From 90cfade62698c8c68fd82019b7955aa65bb001e8 Mon Sep 17 00:00:00 2001
From: Mitchell Hashimoto <mitchell.hashimoto@gmail.com>
Date: Thu, 30 Apr 2015 17:02:39 -0700
Subject: [PATCH] terraform: naive flatten

---
 terraform/transform_flatten.go | 43 ++++++++++++++++++++++++++++++++++
 1 file changed, 43 insertions(+)
 create mode 100644 terraform/transform_flatten.go

diff --git a/terraform/transform_flatten.go b/terraform/transform_flatten.go
new file mode 100644
index 000000000..93161ceab
--- /dev/null
+++ b/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
+}