daemon: use per-interface features

Signed-off-by: Steffen Vogel <post@steffenvogel.de>

pkg/daemon/feature.go

@@ -0,0 +1,43 @@
+// Package feat contains several sub-packages each implementing a dedicated feature.
+package daemon
+
+import (
+	"golang.org/x/exp/slices"
+)
+
+var (
+	Features = map[string]*FeaturePlugin{}
+	plugins  []*FeaturePlugin
+)
+
+type FeaturePlugin struct {
+	Name        string
+	Description string
+
+	New   func(i *Interface) (Feature, error)
+	Order int
+}
+
+type SyncableFeature interface {
+	Sync() error
+}
+
+type Feature interface {
+	Start() error
+	Close() error
+}
+
+func SortedFeatures() []*FeaturePlugin {
+	if plugins == nil {
+		for name, feat := range Features {
+			feat.Name = name
+			plugins = append(plugins, feat)
+		}
+	}
+
+	slices.SortFunc(plugins, func(a, b *FeaturePlugin) bool {
+		return a.Order < b.Order
+	})
+
+	return plugins
+}