zones: introduce RingInfo.Merge()

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

pkg/zones/rings.go

@@ -1,6 +1,7 @@
 package zones
 
 import (
+	"fmt"
 	"net/netip"
 
 	"git.jpi.io/amery/jpictl/pkg/wireguard"
@@ -24,6 +25,73 @@ type RingInfo struct {
 	Address netip.Addr         `toml:"address,omitempty"`
 }
 
+// Merge attempts to combine two RingInfo structs
+func (ri *RingInfo) Merge(alter *RingInfo) error {
+	switch {
+	case ri.Ring != alter.Ring:
+		// different ring
+		return fmt.Errorf("invalid %s: %v ≠ %v", "ring", ri.Ring, alter.Ring)
+	case ri.Enabled != alter.Enabled:
+		// different state
+		return fmt.Errorf("invalid %s: %v ≠ %v", "enabled", ri.Enabled, alter.Enabled)
+	case !canMergeAddress(ri.Address, alter.Address):
+		// different address
+		return fmt.Errorf("invalid %s: %v ≠ %v", "address", ri.Address, alter.Address)
+	case !canMergeKeyPairs(ri.Keys, alter.Keys):
+		// incompatible keypairs
+		return fmt.Errorf("invalid %s: %s ≠ %s", "keys", ri.Keys, alter.Keys)
+	}
+
+	switch {
+	case ri.Keys == nil:
+		// assign keypair
+		ri.Keys = alter.Keys
+	case alter.Keys != nil:
+		// fill the gaps on our keypair
+		if ri.Keys.PrivateKey.IsZero() {
+			ri.Keys.PrivateKey = alter.Keys.PrivateKey
+		}
+		if ri.Keys.PublicKey.IsZero() {
+			ri.Keys.PublicKey = alter.Keys.PublicKey
+		}
+	}
+
+	if addressEqual(ri.Address, netip.Addr{}) {
+		// assign address
+		ri.Address = alter.Address
+	}
+
+	return nil
+}
+
+func canMergeAddress(ip1, ip2 netip.Addr) bool {
+	var zero netip.Addr
+
+	switch {
+	case addressEqual(ip1, zero) || addressEqual(ip2, zero) || addressEqual(ip1, ip2):
+		return true
+	default:
+		return false
+	}
+}
+
+func addressEqual(ip1, ip2 netip.Addr) bool {
+	return ip1.Compare(ip2) == 0
+}
+
+func canMergeKeyPairs(p1, p2 *wireguard.KeyPair) bool {
+	switch {
+	case p1 == nil || p2 == nil:
+		return true
+	case !p1.PrivateKey.IsZero() && !p2.PrivateKey.IsZero() && !p1.PrivateKey.Equal(p2.PrivateKey):
+		return false
+	case !p1.PublicKey.IsZero() && !p2.PublicKey.IsZero() && !p1.PublicKey.Equal(p2.PublicKey):
+		return false
+	default:
+		return true
+	}
+}
+
 // RingAddressEncoder provides encoder/decoder access for a particular
 // Wireguard ring
 type RingAddressEncoder struct {