Elasticsearch use the key of term aggregation as the input in script - elasticsearch

Question

I stored the result of each game as a doc. The players and their scores were stored in users and scores arrays.
Sample data :
[
{
"gameId": "game01",
"users": [
"user01",
"user02"
],
"#timestamp": "2022-08-11T17:00:00.000Z",
"scores": [
4,
1
]
},
{
"gameId": "game02",
"users": [
"user01",
"user02"
],
"#timestamp": "2022-08-12T17:00:00.000Z",
"scores": [
3,
1
]
},
{
"gameId": "game02",
"users": [
"user02",
"user03"
],
"#timestamp": "2022-08-12T18:00:00.000Z",
"scores": [
2,
4
]
}
]
I expected to use the below query to aggregate the daily total scores of each game of users:
{
"aggs": {
"aggByDate": {
"date_histogram": {
"field": "#timestamp",
"interval": "1d",
"time_zone": "+8",
"min_doc_count": 1
},
"aggs": {
"aggByGame": {
"terms": {
"field": "gameId"
},
"aggs": {
"aggByUser": {
"terms": {
"field": "users"
},
"aggs": {
"totalScore": {
"sum": {
"script": {
"source": """
String targetUser = params.key; <--- I don't know how to get the key here
int i = 0;
for (def user: doc.users) {
if (user == targetUser) break;
i++;
}
return doc.scores[i];
"""
}
}
}
}
}
}
}
}
}
}
}
Expected result:
{
"aggregations": {
"aggByDate": {
"buckets": [
{
"key_as_string": "2022-08-11T00:00:00.000+08:00",
"doc_count": 1,
"aggByGame": {
"buckets": [
{
"key": "game01",
"doc_count": 1,
"aggByUser": {
"buckets": [
{
"key": "user01", <--- this is the value I want to inject into the script
"doc_count": 1,
"totalScore": {
"value": 4
}
},
{
"key": "user02",
"doc_count": 1,
"totalScore": {
"value": 1
}
}
]
}
}
]
}
},
{
"key_as_string": "2022-08-12T00:00:00.000+08:00",
"doc_count": 2,
"aggByGame": {
"buckets": [
{
"key": "game02",
"doc_count": 1,
"aggByUser": {
"buckets": [
{
"key": "user01",
"doc_count": 1,
"totalScore": {
"value": 3
}
},
{
"key": "user02",
"doc_count": 2,
"totalScore": {
"value": 3
}
},
{
"key": "user03",
"doc_count": 1,
"totalScore": {
"value": 4
}
}
]
}
}
]
}
}
]
}
}
}
But since I don't know the userId before the query, I don't know where can I let elasticsearch inject the params.key into the script in the middle of the query.
I also referenced the issue here. Seems it's not possible to access the aggregation data for sub-aggs. Do we have another workaround here? Thanks!!
(I use ElasticSearch v7.10)