terraform: naive flatten

terraform/transform_flatten.go

@@ -0,0 +1,43 @@
+package terraform
+
+// GraphNodeFlattenable must be implemented by nodes that can be flattened
+// into the graph.
+type GraphNodeFlattenable interface {
+	GraphNodeSubgraph
+
+	// Flatten should return true if this should be flattened.
+	Flatten() bool
+}
+
+// FlattenTransform is a transformer that goes through the graph, finds
+// subgraphs that can be flattened, and flattens them into this graph,
+// removing the prior subgraph node.
+type FlattenTransform struct{}
+
+func (t *FlattenTransform) Transform(g *Graph) error {
+	for _, v := range g.Vertices() {
+		fn, ok := v.(GraphNodeFlattenable)
+		if !ok {
+			continue
+		}
+
+		// If we don't want to be flattened, don't do it
+		if !fn.Flatten() {
+			continue
+		}
+
+		// Get the subgraph and flatten it into this one
+		subgraph := fn.Subgraph()
+		for _, sv := range subgraph.Vertices() {
+			g.Add(sv)
+		}
+		for _, se := range subgraph.Edges() {
+			g.Connect(se)
+		}
+
+		// Remove the old node
+		g.Remove(v)
+	}
+
+	return nil
+}