From b8355c7fa9c5a710e2ce1dda74837335e8925f82 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?J=C3=BAlio=20C=C3=A9sar=20Batista?= <julio@terrastruct.com>
Date: Mon, 28 Nov 2022 14:01:22 -0800
Subject: [PATCH] Add sequenceDiagram to hold values required to layout the
 diagram

---
 d2layouts/d2sequence/layout.go | 55 ++++++++++++++++++++--------------
 1 file changed, 33 insertions(+), 22 deletions(-)

diff --git a/d2layouts/d2sequence/layout.go b/d2layouts/d2sequence/layout.go
index 5d1107a39..870eaa622 100644
--- a/d2layouts/d2sequence/layout.go
+++ b/d2layouts/d2sequence/layout.go
@@ -12,53 +12,64 @@ import (
 )
 
 func Layout(ctx context.Context, g *d2graph.Graph) (err error) {
-	edgeYStep := MIN_EDGE_DISTANCE
-	actorXStep := MIN_ACTOR_DISTANCE
-	maxActorHeight := 0.
+	sd := &sequenceDiagram{
+		graph:          g,
+		edgeYStep:      MIN_EDGE_DISTANCE,
+		actorXStep:     MIN_ACTOR_DISTANCE,
+		maxActorHeight: 0.,
+	}
 
 	actorRank := make(map[*d2graph.Object]int)
 	for rank, actor := range g.Objects {
 		actorRank[actor] = rank
 	}
 	for _, edge := range g.Edges {
-		edgeYStep = math.Max(edgeYStep, float64(edge.LabelDimensions.Height)+HORIZONTAL_PAD)
-		maxActorHeight = math.Max(maxActorHeight, edge.Src.Height+HORIZONTAL_PAD)
-		maxActorHeight = math.Max(maxActorHeight, edge.Dst.Height+HORIZONTAL_PAD)
+		sd.edgeYStep = math.Max(sd.edgeYStep, float64(edge.LabelDimensions.Height)+HORIZONTAL_PAD)
+		sd.maxActorHeight = math.Max(sd.maxActorHeight, edge.Src.Height+HORIZONTAL_PAD)
+		sd.maxActorHeight = math.Max(sd.maxActorHeight, edge.Dst.Height+HORIZONTAL_PAD)
 		// ensures that long labels, spanning over multiple actors, don't make for large gaps between actors
 		// by distributing the label length across the actors rank difference
 		rankDiff := math.Abs(float64(actorRank[edge.Src]) - float64(actorRank[edge.Dst]))
 		distributedLabelWidth := float64(edge.LabelDimensions.Width) / rankDiff
-		actorXStep = math.Max(actorXStep, distributedLabelWidth+HORIZONTAL_PAD)
+		sd.actorXStep = math.Max(sd.actorXStep, distributedLabelWidth+HORIZONTAL_PAD)
 	}
 
-	placeActors(g.Objects, maxActorHeight, actorXStep)
-	routeEdges(g.Edges, maxActorHeight, edgeYStep)
-	addLifelineEdges(g, g.Objects, edgeYStep)
+	sd.placeActors()
+	sd.routeEdges()
+	sd.addLifelineEdges()
 
 	return nil
 }
 
+type sequenceDiagram struct {
+	graph *d2graph.Graph
+
+	edgeYStep      float64
+	actorXStep     float64
+	maxActorHeight float64
+}
+
 // placeActors places actors bottom aligned, side by side
-func placeActors(actors []*d2graph.Object, maxHeight, xStep float64) {
+func (sd *sequenceDiagram) placeActors() {
 	x := 0.
-	for _, actors := range actors {
-		yOffset := maxHeight - actors.Height
+	for _, actors := range sd.graph.Objects {
+		yOffset := sd.maxActorHeight - actors.Height
 		actors.TopLeft = geo.NewPoint(x, yOffset)
-		x += actors.Width + xStep
+		x += actors.Width + sd.actorXStep
 		actors.LabelPosition = go2.Pointer(string(label.InsideMiddleCenter))
 	}
 }
 
 // routeEdges routes horizontal edges from Src to Dst
-func routeEdges(edgesInOrder []*d2graph.Edge, startY, yStep float64) {
-	edgeY := startY + yStep // in case the first edge has a tall label
-	for _, edge := range edgesInOrder {
+func (sd *sequenceDiagram) routeEdges() {
+	edgeY := sd.maxActorHeight + sd.edgeYStep // in case the first edge has a tall label
+	for _, edge := range sd.graph.Edges {
 		start := edge.Src.Center()
 		start.Y = edgeY
 		end := edge.Dst.Center()
 		end.Y = edgeY
 		edge.Route = []*geo.Point{start, end}
-		edgeY += yStep
+		edgeY += sd.edgeYStep
 
 		if edge.Attributes.Label.Value != "" {
 			isLeftToRight := edge.Src.TopLeft.X < edge.Dst.TopLeft.X
@@ -80,14 +91,14 @@ func routeEdges(edgesInOrder []*d2graph.Edge, startY, yStep float64) {
 //        │ lifeline
 //        │
 //        │
-func addLifelineEdges(g *d2graph.Graph, actors []*d2graph.Object, yStep float64) {
-	endY := g.Edges[len(g.Edges)-1].Route[0].Y + yStep
-	for _, actor := range actors {
+func (sd *sequenceDiagram) addLifelineEdges() {
+	endY := sd.graph.Edges[len(sd.graph.Edges)-1].Route[0].Y + sd.edgeYStep
+	for _, actor := range sd.graph.Objects {
 		actorBottom := actor.Center()
 		actorBottom.Y = actor.TopLeft.Y + actor.Height
 		actorLifelineEnd := actor.Center()
 		actorLifelineEnd.Y = endY
-		g.Edges = append(g.Edges, &d2graph.Edge{
+		sd.graph.Edges = append(sd.graph.Edges, &d2graph.Edge{
 			Attributes: d2graph.Attributes{
 				Style: d2graph.Style{
 					StrokeDash:  &d2graph.Scalar{Value: "10"},