locals {
  netmask_to_prefix = {
    "0.0.0.0"         = 0
    "128.0.0.0"       = 1
    "192.0.0.0"       = 2
    "224.0.0.0"       = 3
    "240.0.0.0"       = 4
    "248.0.0.0"       = 5
    "252.0.0.0"       = 6
    "254.0.0.0"       = 7
    "255.0.0.0"       = 8
    "255.128.0.0"     = 9
    "255.192.0.0"     = 10
    "255.224.0.0"     = 11
    "255.240.0.0"     = 12
    "255.248.0.0"     = 13
    "255.252.0.0"     = 14
    "255.254.0.0"     = 15
    "255.255.0.0"     = 16
    "255.255.128.0"   = 17
    "255.255.192.0"   = 18
    "255.255.224.0"   = 19
    "255.255.240.0"   = 20
    "255.255.248.0"   = 21
    "255.255.252.0"   = 22
    "255.255.254.0"   = 23
    "255.255.255.0"   = 24
    "255.255.255.128" = 25
    "255.255.255.192" = 26
    "255.255.255.224" = 27
    "255.255.255.240" = 28
    "255.255.255.248" = 29
    "255.255.255.252" = 30
    "255.255.255.254" = 31
    "255.255.255.255" = 32
  }
  prefix_length  = lookup(local.netmask_to_prefix, var.cobbler_netmask, 24)
  host_bits      = 32 - local.prefix_length
  total_hosts    = pow(2, local.host_bits)
  last_usable_ip = local.total_hosts - 2

  # derive subnet base from instance IP
  cidr_block = cidrsubnet("${incus_instance.this.ipv4_address}/${local.prefix_length}", 0, 0)

  # get the last usable IP
  gateway_ip = cidrhost(local.cidr_block, local.last_usable_ip)
}