rings: introduce RingID and its values

Signed-off-by: Alejandro Mery <amery@jpi.io>

pkg/rings/rings.go

@@ -11,6 +11,17 @@ import (
 )
 
 const (
+	// UnspecifiedRingID is the zero value of RingID and not considered
+	// valid.
+	UnspecifiedRingID RingID = iota
+	RingZeroID               // RingZeroID is the RingID for RingZero (backbone)
+	RingOneID                // RingOneID is the RingID for RingOne (local zone)
+	RingTwoID                // RingTwoID is the RingID for RingTwo (region services)
+	RingThreeID              // RingThreeID is the RingID for RingThree (region cluster pods)
+
+	// RingMax indicates the highest [Ring] identifier
+	RingMax = RingThreeID
+
 	// RegionMax indicates the highest number that can be used for a [RegionID].
 	RegionMax = (1 << 4) - 1
 	// ZoneMax indicates the highest number that can be used for a [ZoneID].
@@ -33,6 +44,21 @@ const (
 	RingThreeBits = 12
 )
 
+// RingID identifies a Ring
+type RingID int
+
+// Valid tells a [RingID] is within the valid range.
+func (n RingID) Valid() bool { return n > 0 && n <= RingMax }
+
+func (n RingID) String() string {
+	return idString(n)
+}
+
+// A Ring identifies what ring an address belongs to
+type Ring interface {
+	ID() RingID
+}
+
 // RegionID is the identifier of a region, valid between 1 and [RegionMax].
 type RegionID int