GO处理一些未知结构的JSON，纠结一个星期了

这是elasticsearch的返回结构，aggregations中的user、tags、ct等都是不可预知的字段，要如何取出这些结构，并还原成一维map？

{
    "took": 2,
    "timed_out": false,
    "_shards": {
        "total": 5,
        "successful": 3,
        "failed": 0
    },
    "hits": {
        "total": 22,
        "max_score": 0,
        "hits": []
    },
    "aggregations": {
        "user": {
            "doc_count_error_upper_bound": 0,
            "sum_other_doc_count": 0,
            "buckets": [
                {
                    "key": "olivere",
                    "doc_count": 16,
                    "tags": {
                        "doc_count_error_upper_bound": 0,
                        "sum_other_doc_count": 0,
                        "buckets": [
                            {
                                "key": "golang",
                                "doc_count": 16,
                                "ct": {
                                    "value": 16
                                }
                            },
                            {
                                "key": "elasticsearch",
                                "doc_count": 7,
                                "ct": {
                                    "value": 7
                                }
                            }
                        ]
                    }
                },
                {
                    "key": "sandrae",
                    "doc_count": 6,
                    "tags": {
                        "doc_count_error_upper_bound": 0,
                        "sum_other_doc_count": 0,
                        "buckets": [
                            {
                                "key": "cycling",
                                "doc_count": 6,
                                "ct": {
                                    "value": 6
                                }
                            },
                            {
                                "key": "sports",
                                "doc_count": 6,
                                "ct": {
                                    "value": 6
                                }
                            }
                        ]
                    }
                }
            ]
        }
    }
}