1 files changed, 150 insertions, 0 deletions
diff --git a/api/src/main/java/io/opencensus/metrics/MetricDescriptor.java b/api/src/main/java/io/opencensus/metrics/MetricDescriptor.java
new file mode 100644
index 00000000..4558446a
--- /dev/null
+++ b/api/src/main/java/io/opencensus/metrics/MetricDescriptor.java
@@ -0,0 +1,150 @@
+/*
+ * 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.metrics;
+
+import com.google.auto.value.AutoValue;
+import io.opencensus.common.ExperimentalApi;
+import io.opencensus.internal.Utils;
+import java.util.ArrayList;
+import java.util.Collections;
+import java.util.List;
+import javax.annotation.concurrent.Immutable;
+
+/**
+ * {@link MetricDescriptor} defines a {@code Metric} type and its schema.
+ *
+ * @since 0.16
+ */
+@ExperimentalApi
+@Immutable
+@AutoValue
+public abstract class MetricDescriptor {
+
+  MetricDescriptor() {}
+
+  /**
+   * Creates a {@link MetricDescriptor}.
+   *
+   * @param name name of {@code MetricDescriptor}.
+   * @param description description of {@code MetricDescriptor}.
+   * @param unit the metric unit.
+   * @param type type of {@code MetricDescriptor}.
+   * @param labelKeys the label keys associated with the {@code MetricDescriptor}.
+   * @return a {@code MetricDescriptor}.
+   * @since 0.16
+   */
+  public static MetricDescriptor create(
+      String name, String description, String unit, Type type, List<LabelKey> labelKeys) {
+    Utils.checkNotNull(labelKeys, "labelKeys");
+    Utils.checkListElementNotNull(labelKeys, "labelKey");
+    return new AutoValue_MetricDescriptor(
+        name,
+        description,
+        unit,
+        type,
+        Collections.unmodifiableList(new ArrayList<LabelKey>(labelKeys)));
+  }
+
+  /**
+   * Returns the metric descriptor name.
+   *
+   * @return the metric descriptor name.
+   * @since 0.16
+   */
+  public abstract String getName();
+
+  /**
+   * Returns the description of this metric descriptor.
+   *
+   * @return the description of this metric descriptor.
+   * @since 0.16
+   */
+  public abstract String getDescription();
+
+  /**
+   * Returns the unit of this metric descriptor.
+   *
+   * @return the unit of this metric descriptor.
+   * @since 0.16
+   */
+  public abstract String getUnit();
+
+  /**
+   * Returns the type of this metric descriptor.
+   *
+   * @return the type of this metric descriptor.
+   * @since 0.16
+   */
+  public abstract Type getType();
+
+  /**
+   * Returns the label keys associated with this metric descriptor.
+   *
+   * @return the label keys associated with this metric descriptor.
+   * @since 0.16
+   */
+  public abstract List<LabelKey> getLabelKeys();
+
+  /**
+   * The kind of metric. It describes how the data is reported.
+   *
+   * <p>A gauge is an instantaneous measurement of a value.
+   *
+   * <p>A cumulative measurement is a value accumulated over a time interval. In a time series,
+   * cumulative measurements should have the same start time and increasing end times, until an
+   * event resets the cumulative value to zero and sets a new start time for the following points.
+   *
+   * @since 0.16
+   */
+  public enum Type {
+
+    /**
+     * An instantaneous measurement of an int64 value.
+     *
+     * @since 0.16
+     */
+    GAUGE_INT64,
+
+    /**
+     * An instantaneous measurement of a double value.
+     *
+     * @since 0.16
+     */
+    GAUGE_DOUBLE,
+
+    /**
+     * An cumulative measurement of an int64 value.
+     *
+     * @since 0.16
+     */
+    CUMULATIVE_INT64,
+
+    /**
+     * An cumulative measurement of a double value.
+     *
+     * @since 0.16
+     */
+    CUMULATIVE_DOUBLE,
+
+    /**
+     * An cumulative measurement of a distribution value.
+     *
+     * @since 0.16
+     */
+    CUMULATIVE_DISTRIBUTION,
+  }
+}