feat: generate fallback cache snapshot excluding affected objects

internal/dataplane/fallback/cache_to_graph.go

@@ -0,0 +1,62 @@
+package fallback
+
+import (
+	"errors"
+	"fmt"
+
+	"github.com/dominikbraun/graph"
+	"sigs.k8s.io/controller-runtime/pkg/client"
+
+	"github.com/kong/kubernetes-ingress-controller/v3/internal/store"
+)
+
+// DefaultCacheGraphProvider is a default implementation of the CacheGraphProvider interface.
+type DefaultCacheGraphProvider struct{}
+
+func NewDefaultCacheGraphProvider() *DefaultCacheGraphProvider {
+	return &DefaultCacheGraphProvider{}
+}
+
+// CacheToGraph creates a new ConfigGraph from the given cache stores. It adds all objects
+// from the cache stores to the graph as vertices as well as edges between objects and their dependencies
+// resolved by the ResolveDependencies function.
+func (p DefaultCacheGraphProvider) CacheToGraph(c store.CacheStores) (*ConfigGraph, error) {
+	g := NewConfigGraph()
+
+	for _, s := range c.ListAllStores() {
+		for _, o := range s.List() {
+			obj, ok := o.(client.Object)
+			if !ok {
+				// Should not happen since all objects in the cache are client.Objects, but better safe than sorry.
+				return nil, fmt.Errorf("expected client.Object, got %T", o)
+			}
+			// Add the object to the graph. It can happen that the object is already in the graph (i.e. was already added
+			// as a dependency of another object), in which case we ignore the error.
+			if err := g.AddVertex(obj); err != nil && !errors.Is(err, graph.ErrVertexAlreadyExists) {
+				return nil, fmt.Errorf("failed to add %s to the graph: %w", GetObjectHash(obj), err)
+			}
+
+			deps, err := ResolveDependencies(c, obj)
+			if err != nil {
+				return nil, fmt.Errorf("failed to resolve dependencies for %s: %w", GetObjectHash(obj), err)
+			}
+			// Add the object's dependencies to the graph.
+			for _, dep := range deps {
+				// Add the dependency to the graph in case it wasn't added before. If it was added before, we ignore the
+				// error.
+				if err := g.AddVertex(dep); err != nil && !errors.Is(err, graph.ErrVertexAlreadyExists) {
+					return nil, fmt.Errorf("failed to add %s to the graph: %w", GetObjectHash(obj), err)
+				}
+
+				// Add an edge from a dependency to the object. If the edge was already added before, we ignore the error.
+				// It's on purpose that we add the edge from the dependency to the object, as it makes it easier to traverse
+				// the graph from the object to its dependants once it is broken.
+				if err := g.AddEdge(GetObjectHash(dep), GetObjectHash(obj)); err != nil && !errors.Is(err, graph.ErrEdgeAlreadyExists) {
+					return nil, fmt.Errorf("failed to add edge from %s to %s: %w", GetObjectHash(obj), GetObjectHash(dep), err)
+				}
+			}
+		}
+	}
+
+	return g, nil
+}