allow to use custom workflow template for generatig diagrams

Signed-off-by: Maciej Swiderski <swiderski.maciej@gmail.com>

Author: mswiderski

README.md

@@ -267,6 +267,22 @@ String diagramSVG = workflowDiagram.getSvgDiagram();
 `diagramSVG` includes the diagram SVG source which you can then decide to save to a file, 
 print, or process further.
 
+In case default visualization of the workflow is not sufficient you can provide custom workflow template to be 
+used while generating the SVG file. Easiest is to start off from the default template and customize it to your needs.
+
+Custom template must be on the classpath in `templates/plantuml` directory and must use `.txt` extension. Next
+template is set on `WorkflowDiagram` instance as shown below.
+
+``` java
+Workflow workflow = Workflow.fromSource(source);
+
+WorkflowDiagram workflowDiagram = new WorkflowDiagramImpl();
+workflowDiagram.setWorkflow(workflow);
+workflowDiagram.setTemplate("custom-template");
+
+String diagramSVG = workflowDiagram.getSvgDiagram();
+```
+
 By default the diagram legend is now shown. If you want to enable it you can do:
 
 ``` java

api/src/main/java/io/serverlessworkflow/api/interfaces/WorkflowDiagram.java

@@ -22,6 +22,8 @@ public interface WorkflowDiagram {
 
   WorkflowDiagram setSource(String source);
 
+  WorkflowDiagram setTemplate(String template);
+
   String getSvgDiagram() throws Exception;
 
   WorkflowDiagram showLegend(boolean showLegend);

diagram/src/main/java/io/serverlessworkflow/diagram/WorkflowDiagramImpl.java

@@ -26,9 +26,14 @@
 
 public class WorkflowDiagramImpl implements WorkflowDiagram {
 
+  public static final String DEFAULT_TEMPLATE = "workflow-template";
+
   @SuppressWarnings("unused")
   private String source;
 
+  @SuppressWarnings("unused")
+  private String template = DEFAULT_TEMPLATE;
+
   private Workflow workflow;
   private boolean showLegend = false;
 
@@ -46,12 +51,18 @@ public WorkflowDiagram setSource(String source) {
     return this;
   }
 
+  @Override
+  public WorkflowDiagram setTemplate(String template) {
+    this.template = template;
+    return this;
+  }
+
   @Override
   public String getSvgDiagram() throws Exception {
     if (workflow == null) {
       throw new IllegalAccessException("Unable to get diagram - no workflow set.");
     }
-    String diagramSource = WorkflowToPlantuml.convert(workflow, showLegend);
+    String diagramSource = WorkflowToPlantuml.convert(template, workflow, showLegend);
     SourceStringReader reader = new SourceStringReader(diagramSource);
     final ByteArrayOutputStream os = new ByteArrayOutputStream();
     reader.generateImage(os, new FileFormatOption(FileFormat.SVG));

diagram/src/main/java/io/serverlessworkflow/diagram/utils/WorkflowToPlantuml.java

@@ -22,11 +22,12 @@
 import org.thymeleaf.context.Context;
 
 public class WorkflowToPlantuml {
-  public static String convert(Workflow workflow, boolean showLegend) {
+
+  public static String convert(String template, Workflow workflow, boolean showLegend) {
     TemplateEngine plantUmlTemplateEngine = ThymeleafConfig.templateEngine;
     Context context = new Context();
     context.setVariable("diagram", new WorkflowDiagramModel(workflow, showLegend));
 
-    return plantUmlTemplateEngine.process("workflow-template", context);
+    return plantUmlTemplateEngine.process(template, context);
   }
 }

diagram/src/test/java/io/serverlessworkflow/diagram/test/CustomTemplateWorkflowDiagramTest.java

@@ -0,0 +1,50 @@
+/*
+ * Copyright 2020-Present The Serverless Workflow Specification Authors
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package io.serverlessworkflow.diagram.test;
+
+import static org.junit.jupiter.api.Assertions.assertNotNull;
+
+import io.serverlessworkflow.api.Workflow;
+import io.serverlessworkflow.api.interfaces.WorkflowDiagram;
+import io.serverlessworkflow.diagram.WorkflowDiagramImpl;
+import io.serverlessworkflow.diagram.test.utils.DiagramTestUtils;
+import org.junit.jupiter.api.Assertions;
+import org.junit.jupiter.params.ParameterizedTest;
+import org.junit.jupiter.params.provider.ValueSource;
+
+public class CustomTemplateWorkflowDiagramTest {
+
+  @ParameterizedTest
+  @ValueSource(strings = {"/examples/applicantrequest.json", "/examples/applicantrequest.yml"})
+  public void testSpecExamplesParsing(String workflowLocation) throws Exception {
+
+    Workflow workflow = Workflow.fromSource(DiagramTestUtils.readWorkflowFile(workflowLocation));
+
+    assertNotNull(workflow);
+    assertNotNull(workflow.getId());
+    assertNotNull(workflow.getName());
+    assertNotNull(workflow.getStates());
+
+    WorkflowDiagram workflowDiagram =
+        new WorkflowDiagramImpl().setWorkflow(workflow).setTemplate("custom-template");
+
+    String diagramSVG = workflowDiagram.getSvgDiagram();
+
+    Assertions.assertNotNull(diagramSVG);
+    // custom template uses #0000FF as start node color
+    Assertions.assertTrue(diagramSVG.contains("#0000FF"));
+  }
+}

diagram/src/test/resources/templates/plantuml/custom-template.txt

@@ -0,0 +1,46 @@
+@startuml
+skinparam backgroundColor White
+skinparam legendBackgroundColor White
+skinparam legendBorderColor White
+skinparam state {
+  StartColor #0000FF
+  EndColor Orange
+  BackgroundColor GhostWhite
+  BackgroundColor<< workflow >> White
+  BorderColor Black
+  ArrowColor Black
+
+  BorderColor<< event >> #7fe5f0
+  BorderColor<< operation >> #bada55
+  BorderColor<< switch >> #92a0f2
+  BorderColor<< sleep >> #b83b5e
+  BorderColor<< parallel >> #6a2c70
+  BorderColor<< inject >> #1e5f74
+  BorderColor<< foreach >> #931a25
+  BorderColor<< callback >> #ffcb8e
+}
+state "[(${diagram.title})]" as workflow << workflow >> {
+
+[# th:each="stateDef : ${diagram.modelStateDefs}" ]
+[(${stateDef.toString()})]
+[/]
+
+[# th:each="state : ${diagram.modelStates}" ]
+[(${state.toString()})]
+[/]
+
+[# th:each="connection : ${diagram.modelConnections}" ]
+[(${connection.toString()})]
+[/]
+
+}
+
+[# th:if="${diagram.showLegend}" ]
+legend center
+State Types and Border Colors:
+| Event | Operation | Switch | Sleep | Parallel | Inject | ForEach | CallBack |
+|<#7fe5f0>|<#bada55>|<#92a0f2>|<#b83b5e>|<#6a2c70>|<#1e5f74>|<#931a25>|<#ffcb8e>|
+endlegend
+[/]
+
+@enduml