add nested layout design

d2layouts/d2layouts.go

@@ -0,0 +1,61 @@
+package d2layouts
+
+import "oss.terrastruct.com/d2/d2graph"
+
+func LayoutNested(g *d2graph.Graph, graphType string, coreLayout d2graph.LayoutGraph) {
+	// Before we can layout these nodes, we need to handle all nested diagrams first.
+	extracted := make(map[*d2graph.Object]*d2graph.Graph)
+
+	// Iterate top-down from Root so all nested diagrams can process their own contents
+	queue := make([]*d2graph.Object, 0, len(g.Root.ChildrenArray))
+	queue = append(queue, g.Root.ChildrenArray...)
+
+	for _, child := range queue {
+		if graphType := NestedGraphType(child); graphType != nil {
+			// There is a nested diagram here, so extract its contents and process in the same way
+			nestedGraph := ExtractNested(child)
+
+			// Layout of nestedGraph is completed
+			LayoutNested(nestedGraph, *graphType, coreLayout)
+
+			// Fit child to size of nested layout
+			FitToGraph(child, nestedGraph)
+
+			// We will restore the contents after running layout with child as the placeholder
+			extracted[child] = nestedGraph
+		} else if len(child.Children) > 0 {
+			queue = append(queue, child.ChildrenArray...)
+		}
+	}
+
+	// We can now run layout with accurate sizes of nested layout containers
+	// Layout according to the type of diagram
+	LayoutDiagram(g, graphType, coreLayout)
+
+	// With the layout set, inject all the extracted graphs
+	for n, nestedGraph := range extracted {
+		InjectNested(n, nestedGraph)
+	}
+}
+
+func NestedGraphType(container *d2graph.Object) *string {
+	// TODO
+	return nil
+}
+
+func ExtractNested(container *d2graph.Object) *d2graph.Graph {
+	// TODO
+	return nil
+}
+
+func InjectNested(container *d2graph.Object, graph *d2graph.Graph) {
+	// TODO
+}
+
+func FitToGraph(container *d2graph.Object, graph *d2graph.Graph) {
+	// TODO
+}
+
+func LayoutDiagram(graph *d2graph.Graph, graphType string, coreLayout d2graph.LayoutGraph) {
+	// TODO
+}