fetch available values for gallery via autocomplete method

We had a method that returned the values of a field
with respect to a query. That method was inefficient,
because it executed the query, fetched all Docs
and collected the values.
The autocomplete method we introduced a while back
can answer the same question but much more efficiently.

pdb-ui/src/main/java/org/lucares/pdbui/PdbController.java

@@ -11,12 +11,12 @@ import java.util.List;
 import java.util.Locale;
 import java.util.Map;
 import java.util.SortedSet;
+import java.util.TreeSet;
 import java.util.concurrent.TimeUnit;
 import java.util.concurrent.locks.ReentrantLock;
 
 import org.apache.commons.lang3.StringUtils;
 import org.lucares.pdb.api.DateTimeRange;
-import org.lucares.pdb.api.Query;
 import org.lucares.pdb.api.QueryWithCaretMarker;
 import org.lucares.pdb.datastore.Proposal;
 import org.lucares.pdb.plot.api.AxisScale;
@@ -252,9 +252,14 @@ public class PdbController implements HardcodedValues, PropertyKeys {
 	SortedSet<String> fields(@PathVariable(name = "fieldName") final String fieldName,
 			@RequestParam(name = "query") final String query) {
 
-		final DateTimeRange dateRange = DateTimeRange.max();
-		final Query q = new Query(query, dateRange);
-		final SortedSet<String> fields = db.getFieldsValues(q, fieldName);
+		final String q = String.format("(%s) and %s=", query, fieldName);
+		final int caretIndex = q.length() + 1; // the autocomplete methods needs a 1-based index
+
+		final AutocompleteResponse autocompleteResponse = this.autocomplete(q, caretIndex);
+		final List<AutocompleteProposal> proposals = autocompleteResponse.getProposals();
+
+		final SortedSet<String> fields = CollectionUtils.map(proposals, new TreeSet<>(),
+				AutocompleteProposal::getValue);
 
 		return fields;
 	}