package rings

import "net/netip"

// RingOnePrefix represents a (virtual) local network of a zone.
//
// Ring 1 is `10.(region_id).(zone_id << 4).(node_id)/20` network
// grouped under what would be Ring 2 for region_id 0.
// There are 12 bits worth of nodes but nodes under 255 are special
// as they also get a slot on Ring 0.
func RingOnePrefix(region RegionID, zone ZoneID) (cidr netip.Prefix, err error) {
	switch {
	case !region.Valid():
		err = ErrOutOfRange(region, "region")
	case !zone.Valid():
		err = ErrOutOfRange(zone, "zone")
	default:
		addr := unsafeRingOneAddress(region, zone, 0)
		cidr = netip.PrefixFrom(addr, RingOneBits)
	}
	return cidr, err
}

// RingOneAddress returns a Ring 1 address for a particular node.
//
// A ring 1 address is `10.(region_id).(zone_id << 4).(node_id)/20`
// but the node_id can take up to 12 bits.
func RingOneAddress(region RegionID, zone ZoneID, node NodeID) (addr netip.Addr, err error) {
	switch {
	case !region.Valid():
		err = ErrOutOfRange(region, "region")
	case !zone.Valid():
		err = ErrOutOfRange(zone, "zone")
	case !node.Valid():
		err = ErrOutOfRange(node, "node")
	default:
		addr = unsafeRingOneAddress(region, zone, node)
	}
	return addr, err
}

func unsafeRingOneAddress(region RegionID, zone ZoneID, node NodeID) netip.Addr {
	r := uint(region)
	z := uint(zone)
	n := uint(node)

	n1 := n >> 8
	n0 := n >> 0

	return AddrFrom4(10, r, z<<4+n1, n0)
}