package rings

import "net/netip"

// RingZeroPrefix represents the backbone that connects gateways
// of the different Ring 1 networks.
//
// The ring 0 network corresponds to what would be ring 2 for region_id 0.
// 10.0.0.0-10.0.255.255
func RingZeroPrefix(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 := unsafeRingZeroAddress(region, zone, 0)
		cidr = netip.PrefixFrom(addr, RingZeroBits)
	}

	return cidr, err
}

// RingZeroAddress returns a Ring 0 address for a particular node.
//
// A ring 0 address looks like 10.0.(region_id << 4 + zone_id).(node_id)/20
func RingZeroAddress(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.ValidZero():
		err = ErrOutOfRange(node, "node")
	default:
		addr = unsafeRingZeroAddress(region, zone, node)
	}

	return addr, err
}

// 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
}

// RingThreePrefix returns the subnet corresponding to
// the pods of a cluster.
//
// Ring 3 is a `10.(region_id << 4).0.0/12` network
func RingThreePrefix(region RegionID) (subnet netip.Prefix, err error) {
	switch {
	case !region.Valid():
		err = ErrOutOfRange(region, "region")
	default:
		addr := unsafeRingThreeAddress(region, 0)
		subnet = netip.PrefixFrom(addr, RingThreeBits)
	}
	return subnet, err
}

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

	return AddrFrom4(10, 0, r<<4+z, n)
}
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)
}

func unsafeRingThreeAddress(region RegionID, n uint) netip.Addr {
	r := uint(region)

	n2 := n >> 16
	n1 := n >> 8
	n0 := n >> 0

	return AddrFrom4(10, r<<4+n2, n1, n0)
}