Add search engine and quick search for repositories (#1727)

Add a powerful search engine based on lucene to the scm-manager api.
The api can be used to index objects, simply by annotating them and add them to an index.
The first indexed object is the repository which could queried by quick search in the header.

scm-webapp/src/main/java/sonia/scm/search/DefaultIndexQueue.java

@@ -0,0 +1,77 @@
+/*
+ * MIT License
+ *
+ * Copyright (c) 2020-present Cloudogu GmbH and Contributors
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in all
+ * copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+ * SOFTWARE.
+ */
+
+package sonia.scm.search;
+
+import com.google.common.annotations.VisibleForTesting;
+
+import javax.inject.Inject;
+import javax.inject.Singleton;
+import java.io.Closeable;
+import java.io.IOException;
+import java.util.concurrent.ExecutorService;
+import java.util.concurrent.Executors;
+import java.util.concurrent.atomic.AtomicLong;
+
+@Singleton
+public class DefaultIndexQueue implements IndexQueue, Closeable {
+
+  private final ExecutorService executor = Executors.newSingleThreadExecutor();
+
+  private final AtomicLong size = new AtomicLong(0);
+
+  private final SearchEngine searchEngine;
+
+  @Inject
+  public DefaultIndexQueue(SearchEngine searchEngine) {
+    this.searchEngine = searchEngine;
+  }
+
+  @Override
+  public Index getQueuedIndex(String name, IndexOptions indexOptions) {
+    return new QueuedIndex(this, name, indexOptions);
+  }
+
+  public SearchEngine getSearchEngine() {
+    return searchEngine;
+  }
+
+  void enqueue(IndexQueueTaskWrapper task) {
+    size.incrementAndGet();
+    executor.execute(() -> {
+      task.run();
+      size.decrementAndGet();
+    });
+  }
+
+  @VisibleForTesting
+  long getSize() {
+    return size.get();
+  }
+
+  @Override
+  public void close() throws IOException {
+    executor.shutdown();
+  }
+}