From 5adac1ce4c480a5a3353f3c77f1d9edb8d3260cc Mon Sep 17 00:00:00 2001
From: Felix van Oost <felix.vanoost@live.com>
Date: Fri, 11 Aug 2023 21:28:34 +0000
Subject: [PATCH] Add D2 layout engine option (#1570)

* Support ELK layout engine
* Add smoke test for D2 layout option
* Add D2 layout option to documentation
* Check for null 'layout' argument
---
 ci/tests/smoke.js                                   |  1 +
 docs/modules/setup/pages/diagram-options.adoc       |  6 ++++++
 .../src/main/java/io/kroki/server/service/D2.java   | 13 +++++++++----
 3 files changed, 16 insertions(+), 4 deletions(-)

diff --git a/ci/tests/smoke.js b/ci/tests/smoke.js
index ea569d44e..6cfc47731 100755
--- a/ci/tests/smoke.js
+++ b/ci/tests/smoke.js
@@ -39,6 +39,7 @@ const tests = [
   { engine: 'diagramsnet', file: 'diagramsnet-venn.xml', options: {}, outputFormat: ['svg', 'png'] },
   { engine: 'diagramsnet', file: 'diagramsnet-infography.xml', options: { id: 'foo' }, outputFormat: ['svg', 'png'] },
   { engine: 'd2', file: 'connections.d2', options: {}, outputFormat: ['svg'] },
+  { engine: 'd2', file: 'connections.d2', options: { layout: 'elk' }, outputFormat: ['svg'] },
   { engine: 'd2', file: 'connections.d2', options: { sketch: 'true' }, outputFormat: ['svg'] },
   { engine: 'wireviz', file: 'wireviz.yaml', options: {}, outputFormat: ['svg', 'png'] },
   { engine: 'tikz', file: 'periodic-table.tex', options: {}, outputFormat: ['jpeg', 'pdf', 'png', 'svg'] }
diff --git a/docs/modules/setup/pages/diagram-options.adoc b/docs/modules/setup/pages/diagram-options.adoc
index a808e3911..8375bb7b3 100644
--- a/docs/modules/setup/pages/diagram-options.adoc
+++ b/docs/modules/setup/pages/diagram-options.adoc
@@ -64,6 +64,12 @@ With flag set, option takes effect.
 
 |See: https://d2lang.com/tour/themes/
 
+|layout
+|
+* `dagre` (default)
+* `elk`
+|Use an alternate layout engine: https://d2lang.com/tour/layouts/
+
 |sketch
 |_flag_ +
 empty string ("")
diff --git a/server/src/main/java/io/kroki/server/service/D2.java b/server/src/main/java/io/kroki/server/service/D2.java
index 41703685a..c30769af8 100644
--- a/server/src/main/java/io/kroki/server/service/D2.java
+++ b/server/src/main/java/io/kroki/server/service/D2.java
@@ -89,21 +89,26 @@ public void convert(String sourceDecoded, String serviceName, FileFormat fileFor
   private byte[] d2(byte[] source, JsonObject options) throws IOException, InterruptedException, IllegalStateException {
     List<String> commands = new ArrayList<>();
     commands.add(binPath);
-    String value = options.getString("theme");
-    if (value != null) {
+    String theme = options.getString("theme");
+    if (theme != null) {
       int themeId = 0;
-      Integer builtinThemeId = builtinThemes.get(value.toLowerCase().replaceAll("\\s", "-"));
+      Integer builtinThemeId = builtinThemes.get(theme.toLowerCase().replaceAll("\\s", "-"));
       if (builtinThemeId != null) {
         themeId = builtinThemeId;
       } else {
         try {
-          themeId = Integer.parseInt(value, 10);
+          themeId = Integer.parseInt(theme, 10);
         } catch (NumberFormatException e) {
           // ignore, fallback to 0
         }
       }
       commands.add("--theme=" + themeId);
     }
+    String layout = options.getString("layout");
+    if (layout != null && layout.equals("elk")) {
+      // Only pass the layout argument if the ELK layout engine is requested (default is 'dagre')
+      commands.add("--layout=" + layout);
+    }
     String sketch = options.getString("sketch");
     if (sketch != null) {
       commands.add("--sketch");