split nodes.go into focused files and refactor Update function

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

link.go

@@ -0,0 +1,125 @@
+package tendrils
+
+import "fmt"
+
+type Link struct {
+	NodeA      *Node
+	InterfaceA string
+	NodeB      *Node
+	InterfaceB string
+}
+
+func (l *Link) String() string {
+	nameA := l.NodeA.DisplayName()
+	if nameA == "" {
+		nameA = l.NodeA.FirstMAC()
+	}
+	nameB := l.NodeB.DisplayName()
+	if nameB == "" {
+		nameB = l.NodeB.FirstMAC()
+	}
+	sideA := nameA
+	if l.InterfaceA != "" {
+		sideA = nameA + ":" + l.InterfaceA
+	}
+	sideB := nameB
+	if l.InterfaceB != "" {
+		sideB = nameB + ":" + l.InterfaceB
+	}
+	return fmt.Sprintf("%s <-> %s", sideA, sideB)
+}
+
+func (n *Nodes) getDirectLinks() []*Link {
+	macToNode := map[string]*Node{}
+	for _, node := range n.nodes {
+		for _, iface := range node.Interfaces {
+			if iface.MAC != nil {
+				macToNode[iface.MAC.String()] = node
+			}
+		}
+	}
+
+	seen := map[string]bool{}
+	var links []*Link
+
+	for _, target := range n.nodes {
+		seenMACs := map[string]bool{}
+		for _, iface := range target.Interfaces {
+			if iface.MAC == nil {
+				continue
+			}
+			mac := iface.MAC.String()
+			if seenMACs[mac] {
+				continue
+			}
+			seenMACs[mac] = true
+
+			lastHop, lastPort := n.findLastHop(target, mac, macToNode)
+			if lastHop == nil {
+				continue
+			}
+
+			targetIface := n.findTargetInterface(target, lastHop, macToNode)
+			key := makeLinkKey(lastHop, lastPort, target, targetIface)
+			if !seen[key] {
+				seen[key] = true
+				links = append(links, &Link{
+					NodeA:      lastHop,
+					InterfaceA: lastPort,
+					NodeB:      target,
+					InterfaceB: targetIface,
+				})
+			}
+		}
+	}
+
+	return links
+}
+
+func (n *Nodes) findLastHop(target *Node, mac string, macToNode map[string]*Node) (*Node, string) {
+	for _, node := range n.nodes {
+		port, sees := node.MACTable[mac]
+		if !sees || node == target {
+			continue
+		}
+
+		if !n.hasCloserNode(node, target, mac, port, macToNode) {
+			return node, port
+		}
+	}
+	return nil, ""
+}
+
+func (n *Nodes) hasCloserNode(node, target *Node, mac, port string, macToNode map[string]*Node) bool {
+	for otherMAC, otherPort := range node.MACTable {
+		if otherPort != port {
+			continue
+		}
+		otherNode := macToNode[otherMAC]
+		if otherNode == nil || otherNode == node || otherNode == target {
+			continue
+		}
+		if _, alsoSees := otherNode.MACTable[mac]; alsoSees {
+			return true
+		}
+	}
+	return false
+}
+
+func (n *Nodes) findTargetInterface(target, lastHop *Node, macToNode map[string]*Node) string {
+	for lastHopMAC, targetPort := range target.MACTable {
+		if macToNode[lastHopMAC] == lastHop {
+			return targetPort
+		}
+	}
+	return ""
+}
+
+func makeLinkKey(nodeA *Node, ifaceA string, nodeB *Node, ifaceB string) string {
+	ptrA := fmt.Sprintf("%p", nodeA)
+	ptrB := fmt.Sprintf("%p", nodeB)
+	if ptrA < ptrB {
+		return ptrA + ":" + ifaceA + "-" + ptrB + ":" + ifaceB
+	}
+	return ptrB + ":" + ifaceB + "-" + ptrA + ":" + ifaceA
+}