1 files changed, 118 insertions, 0 deletions
diff --git a/impl_core/src/main/java/io/opencensus/implcore/stats/MetricUtils.java b/impl_core/src/main/java/io/opencensus/implcore/stats/MetricUtils.java
new file mode 100644
index 00000000..0dfb1d26
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+++ b/impl_core/src/main/java/io/opencensus/implcore/stats/MetricUtils.java
@@ -0,0 +1,118 @@
+/*
+ * Copyright 2018, OpenCensus Authors
+ *
+ * Licensed 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 io.opencensus.implcore.stats;
+
+import com.google.common.annotations.VisibleForTesting;
+import io.opencensus.common.Function;
+import io.opencensus.common.Functions;
+import io.opencensus.metrics.LabelKey;
+import io.opencensus.metrics.LabelValue;
+import io.opencensus.metrics.export.MetricDescriptor;
+import io.opencensus.metrics.export.MetricDescriptor.Type;
+import io.opencensus.stats.Aggregation;
+import io.opencensus.stats.Measure;
+import io.opencensus.stats.View;
+import io.opencensus.tags.TagKey;
+import io.opencensus.tags.TagValue;
+import java.util.ArrayList;
+import java.util.List;
+
+/*>>>
+import org.checkerframework.checker.nullness.qual.Nullable;
+*/
+
+@SuppressWarnings("deprecation")
+// Utils to convert Stats data models to Metric data models.
+final class MetricUtils {
+
+  @javax.annotation.Nullable
+  static MetricDescriptor viewToMetricDescriptor(View view) {
+    if (view.getWindow() instanceof View.AggregationWindow.Interval) {
+      // Only creates Metric for cumulative stats.
+      return null;
+    }
+    List<LabelKey> labelKeys = new ArrayList<LabelKey>();
+    for (TagKey tagKey : view.getColumns()) {
+      // TODO: add description
+      labelKeys.add(LabelKey.create(tagKey.getName(), ""));
+    }
+    Measure measure = view.getMeasure();
+    return MetricDescriptor.create(
+        view.getName().asString(),
+        view.getDescription(),
+        measure.getUnit(),
+        getType(measure, view.getAggregation()),
+        labelKeys);
+  }
+
+  @VisibleForTesting
+  static Type getType(Measure measure, Aggregation aggregation) {
+    return aggregation.match(
+        Functions.returnConstant(
+            measure.match(
+                TYPE_CUMULATIVE_DOUBLE_FUNCTION, // Sum Double
+                TYPE_CUMULATIVE_INT64_FUNCTION, // Sum Int64
+                TYPE_UNRECOGNIZED_FUNCTION)),
+        TYPE_CUMULATIVE_INT64_FUNCTION, // Count
+        TYPE_CUMULATIVE_DISTRIBUTION_FUNCTION, // Distribution
+        Functions.returnConstant(
+            measure.match(
+                TYPE_GAUGE_DOUBLE_FUNCTION, // LastValue Double
+                TYPE_GAUGE_INT64_FUNCTION, // LastValue Long
+                TYPE_UNRECOGNIZED_FUNCTION)),
+        AGGREGATION_TYPE_DEFAULT_FUNCTION);
+  }
+
+  static List<LabelValue> tagValuesToLabelValues(List</*@Nullable*/ TagValue> tagValues) {
+    List<LabelValue> labelValues = new ArrayList<LabelValue>();
+    for (/*@Nullable*/ TagValue tagValue : tagValues) {
+      labelValues.add(LabelValue.create(tagValue == null ? null : tagValue.asString()));
+    }
+    return labelValues;
+  }
+
+  private static final Function<Object, Type> TYPE_CUMULATIVE_DOUBLE_FUNCTION =
+      Functions.returnConstant(Type.CUMULATIVE_DOUBLE);
+
+  private static final Function<Object, Type> TYPE_CUMULATIVE_INT64_FUNCTION =
+      Functions.returnConstant(Type.CUMULATIVE_INT64);
+
+  private static final Function<Object, Type> TYPE_CUMULATIVE_DISTRIBUTION_FUNCTION =
+      Functions.returnConstant(Type.CUMULATIVE_DISTRIBUTION);
+
+  private static final Function<Object, Type> TYPE_GAUGE_DOUBLE_FUNCTION =
+      Functions.returnConstant(Type.GAUGE_DOUBLE);
+
+  private static final Function<Object, Type> TYPE_GAUGE_INT64_FUNCTION =
+      Functions.returnConstant(Type.GAUGE_INT64);
+
+  private static final Function<Object, Type> TYPE_UNRECOGNIZED_FUNCTION =
+      Functions.<Type>throwAssertionError();
+
+  private static final Function<Aggregation, Type> AGGREGATION_TYPE_DEFAULT_FUNCTION =
+      new Function<Aggregation, Type>() {
+        @Override
+        public Type apply(Aggregation arg) {
+          if (arg instanceof Aggregation.Mean) {
+            return Type.CUMULATIVE_DOUBLE; // Mean
+          }
+          throw new AssertionError();
+        }
+      };
+
+  private MetricUtils() {}
+}