# 续写同一文件：reading_project/src/library/views.py
def book_form(request, book=None):
    # POST 即使为空也要绑定，让 required 字段给出错误。
    form = BookForm(
        request.POST if request.method == "POST" else None,
        instance=book,
        user=request.user,
    )
    status = 200
    if request.method == "POST":
        status = 422
        if form.is_valid():
            try:
                saved = save_book(form, request.user)
            except IntegrityError as exc:
                if (
                    getattr(exc.__cause__, "sqlite_errorname", "")
                    != "SQLITE_CONSTRAINT_UNIQUE"
                ):
                    raise
                # 在 atomic 外处理异常；本次事务已经回滚。
                form.add_error(None, "保存时发生同名冲突，请修改后重试")
                status = 409
            else:
                messages.success(request, "已保存阅读记录")
                return redirect("library:detail", pk=saved.pk)
    return render(
        request, "library/book_form.html", {"form": form, "book": book}, status=status
    )


@login_required
def create(request):
    return book_form(request)


@login_required
def edit(request, pk):
    return book_form(request, owned_book(request.user, pk))


@login_required
@require_POST
def delete(request, pk):
    with transaction.atomic():
        owned_book(request.user, pk).delete()
    messages.success(request, "已删除书籍")
    return redirect("library:index")