Logstash - How to copy a field into an array - logstash

Question

I am using logstash 5.6
In my document, I have a subfield "[emailHeaders][reingested-on]", and another field called [attributes], which contains several subfields [string], [double], each of which are arrays. :
{
"emailHeaders": {
"reingested-on": ["1613986076000"]
},
"attributes": {
"string": [
{
"name": "attributeString1",
"value": "attributeStringValue1"
},
{
"name": "attributeString2",
"value": "attributeStringValue2"
}
],
"double": [
{
"name": "attributeDouble1",
"value": 1.0
}
]
}
}
If the element [emailHeaders][reingested-on] is present in the document, I want to copy 1613986076000 (ie. the first element of [emailHeaders][reingested-on]) into [attributes][date] as follows:
{
"emailHeaders": {
"reingested-on": ["1613986076000"]
},
"attributes": {
"string": [
{
"name": "attributeString1",
"value": "attributeStringValue1"
},
{
"name": "attributeString2",
"value": "attributeStringValue2"
}
],
"double": [
{
"name": "attributeDouble1",
"value": 1.0
}
],
"date": [
{
"name": "Reingested on",
"value": 1613986076000
}
]
}
}
Note that if [attributes][date] already exists, and already contains an array of name/value pairs, I want my new object to be appended to the array.
Also, note that [attributes][date] is an array of objects which contain a date in their [value] attribute, as per the mapping of my ElasticSearch index:
...
"attributes": {
"properties": {
...
"date": {
"type": "nested",
"properties": {
"id": {"type": "keyword"},
"name": {"type": "keyword"},
"value": {"type": "date"}
}
},
...
}
},
...
I tried the following logstash configuration, with no success:
filter {
# See https://stackoverflow.com/questions/30309096/logstash-check-if-field-exists : this is supposed to allow to "test" if [#metadata][reingested-on] exists
mutate {
add_field => { "[#metadata][reingested-on]" => "None" }
copy => { "[emailHeaders][reingested-on][0]" => "[#metadata][reingested-on]" }
}
if [#metadata][reingested-on] != "None" {
# See https://stackoverflow.com/questions/36127961/append-array-of-json-logstash-elasticsearch: I create a temporary [error] field, and I try to append it to [attributes][date]
mutate {
add_field => { "[error][name]" => "Reingested on" }
add_field => { "[error][value]" => "[#metadata][reingested-on]" }
}
mutate {
merge => {"[attributes][date]" => "[error]"}
}
}
}
But what I get is:
{
"emailHeaders": {
"reingested-on": ["1613986076000"]
},
"error": {
"name": "Reingested on",
"value": "[#metadata][reingested-on]"
},
"attributes": {
"string": [
{
"name": "attributeString1",
"value": "attributeStringValue1"
},
{
"name": "attributeString2",
"value": "attributeStringValue2"
}
],
"double": [
{
"name": "attributeDouble1",
"value": 1.0
}
]
}
}
My temporary [error] object is created, but its value is wrong: it should be 1613986076000 instead of [#metadata][reingested-on]
Also, it is not appended to the array [attribute][date]. In this example, this array does not exist, so I want it to be created with my temporary object as first element, as per the expected result above.