Add core modules (SSH args parser, cache, resolver, NetBox client) with tests

internal/resolver/chain.go

@@ -0,0 +1,57 @@
+package resolver
+
+import (
+	"context"
+	"fmt"
+
+	"git.zb-server.de/Sebi/ssh-netbox-wrapper/internal/config"
+	"git.zb-server.de/Sebi/ssh-netbox-wrapper/internal/netbox"
+)
+
+// Chain tries each strategy in order until one returns an IP.
+type Chain struct {
+	strategies []Strategy
+}
+
+// New builds a Chain from the strategy names listed in the resolver config.
+func New(cfg config.ResolverConfig) (*Chain, error) {
+	var strategies []Strategy
+	for _, name := range cfg.Strategies {
+		s, err := newStrategy(name, cfg)
+		if err != nil {
+			return nil, fmt.Errorf("resolver strategy %q: %w", name, err)
+		}
+		strategies = append(strategies, s)
+	}
+	return &Chain{strategies: strategies}, nil
+}
+
+func (c *Chain) Resolve(ctx context.Context, entry *netbox.HostEntry, client *netbox.Client) (string, error) {
+	for _, s := range c.strategies {
+		ip, err := s.Resolve(ctx, entry, client)
+		if err == nil {
+			return ip, nil
+		}
+	}
+	return "", fmt.Errorf("no strategy resolved an IP for %q", entry.Name)
+}
+
+func newStrategy(name string, cfg config.ResolverConfig) (Strategy, error) {
+	switch name {
+	case "primary_ip":
+		return &PrimaryIPStrategy{}, nil
+	case "management_subnet":
+		s, err := NewManagementSubnetStrategy(cfg.ManagementSubnets)
+		if err != nil {
+			return nil, err
+		}
+		return s, nil
+	case "interface_name":
+		if cfg.InterfaceName == "" {
+			return nil, fmt.Errorf("interface_name strategy requires resolver.interface_name to be set")
+		}
+		return &InterfaceNameStrategy{name: cfg.InterfaceName}, nil
+	default:
+		return nil, fmt.Errorf("unknown strategy %q", name)
+	}
+}