From 5526276c6654748d88726807b681f2a26e6d5a8f Mon Sep 17 00:00:00 2001
From: Alejandro Mery <amery@jpi.io>
Date: Sun, 19 May 2024 02:11:02 +0000
Subject: [PATCH] rings: WIP

Signed-off-by: Alejandro Mery <amery@jpi.io>
---
 pkg/rings/errors.go |  11 ++++
 pkg/rings/rings.go  | 127 ++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 138 insertions(+)
 create mode 100644 pkg/rings/errors.go
 create mode 100644 pkg/rings/rings.go

diff --git a/pkg/rings/errors.go b/pkg/rings/errors.go
new file mode 100644
index 0000000..e66f79b
--- /dev/null
+++ b/pkg/rings/errors.go
@@ -0,0 +1,11 @@
+package rings
+
+import (
+	"syscall"
+
+	"darvaza.org/core"
+)
+
+func ErrOutOfRange[T ~int](value T, field string) error {
+	return core.Wrap(syscall.EINVAL, "%v: %s out of range", value, field)
+}
diff --git a/pkg/rings/rings.go b/pkg/rings/rings.go
new file mode 100644
index 0000000..41e973a
--- /dev/null
+++ b/pkg/rings/rings.go
@@ -0,0 +1,127 @@
+// Package rings implements ...
+package rings
+
+import (
+	"net/netip"
+)
+
+const (
+	RegionBits   = 4
+	ZoneBits     = 4
+	NodeBits     = 12
+	NodeZeroBits = 8
+
+	RegionMax   = (1 << RegionBits) - 1
+	ZoneMax     = (1 << ZoneBits) - 1
+	NodeMax     = (1 << NodeBits) - 1
+	NodeZeroMax = (1 << NodeZeroBits) - 1
+
+	RingZeroBits  = 20
+	RingOneBits   = 20
+	RingTwoBits   = 20
+	RingThreeBits = 12
+)
+
+type (
+	RegionID int
+	ZoneID   int
+	NodeID   int
+)
+
+func (n RegionID) Valid() bool   { return n > 0 && n <= RegionMax }
+func (n ZoneID) Valid() bool     { return n > 0 && n <= ZoneMax }
+func (n NodeID) Valid() bool     { return n > 0 && n <= NodeMax }
+func (n NodeID) ValidZero() bool { return n > 0 && n <= NodeZeroMax }
+
+// 10.0.(region_id << 4 + zone_id).(node_id)/20 for ring 0
+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 = unsafeAddrFrom4(10, 0, uint(region)<<4+uint(zone), uint(node))
+	}
+
+	return addr, err
+}
+
+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 := unsafeAddrFrom4(10, 0, uint(region)<<4+uint(zone), 0)
+		cidr = netip.PrefixFrom(addr, RingZeroBits)
+	}
+
+	return cidr, err
+}
+
+// 10.(region_id).(zone_id << 4).(node_id)/20 for ring 1
+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:
+		n1 := uint(node) / 8
+		n2 := uint(node) % 8
+		addr = unsafeAddrFrom4(10, uint(region), uint(zone)<<4+n1, n2)
+	}
+	return addr, err
+}
+
+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 := unsafeAddrFrom4(10, uint(region), uint(zone)<<4, 0)
+		cidr = netip.PrefixFrom(addr, RingOneBits)
+	}
+	return cidr, err
+}
+
+// 10.(region_id).0.0/20 for ring 2
+func RingTwoPrefix(region RegionID) (cidr netip.Prefix, err error) {
+	switch {
+	case !region.Valid():
+		err = ErrOutOfRange(region, "region")
+	default:
+		addr := unsafeAddrFrom4(10, uint(region), 0, 0)
+		cidr = netip.PrefixFrom(addr, RingTwoBits)
+	}
+	return cidr, err
+}
+
+// 10.(region_id << 4).0.0/12 for ring 3
+func RingThreePrefix(region RegionID) (cidr netip.Prefix, err error) {
+	switch {
+	case !region.Valid():
+		err = ErrOutOfRange(region, "region")
+	default:
+		addr := unsafeAddrFrom4(10, uint(region)<<4, 0, 0)
+		cidr = netip.PrefixFrom(addr, RingThreeBits)
+	}
+	return cidr, err
+}
+
+func unsafeAddrFrom4[T ~int | ~uint](a, b, c, d T) netip.Addr {
+	return netip.AddrFrom4([4]byte{
+		byte(a),
+		byte(b),
+		byte(c),
+		byte(d),
+	})
+}