Transform JSON file to add keys to array values - json

Question

I am using Apache NiFi and receive from an embedded micro over a TCP/IP socket a JSON file of the form:
{
"id": 123456,
"ip": "192.168.1.1",
"t": -12.9,
"T": -23.8,
"variables": [
"user1",
0,
-12.97,
23.87
]
}
and would like to transform it such that the keys of the variables are added as they are known to me as follows:
{
"id": 123456,
"ip": "192.168.1.1",
"t": -12.9,
"T": -23.8,
"variables": [
"username" : "user1",
"valid" : 0,
"temperature 1" : -12.97,
"temperature 2" : 23.87
]
}
and then to be able to access a key value pair such as variables.username.
I have tried using JoltTransformJSON but don't know how to write the spec correctly if it can do it!! I have written the following jolt spec:
[
{
"operation": "shift",
"spec": {
"id": "id",
"ip": "ip",
"t": "t",
"T": "T",
"variables": {
"username": "",
"valid": "",
"temperature 1": "",
"temperature 2": ""
}
}
}
]
I also have tried using UpdateRecord with Record Reader/Writer but passing the correct schema causes an error on the first variable as it can't match "user1" with a key from the initial JSON.

Answer 1

I have managed to work out the Jolt Spec as follows:
[
{
"operation": "shift",
"spec": {
"id": "id",
"ip": "ip",
"t": "t",
"T": "T",
"variables": {
"0": "username",
"1": "valid",
"2": "temperature 1",
"3": "temperature 2"
}
}
}
]
Thank you daggett for your contribution.