Add Aggregation.LastValue and AggregationData.LastValueData to support Gauge (#1055)

* Add LastValue and LastValueData

* Support LastValue and LastValueData in impl

* Use Utils instead of Precondition

* Add LastValue and remove Mean from match() method.

* Support LastValue and LastValueData in exporters and zpages.

* Update MutableLastValue, add comments on why Mean is still supported.

3 files changed, 52 insertions, 37 deletions

diff --git a/api/src/test/java/io/opencensus/stats/AggregationDataTest.java b/api/src/test/java/io/opencensus/stats/AggregationDataTest.java
index 3431d043..9f2aa589 100644
--- a/api/src/test/java/io/opencensus/stats/AggregationDataTest.java
+++ b/api/src/test/java/io/opencensus/stats/AggregationDataTest.java
@@ -23,6 +23,8 @@ import io.opencensus.common.Function;
 import io.opencensus.common.Functions;
 import io.opencensus.stats.AggregationData.CountData;
 import io.opencensus.stats.AggregationData.DistributionData;
+import io.opencensus.stats.AggregationData.LastValueDataDouble;
+import io.opencensus.stats.AggregationData.LastValueDataLong;
 import io.opencensus.stats.AggregationData.MeanData;
 import io.opencensus.stats.AggregationData.SumDataDouble;
 import io.opencensus.stats.AggregationData.SumDataLong;
@@ -95,6 +97,8 @@ public class AggregationDataTest {
         .addEqualityGroup(DistributionData.create(10, 10, 1, 1, 55.5, Arrays.asList(0L, 10L, 0L)))
         .addEqualityGroup(MeanData.create(5.0, 1), MeanData.create(5.0, 1))
         .addEqualityGroup(MeanData.create(-5.0, 1), MeanData.create(-5.0, 1))
+        .addEqualityGroup(LastValueDataDouble.create(20.0), LastValueDataDouble.create(20.0))
+        .addEqualityGroup(LastValueDataLong.create(20), LastValueDataLong.create(20))
         .testEquals();
   }
 
@@ -105,8 +109,9 @@ public class AggregationDataTest {
             SumDataDouble.create(10.0),
             SumDataLong.create(100000000),
             CountData.create(40),
-            MeanData.create(5.0, 1),
-            DistributionData.create(1, 1, 1, 1, 0, Arrays.asList(0L, 10L, 0L)));
+            DistributionData.create(1, 1, 1, 1, 0, Arrays.asList(0L, 10L, 0L)),
+            LastValueDataDouble.create(20.0),
+            LastValueDataLong.create(200000000L));
 
     final List<Object> actual = new ArrayList<Object>();
     for (AggregationData aggregation : aggregations) {
@@ -132,17 +137,24 @@ public class AggregationDataTest {
               return null;
             }
           },
-          new Function<MeanData, Void>() {
+          new Function<DistributionData, Void>() {
             @Override
-            public Void apply(MeanData arg) {
-              actual.add(arg.getMean());
+            public Void apply(DistributionData arg) {
+              actual.add(arg.getBucketCounts());
               return null;
             }
           },
-          new Function<DistributionData, Void>() {
+          new Function<LastValueDataDouble, Void>() {
             @Override
-            public Void apply(DistributionData arg) {
-              actual.add(arg.getBucketCounts());
+            public Void apply(LastValueDataDouble arg) {
+              actual.add(arg.getLastValue());
+              return null;
+            }
+          },
+          new Function<LastValueDataLong, Void>() {
+            @Override
+            public Void apply(LastValueDataLong arg) {
+              actual.add(arg.getLastValue());
               return null;
             }
           },
@@ -150,6 +162,7 @@ public class AggregationDataTest {
     }
 
     assertThat(actual)
-        .isEqualTo(Arrays.asList(10.0, 100000000L, 40L, 5.0, Arrays.asList(0L, 10L, 0L)));
+        .containsExactly(10.0, 100000000L, 40L, Arrays.asList(0L, 10L, 0L), 20.0, 200000000L)
+        .inOrder();
   }
 }
diff --git a/api/src/test/java/io/opencensus/stats/AggregationTest.java b/api/src/test/java/io/opencensus/stats/AggregationTest.java
index 3ef131b8..c2e6a716 100644
--- a/api/src/test/java/io/opencensus/stats/AggregationTest.java
+++ b/api/src/test/java/io/opencensus/stats/AggregationTest.java
@@ -19,10 +19,10 @@ package io.opencensus.stats;
 import static com.google.common.truth.Truth.assertThat;
 
 import com.google.common.testing.EqualsTester;
-import io.opencensus.common.Function;
 import io.opencensus.common.Functions;
 import io.opencensus.stats.Aggregation.Count;
 import io.opencensus.stats.Aggregation.Distribution;
+import io.opencensus.stats.Aggregation.LastValue;
 import io.opencensus.stats.Aggregation.Mean;
 import io.opencensus.stats.Aggregation.Sum;
 import java.util.ArrayList;
@@ -66,6 +66,7 @@ public class AggregationTest {
             Distribution.create(BucketBoundaries.create(Arrays.asList(0.0, 1.0, 5.0))),
             Distribution.create(BucketBoundaries.create(Arrays.asList(0.0, 1.0, 5.0))))
         .addEqualityGroup(Mean.create(), Mean.create())
+        .addEqualityGroup(LastValue.create(), LastValue.create())
         .testEquals();
   }
 
@@ -76,39 +77,21 @@ public class AggregationTest {
             Sum.create(),
             Count.create(),
             Mean.create(),
-            Distribution.create(BucketBoundaries.create(Arrays.asList(-10.0, 1.0, 5.0))));
+            Distribution.create(BucketBoundaries.create(Arrays.asList(-10.0, 1.0, 5.0))),
+            LastValue.create());
 
     List<String> actual = new ArrayList<String>();
     for (Aggregation aggregation : aggregations) {
       actual.add(
           aggregation.match(
-              new Function<Sum, String>() {
-                @Override
-                public String apply(Sum arg) {
-                  return "SUM";
-                }
-              },
-              new Function<Count, String>() {
-                @Override
-                public String apply(Count arg) {
-                  return "COUNT";
-                }
-              },
-              new Function<Mean, String>() {
-                @Override
-                public String apply(Mean arg) {
-                  return "MEAN";
-                }
-              },
-              new Function<Distribution, String>() {
-                @Override
-                public String apply(Distribution arg) {
-                  return "DISTRIBUTION";
-                }
-              },
-              Functions.<String>throwIllegalArgumentException()));
+              Functions.returnConstant("SUM"),
+              Functions.returnConstant("COUNT"),
+              Functions.returnConstant("DISTRIBUTION"),
+              Functions.returnConstant("LASTVALUE"),
+              Functions.returnConstant("UNKNOWN")));
     }
 
-    assertThat(actual).isEqualTo(Arrays.asList("SUM", "COUNT", "MEAN", "DISTRIBUTION"));
+    assertThat(actual)
+        .isEqualTo(Arrays.asList("SUM", "COUNT", "UNKNOWN", "DISTRIBUTION", "LASTVALUE"));
   }
 }
diff --git a/api/src/test/java/io/opencensus/stats/ViewDataTest.java b/api/src/test/java/io/opencensus/stats/ViewDataTest.java
index 0dc78e33..89009f34 100644
--- a/api/src/test/java/io/opencensus/stats/ViewDataTest.java
+++ b/api/src/test/java/io/opencensus/stats/ViewDataTest.java
@@ -27,10 +27,13 @@ import io.opencensus.common.Functions;
 import io.opencensus.common.Timestamp;
 import io.opencensus.stats.Aggregation.Count;
 import io.opencensus.stats.Aggregation.Distribution;
+import io.opencensus.stats.Aggregation.LastValue;
 import io.opencensus.stats.Aggregation.Mean;
 import io.opencensus.stats.Aggregation.Sum;
 import io.opencensus.stats.AggregationData.CountData;
 import io.opencensus.stats.AggregationData.DistributionData;
+import io.opencensus.stats.AggregationData.LastValueDataDouble;
+import io.opencensus.stats.AggregationData.LastValueDataLong;
 import io.opencensus.stats.AggregationData.SumDataDouble;
 import io.opencensus.stats.AggregationData.SumDataLong;
 import io.opencensus.stats.View.AggregationWindow;
@@ -218,6 +221,22 @@ public final class ViewDataTest {
             CountData.create(100)));
   }
 
+  @Test
+  public void preventAggregationAndAggregationDataMismatch_LastValueDouble_LastValueLong() {
+    aggregationAndAggregationDataMismatch(
+        createView(LastValue.create(), MEASURE_DOUBLE),
+        ImmutableMap.<List<TagValue>, AggregationData>of(
+            Arrays.asList(V1, V2), LastValueDataLong.create(100)));
+  }
+
+  @Test
+  public void preventAggregationAndAggregationDataMismatch_LastValueLong_LastValueDouble() {
+    aggregationAndAggregationDataMismatch(
+        createView(LastValue.create(), MEASURE_LONG),
+        ImmutableMap.<List<TagValue>, AggregationData>of(
+            Arrays.asList(V1, V2), LastValueDataDouble.create(100)));
+  }
+
   private static View createView(Aggregation aggregation) {
     return createView(aggregation, MEASURE_DOUBLE);
   }