.get("msg", ""),
        }
        if "input" in err:
            clean_err["input"] = str(err["input"])
        errors.append(clean_err)

    return JSONResponse(
        status_code=status.HTTP_422_UNPROCESSABLE_ENTITY,
        content={
            "code": "VALIDATION_ERROR",
            "message": "请求参数不正确。",
            "detail": errors,
        },
    )


_STATUS_CODE_MAP = {
    status.HTTP_404_NOT_FOUND: ("NOT_FOUND", "资源不存在。"),
    status.HTTP_405_METHOD_NOT_ALLOWED: ("METHOD_NOT_ALLOWED", "请求方法不被允许。"),
    status.HTTP_401_UNAUTHORIZED: ("AUTH_REQUIRED", "请先登录。"),
}


async def http_exception_handler(_: Request, exc: StarletteHTTPException) -> JSONResponse:
    """把框架层 HTTPException（如未匹配路由的 404）转成统一错误体。"""
    code, message = _STATUS_CODE_MAP.get(exc.status_code, ("HTTP_ERROR", str(exc.detail)))
    return JSONResponse(
        status_code=exc.status_code,
        content={"code": code, "message": message, "detail": None},
    )


async def unhandled_error_handler(request: Request, exc: Exception) -> JSONResponse:
    logger.error("Unhandled: %s %s", request.method, request.url.path, exc_info=exc)
    return JSONResponse(
        status_code=status.HTTP_500_INTERNAL_SERVER_ERROR,
        content={"code": "INTERNAL_ERROR", "message": "服务内部错误，请稍后重试。", "detail": None},
    )


def register_exception_handlers(app: Any) -> None:
    app.add_exception_handler(AppError, app_error_handler)
    app.add_exception_handler(RequestValidationError, validation_error_handler)
    app.add_exception_handler(StarletteHTTPException, http_exception_handler)
    app.add_exception_handler(Exception, unhandled_error_handler)