Add some documentation

src/main/kotlin/helpers/ElasticSearchWrapper.kt

@@ -4,6 +4,7 @@ import java.util.Properties
 import org.apache.http.HttpHost
 import org.apache.logging.log4j.LogManager
 import org.elasticsearch.ElasticsearchException
+import org.elasticsearch.action.admin.indices.alias.get.GetAliasesRequest
 import org.elasticsearch.client.RequestOptions
 import org.elasticsearch.client.RestClient
 import org.elasticsearch.client.RestHighLevelClient
@@ -11,14 +12,32 @@ import org.elasticsearch.client.core.CountRequest
 import org.elasticsearch.client.indices.GetIndexRequest
 import org.elasticsearch.index.query.QueryBuilders
 
+/**
+ * This class facilitates a connection to the Elasticsearch cluster and offers convenience functions to retrieve
+ * the necessary data.
+ */
 class ElasticSearchWrapper(settings: Properties) {
     private val log = LogManager.getLogger("ElasticSearchWrapper")
     private val host = settings.getProperty(KEYS.SettingsProps.elasticHost)
     private val port = settings.getProperty(KEYS.SettingsProps.elasticPort).toInt()
-
     private val documentsIndex = settings.getProperty(KEYS.SettingsProps.elasticIndex)
     private val client = connect()
 
+    /**
+     * Establishes a connection to the client and ensures, that the index is present. The index may be an alias
+     * or an index directly.
+     *
+     * If the connection fails or the index does not exists, no client is created. When this happens all
+     * functions will be returning default values instead of executing the query.
+     *
+     * The service needs to be restarted to establish a new connection. It is reported within the logs that
+     * there is no successful connection.
+     *
+     * This makes it easier to test this service, and ensures that it keeps running even if elasticsearch is not
+     * available.
+     *
+     * TODO: In the future find a better solution.
+     */
     private fun connect(): RestHighLevelClient? {
         return try {
             val c = RestHighLevelClient(
@@ -26,8 +45,10 @@ class ElasticSearchWrapper(settings: Properties) {
                             HttpHost(host, port)
                     ))
 
-            if (!c.indices().exists(GetIndexRequest(documentsIndex), RequestOptions.DEFAULT)) {
-                log.error("Could not find the index defined in the configuration: $documentsIndex.")
+
+            if (!c.indices().exists(GetIndexRequest(documentsIndex), RequestOptions.DEFAULT) ||
+                    !c.indices().existsAlias(GetAliasesRequest(documentsIndex), RequestOptions.DEFAULT)) {
+                log.error("Could not find the index or alias defined in the configuration: $documentsIndex.")
                 null
             } else {
                 log.info("Successfully connected to index $documentsIndex. Ready to query.")
@@ -39,6 +60,9 @@ class ElasticSearchWrapper(settings: Properties) {
         }
     }
 
+    /**
+     * Counts the number of documents attached to a specific record set.
+     */
     fun countNumberOfDocuments(recordSetIdentifier: String): Int {
         return client.let {
             if (it == null) {