Terms Facet: Allow to provide `_index` as the field, resulting in facets on indices, closes #374.

modules/elasticsearch/src/main/java/org/elasticsearch/search/facets/terms/IndexNameFacetCollector.java

@@ -0,0 +1,59 @@
+/*
+ * Licensed to Elastic Search and Shay Banon under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership. Elastic Search licenses this
+ * file to you 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 org.elasticsearch.search.facets.terms;
+
+import org.apache.lucene.index.IndexReader;
+import org.elasticsearch.common.collect.Sets;
+import org.elasticsearch.search.facets.Facet;
+import org.elasticsearch.search.facets.support.AbstractFacetCollector;
+
+import java.io.IOException;
+
+/**
+ * @author kimchy (shay.banon)
+ */
+public class IndexNameFacetCollector extends AbstractFacetCollector {
+
+    private final String indexName;
+
+    private final InternalTermsFacet.ComparatorType comparatorType;
+
+    private final int size;
+
+    private int count = 0;
+
+    public IndexNameFacetCollector(String facetName, String indexName, TermsFacet.ComparatorType comparatorType, int size) {
+        super(facetName);
+        this.indexName = indexName;
+        this.comparatorType = comparatorType;
+        this.size = size;
+    }
+
+    @Override protected void doSetNextReader(IndexReader reader, int docBase) throws IOException {
+    }
+
+    @Override protected void doCollect(int doc) throws IOException {
+        count++;
+    }
+
+    @Override public Facet facet() {
+        return new InternalTermsFacet(facetName, "_index", comparatorType, size, Sets.newHashSet(new TermsFacet.Entry(indexName, count)));
+    }
+}

modules/elasticsearch/src/main/java/org/elasticsearch/search/facets/terms/TermsFacetCollectorParser.java

@@ -84,6 +84,11 @@ public class TermsFacetCollectorParser implements FacetCollectorParser {
                 }
             }
         }
+
+        if ("_index".equals(field)) {
+            return new IndexNameFacetCollector(facetName, context.shardTarget().index(), comparatorType, size);
+        }
+
         Pattern pattern = null;
         if (regex != null) {
             pattern = Regex.compile(regex, regexFlags);

modules/test/integration/src/test/java/org/elasticsearch/test/integration/search/facets/SimpleFacetsTests.java

@@ -120,6 +120,47 @@ public class SimpleFacetsTests extends AbstractNodesTests {
         assertThat(facet.entries().get(0).count(), equalTo(2));
     }
 
+    @Test public void testTermsIndexFacet() throws Exception {
+        try {
+            client.admin().indices().prepareDelete("test1").execute().actionGet();
+            client.admin().indices().prepareDelete("test2").execute().actionGet();
+        } catch (Exception e) {
+            // ignore
+        }
+        client.admin().indices().prepareCreate("test1").execute().actionGet();
+        client.admin().indices().prepareCreate("test2").execute().actionGet();
+        client.admin().cluster().prepareHealth().setWaitForGreenStatus().execute().actionGet();
+
+        client.prepareIndex("test1", "type1").setSource(jsonBuilder().startObject()
+                .field("stag", "111")
+                .endObject()).execute().actionGet();
+
+        client.prepareIndex("test1", "type1").setSource(jsonBuilder().startObject()
+                .field("stag", "111")
+                .endObject()).execute().actionGet();
+
+        client.prepareIndex("test2", "type1").setSource(jsonBuilder().startObject()
+                .field("stag", "111")
+                .endObject()).execute().actionGet();
+        client.admin().indices().prepareFlush().setRefresh(true).execute().actionGet();
+
+
+        SearchResponse searchResponse = client.prepareSearch()
+                .setSize(0)
+                .setQuery(matchAllQuery())
+                .addFacet(termsFacet("facet1").field("_index").size(10))
+                .execute().actionGet();
+
+
+        TermsFacet facet = searchResponse.facets().facet("facet1");
+        assertThat(facet.name(), equalTo("facet1"));
+        assertThat(facet.entries().size(), equalTo(2));
+        assertThat(facet.entries().get(0).term(), equalTo("test1"));
+        assertThat(facet.entries().get(0).count(), equalTo(2));
+        assertThat(facet.entries().get(1).term(), equalTo("test2"));
+        assertThat(facet.entries().get(1).count(), equalTo(1));
+    }
+
     @Test public void testFilterFacets() throws Exception {
         try {
             client.admin().indices().prepareDelete("test").execute().actionGet();