Split regular histograms from date histograms.

core/src/main/java/org/elasticsearch/common/rounding/Rounding.java

@@ -35,24 +35,9 @@ public abstract class Rounding implements Streamable {
     public abstract byte id();
 
     /**
-     * Given a value, compute a key that uniquely identifies the rounded value although it is not necessarily equal to the rounding value itself.
+     * Rounds the given value.
      */
-    public abstract long roundKey(long value);
-
-    /**
-     * Compute the rounded value given the key that identifies it.
-     */
-    public abstract long valueForKey(long key);
-
-    /**
-     * Rounds the given value, equivalent to calling <code>roundValue(roundKey(value))</code>.
-     *
-     * @param value The value to round.
-     * @return      The rounded value.
-     */
-    public final long round(long value) {
-        return valueForKey(roundKey(value));
-    }
+    public abstract long round(long value);
 
     /**
      * Given the rounded value (which was potentially generated by {@link #round(long)}, returns the next rounding value. For example, with
@@ -112,13 +97,8 @@ public static long roundValue(long key, long interval) {
         }
 
         @Override
-        public long roundKey(long value) {
-            return roundKey(value, interval);
-        }
-
-        @Override
-        public long valueForKey(long key) {
-            return key * interval;
+        public long round(long value) {
+            return roundKey(value, interval) * interval;
         }
 
         @Override
@@ -179,13 +159,8 @@ public byte id() {
         }
 
         @Override
-        public long roundKey(long utcMillis) {
-            return rounding.roundKey((long) (factor * utcMillis));
-        }
-
-        @Override
-        public long valueForKey(long key) {
-            return rounding.valueForKey(key);
+        public long round(long utcMillis) {
+            return rounding.round((long) (factor * utcMillis));
         }
 
         @Override
@@ -248,13 +223,8 @@ public byte id() {
         }
 
         @Override
-        public long roundKey(long value) {
-            return rounding.roundKey(value - offset);
-        }
-
-        @Override
-        public long valueForKey(long key) {
-            return offset + rounding.valueForKey(key);
+        public long round(long value) {
+            return rounding.round(value - offset) + offset;
         }
 
         @Override

core/src/main/java/org/elasticsearch/common/rounding/TimeZoneRounding.java

@@ -31,6 +31,9 @@
 import java.util.Objects;
 
 /**
+ * A rounding strategy for dates. It is typically used to group together dates
+ * that are part of the same hour/day/month, taking into account time zones and
+ * daylight saving times.
  */
 public abstract class TimeZoneRounding extends Rounding {
     public static final ParseField INTERVAL_FIELD = new ParseField("interval");
@@ -125,7 +128,7 @@ public byte id() {
         }
 
         @Override
-        public long roundKey(long utcMillis) {
+        public long round(long utcMillis) {
             long rounded = field.roundFloor(utcMillis);
             if (timeZone.isFixed() == false && timeZone.getOffset(utcMillis) != timeZone.getOffset(rounded)) {
                 // in this case, we crossed a time zone transition. In some edge cases this will
@@ -138,20 +141,14 @@ public long roundKey(long utcMillis) {
             return rounded;
         }
 
-        @Override
-        public long valueForKey(long time) {
-            assert roundKey(time) == time;
-            return time;
-        }
-
         @Override
         public long nextRoundingValue(long utcMillis) {
-            long floor = roundKey(utcMillis);
+            long floor = round(utcMillis);
             // add one unit and round to get to next rounded value
-            long next = roundKey(field.add(floor, 1));
+            long next = round(field.add(floor, 1));
             if (next == floor) {
                 // in rare case we need to add more than one unit
-                next = roundKey(field.add(floor, 2));
+                next = round(field.add(floor, 2));
             }
             return next;
         }
@@ -216,7 +213,7 @@ public byte id() {
         }
 
         @Override
-        public long roundKey(long utcMillis) {
+        public long round(long utcMillis) {
             long timeLocal = timeZone.convertUTCToLocal(utcMillis);
             long rounded = Rounding.Interval.roundValue(Rounding.Interval.roundKey(timeLocal, interval), interval);
             long roundedUTC;
@@ -225,7 +222,7 @@ public long roundKey(long utcMillis) {
                 // check if we crossed DST transition, in this case we want the last rounded value before the transition
                 long transition = timeZone.previousTransition(utcMillis);
                 if (transition != utcMillis && transition > roundedUTC) {
-                    roundedUTC = roundKey(transition - 1);
+                    roundedUTC = round(transition - 1);
                 }
             } else {
                 /*
@@ -276,12 +273,6 @@ private boolean isInDSTGap(long instantLocal) {
             return false;
         }
 
-        @Override
-        public long valueForKey(long time) {
-            assert roundKey(time) == time;
-            return time;
-        }
-
         @Override
         public long nextRoundingValue(long time) {
             long timeLocal = time;

core/src/main/java/org/elasticsearch/search/SearchModule.java

@@ -116,6 +116,7 @@
 import org.elasticsearch.search.aggregations.bucket.histogram.DateHistogramParser;
 import org.elasticsearch.search.aggregations.bucket.histogram.HistogramAggregationBuilder;
 import org.elasticsearch.search.aggregations.bucket.histogram.HistogramParser;
+import org.elasticsearch.search.aggregations.bucket.histogram.InternalDateHistogram;
 import org.elasticsearch.search.aggregations.bucket.histogram.InternalHistogram;
 import org.elasticsearch.search.aggregations.bucket.missing.InternalMissing;
 import org.elasticsearch.search.aggregations.bucket.missing.MissingAggregationBuilder;
@@ -546,7 +547,7 @@ private void registerBuiltinAggregations() {
         registerAggregation(new AggregationSpec(HistogramAggregationBuilder::new, new HistogramParser(),
                 HistogramAggregationBuilder.AGGREGATION_NAME_FIELD).addResultReader(InternalHistogram::new));
         registerAggregation(new AggregationSpec(DateHistogramAggregationBuilder::new, new DateHistogramParser(),
-                DateHistogramAggregationBuilder.AGGREGATION_NAME_FIELD));
+                DateHistogramAggregationBuilder.AGGREGATION_NAME_FIELD).addResultReader(InternalDateHistogram::new));
         registerAggregation(new AggregationSpec(GeoDistanceAggregationBuilder::new, new GeoDistanceParser(),
                 GeoDistanceAggregationBuilder.AGGREGATION_NAME_FIELD).addResultReader(InternalGeoDistance::new));
         registerAggregation(new AggregationSpec(GeoGridAggregationBuilder::new, new GeoHashGridParser(),