I have a locals variable defined as so:

locals {
  subnets = {
    # AWS Account:
    "222222222222" = {
      # Environment name:
      "prod" = {
        "us-west-2" : ["subnet-11111111111", "subnet-22222222", "subnet-3333333", "subnet-333333"]
      }
      "default" = {
        "us-east-2" : split(",", data.terraform_remote_state.vpc.outputs.private_subnets)
      }
    }
  }
}

# and I can reference it like so:
subnet_ids = local.subnets[var.aws_account_id][var.environment][var.region]

Unfortunately, the only two possible keys for var.enviroment is “prod” or “default”.

What I really want to do is: (pseudo code):

if var.environment is not a key in local.subnets[var.aws_account_id], then use the "default" value for var.environment.

Is this possible in terraform?