clarified TemplateService comments

We will keep this abstractions as it's convenient, otherwise IngestDocument would depend on ScriptService directly, and would explicitly rely on mustache which is not even part of core. better to have the interface in core, and the impl as part of the ingest plugin, which relies on mustache, shipped with core by default.

core/src/main/java/org/elasticsearch/ingest/TemplateService.java

@@ -21,10 +21,9 @@ package org.elasticsearch.ingest;
 import java.util.Map;
 
 /**
- * Abstraction for the template engine.
+ * Abstraction for the ingest template engine: allows to compile a template into a {@link Template} object.
+ * A compiled template can be executed by calling its {@link Template#execute(Map)} method.
  */
-// NOTE: this abstraction is added because the 'org.elasticsearch.ingest' has the requirement to be ES agnostic
-//TODO this abstraction could be removed once ingest-core is part of es core?
 public interface TemplateService {
 
     Template compile(String template);
@@ -34,7 +33,5 @@ public interface TemplateService {
         String execute(Map<String, Object> model);
 
         String getKey();
-
     }
-
 }

plugins/ingest/src/main/java/org/elasticsearch/plugin/ingest/IngestPlugin.java

@@ -170,6 +170,6 @@ public class IngestPlugin extends Plugin {
     }
 
     public void onModule(ScriptModule module) {
-        module.registerScriptContext(InternalTemplateService.INGEST_SCRIPT_CONTEXT);
+        module.registerScriptContext(MustacheTemplateService.INGEST_SCRIPT_CONTEXT);
     }
 }

plugins/ingest/src/main/java/org/elasticsearch/plugin/ingest/MustacheTemplateService.java

@@ -30,13 +30,13 @@ import org.elasticsearch.script.ScriptService;
 import java.util.Collections;
 import java.util.Map;
 
-class InternalTemplateService implements TemplateService {
+class MustacheTemplateService implements TemplateService {
 
     public static final ScriptContext.Plugin INGEST_SCRIPT_CONTEXT = new ScriptContext.Plugin("elasticsearch-ingest", "ingest");
 
     private final ScriptService scriptService;
 
-    InternalTemplateService(ScriptService scriptService) {
+    MustacheTemplateService(ScriptService scriptService) {
         this.scriptService = scriptService;
     }
 

plugins/ingest/src/main/java/org/elasticsearch/plugin/ingest/PipelineStore.java

@@ -87,7 +87,7 @@ public class PipelineStore extends AbstractComponent implements Closeable {
 
     public void buildProcessorFactoryRegistry(Map<String, ProcessorFactoryProvider> processorFactoryProviders, Environment environment, ScriptService scriptService) {
         Map<String, Processor.Factory> processorFactories = new HashMap<>();
-        TemplateService templateService = new InternalTemplateService(scriptService);
+        TemplateService templateService = new MustacheTemplateService(scriptService);
         for (Map.Entry<String, ProcessorFactoryProvider> entry : processorFactoryProviders.entrySet()) {
             Processor.Factory processorFactory = entry.getValue().get(environment, templateService);
             processorFactories.put(entry.getKey(), processorFactory);

qa/ingest-with-mustache/src/test/java/org/elasticsearch/plugin/ingest/AbstractMustacheTests.java

@@ -42,12 +42,12 @@ public abstract class AbstractMustacheTests extends ESTestCase {
             .build();
         MustacheScriptEngineService mustache = new MustacheScriptEngineService(settings);
         ScriptContextRegistry registry = new ScriptContextRegistry(
-            Collections.singletonList(InternalTemplateService.INGEST_SCRIPT_CONTEXT)
+            Collections.singletonList(MustacheTemplateService.INGEST_SCRIPT_CONTEXT)
         );
         ScriptService scriptService = new ScriptService(
             settings, new Environment(settings), Collections.singleton(mustache), null, registry
         );
-        templateService = new InternalTemplateService(scriptService);
+        templateService = new MustacheTemplateService(scriptService);
     }
 
 }