feat(agent): diff inventories and debounce docker events

internal/agent/inventory/diff.go

@@ -0,0 +1,25 @@
+package inventory
+
+import "github.com/shcizo/package-updater/internal/protocol"
+
+// Diff compares two snapshots. upserts holds services that are new or
+// changed in next; removes holds the keys of services missing from next.
+func Diff(prev, next []protocol.Service) (upserts []protocol.Service, removes []string) {
+	old := make(map[string]protocol.Service, len(prev))
+	for _, s := range prev {
+		old[s.Key()] = s
+	}
+	seen := make(map[string]struct{}, len(next))
+	for _, s := range next {
+		seen[s.Key()] = struct{}{}
+		if o, ok := old[s.Key()]; !ok || o != s {
+			upserts = append(upserts, s)
+		}
+	}
+	for _, s := range prev {
+		if _, ok := seen[s.Key()]; !ok {
+			removes = append(removes, s.Key())
+		}
+	}
+	return upserts, removes
+}