Join/merge 2 json depending on a conditional in Terraform - terraform

Question

I have 2 json files, in one I have policies and in the another one I have clusters with custom configurations, the thing is if a cluster has a policy_id key, it should be merged/join with the respective policy to get its default configurations, if not just returns the base cluster.
cluster.json
[
{
"name": "a",
"memory": 16
},
{
"name":"b",
"memory": 16,
"policy_id": 2
}
]
policies.json
[
{
"policy_id": 1,
"policy_name": "test",
"policy_cores" : 4
},
{
"policy_id": 2,
"policy_name": "test2",
"policy_cores" : 8
}
]
So the expected result should be something like this, the "a" cluster remains the same because doesn't have a policy_id key, the "b" cluster has its values and policy's values:
[
{
"name": "a",
"memory": 16
},
{
"name":"b",
"memory": 16,
"policy_id": 2,
"policy_name": "test2",
"policy_cores" : 8
}
]
I was trying to do it in the locals block code but I don't know how I can do nested for loops with the conditional. Sorry for the pseudo code, I code in Python so Terraform is so rare for me.
locals {
# get jsons
policies = jsondecode(file("${path.module}/policies.json"))
clusters = jsondecode(file("${path.module}/clusters.json"))
#pseudo-code to express the logic, sorry im still learning Terraform
aux_clusters = [
for cluster in local.clusters : {
if try(cluster.policy_id, null) != null : {
#if policy_id key exists, then merge with the respective policy
for k, v in local.policies : {
k => merge(v, cluster) if v.policy_id == cluster.policy_id
}
} else {
#if policy_id key doesnt exist just return the base cluster
cluster
}
}
]
}
Thank you...