Conditionally set a variable in a aws_s3_bucket resource

Terraform
1

We can create a resource based on count like

resource "aws_s3_bucket" "mybucket" {
count = var.enabled ? 1 : 0
...

That is ok but I need something more.

aws_s3_bucket has two different options for the bucket name
bucket or bucket_prefix

They are conflict with each other.

I would like to have a variable like create_bucket_with_static_name

If  create_bucket_with_static_name  true
 then 
   set  bucket = var.bucket_name
else
   set bucket_prefix = var.bucket_prefix_value

Is this doable in a single aws_s3_bucket resource? or Do I have to create two different aws_s3_bucket resource one for bucket and other for bucket_prefix set?