introduce clustering for query completion indices

pdb-api/src/main/java/org/lucares/pdb/api/DateTimeRange.java

@@ -15,8 +15,13 @@ public class DateTimeRange {
 		this.end = end;
 	}
 
+	public static DateTimeRange now() {
+		return relativeMillis(0);
+	}
+
 	public static DateTimeRange relative(final long amount, final TemporalUnit unit) {
-		return new DateTimeRange(OffsetDateTime.now().minus(amount, unit), OffsetDateTime.now());
+		final OffsetDateTime now = OffsetDateTime.now();
+		return new DateTimeRange(now.minus(amount, unit), now);
 	}
 
 	public static DateTimeRange relativeMillis(final long amount) {

pdb-api/src/main/java/org/lucares/pdb/api/QueryConstants.java

@@ -0,0 +1,5 @@
+package org.lucares.pdb.api;
+
+public interface QueryConstants {
+	String CARET_MARKER = "\ue001"; // character in the private use area
+}

pdb-api/src/main/java/org/lucares/pdb/api/QueryWithCaretMarker.java

@@ -0,0 +1,18 @@
+package org.lucares.pdb.api;
+
+public class QueryWithCaretMarker extends Query implements QueryConstants {
+
+	private final int caretIndex;
+
+	public QueryWithCaretMarker(final String query, final DateTimeRange dateRange, final int caretIndex) {
+		super(query, dateRange);
+		this.caretIndex = caretIndex;
+	}
+
+	public String getQueryWithCaretMarker() {
+		final StringBuilder queryBuilder = new StringBuilder(getQuery());
+		final StringBuilder queryWithCaretMarker = queryBuilder.insert(caretIndex, CARET_MARKER);
+		return queryWithCaretMarker.toString();
+	}
+
+}