[NAE-2090] add documentation

Author: tuplle

application-engine/src/main/groovy/com/netgrif/application/engine/integration/modules/ModuleHolder.groovy

@@ -2,6 +2,6 @@ package com.netgrif.application.engine.integration.modules
 
 /**
  * A class where the module services are injected. The plugins are injected into metaclasses
- * */
+ */
 class ModuleHolder {
 }

application-engine/src/main/groovy/com/netgrif/application/engine/integration/modules/ModuleServiceHolder.groovy

@@ -1,4 +1,7 @@
 package com.netgrif.application.engine.integration.modules
 
+/**
+ * A class where the module services are injected for a named module. The plugins are injected into metaclasses
+ */
 class ModuleServiceHolder {
 }

application-engine/src/main/groovy/com/netgrif/application/engine/integration/modules/ModuleServiceInjector.groovy

@@ -9,6 +9,16 @@ import org.springframework.boot.ApplicationArguments
 import org.springframework.boot.autoconfigure.condition.ConditionalOnProperty
 import org.springframework.stereotype.Component
 
+/**
+ * Component responsible for injecting module services into the application runtime.
+ * This class implements {@link ApplicationEngineFinishRunner} to perform the injection
+ * after the application finishes its startup routine. The services are grouped by modules
+ * and made available for runtime action delegation.
+ *
+ * The execution of this class is controlled by properties defined in the application configuration.
+ * By default, it is enabled and executed in the specified order.
+ */
+
 @Component
 @RunnerOrder(209)
 @ConditionalOnProperty(value = "nae.modules.services.enabled", havingValue = "true", matchIfMissing = true)
@@ -17,6 +27,16 @@ class ModuleServiceInjector implements ApplicationEngineFinishRunner {
     private static final Logger log = LoggerFactory.getLogger(ModuleServiceInjector.class)
     private final String DEFAULT_KEY = "default"
 
+    /**
+     * Executes the injection of services annotated with {@code @ModuleService}.
+     * This method collects all beans marked with the {@code @ModuleService} annotation,
+     * groups them by their associated module, and injects them into the respective meta-classes
+     * (e.g., {@code ModuleHolder} and {@code ModuleServiceHolder}).
+     *
+     * @param args application arguments passed during startup
+     * @throws Exception if any error occurs during the injection process
+     */
+
     @Override
     void run(ApplicationArguments args) throws Exception {
         def injectableBeans = ApplicationContextProvider.getAppContext().getBeansWithAnnotation(ModuleService.class)
@@ -41,6 +61,17 @@ class ModuleServiceInjector implements ApplicationEngineFinishRunner {
         }
     }
 
+    /**
+     * Groups services annotated with {@code @ModuleService} by their associated module.
+     * Each service is categorized under a module key specified by the annotation's value.
+     * Services without a specified module are grouped under the "default" key.
+     *
+     * @param services a map of service names to service instances retrieved from the application context
+     * @return a map where each key represents a module, and the value is another map containing
+     *         services (name and instance) associated with that module
+     * @throws IllegalStateException if any service lacks the {@code @ModuleService} annotation
+     */
+
     private Map<String, Map<String, Object>> groupServicesByModule(Map<String, Object> services) {
         Map<String, Map<String, Object>> grouped = [(DEFAULT_KEY): [:]]
         services.each { entry ->