Merge pull request #603 from iRevive/sdk-metrics/aggregation-temporal…

…ity-selector

sdk-metrics: add `AggregationTemporalitySelector` [no ci]

sdk/metrics/src/main/scala/org/typelevel/otel4s/sdk/metrics/exporter/AggregationTemporalitySelector.scala

@@ -0,0 +1,72 @@
+/*
+ * Copyright 2024 Typelevel
+ *
+ * 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 org.typelevel.otel4s.sdk.metrics.exporter
+
+import org.typelevel.otel4s.sdk.metrics.InstrumentType
+import org.typelevel.otel4s.sdk.metrics.data.AggregationTemporality
+
+/** Used by the `MetricReader` to decide the default aggregation temporality.
+  */
+trait AggregationTemporalitySelector {
+
+  /** Returns preferred aggregation temporality for the given
+    * [[InstrumentType]].
+    */
+  def select(instrumentType: InstrumentType): AggregationTemporality
+}
+
+object AggregationTemporalitySelector {
+
+  /** Returns cumulative aggregation temporality for all instruments.
+    */
+  def alwaysCumulative: AggregationTemporalitySelector =
+    _ => AggregationTemporality.Cumulative
+
+  /** Returns cumulative aggregation temporality for `UpDownCounter` and
+    * `ObservableUpDownCounter`, and delta aggregation temporality for any other
+    * instrument.
+    */
+  def deltaPreferred: AggregationTemporalitySelector = {
+    case InstrumentType.UpDownCounter =>
+      AggregationTemporality.Cumulative
+
+    case InstrumentType.ObservableUpDownCounter =>
+      AggregationTemporality.Cumulative
+
+    case _ =>
+      AggregationTemporality.Delta
+  }
+
+  /** Returns cumulative aggregation temporality for `UpDownCounter`,
+    * `ObservableUpDownCounter`, `ObservableCounter`, and delta aggregation
+    * temporality for any other instrument.
+    */
+  def lowMemory: AggregationTemporalitySelector = {
+    case InstrumentType.UpDownCounter =>
+      AggregationTemporality.Cumulative
+
+    case InstrumentType.ObservableUpDownCounter =>
+      AggregationTemporality.Cumulative
+
+    case InstrumentType.ObservableCounter =>
+      AggregationTemporality.Cumulative
+
+    case _ =>
+      AggregationTemporality.Delta
+  }
+
+}

sdk/metrics/src/test/scala/org/typelevel/otel4s/sdk/metrics/exporter/AggregationTemporalitySelectorSuite.scala

@@ -0,0 +1,66 @@
+/*
+ * Copyright 2024 Typelevel
+ *
+ * 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 org.typelevel.otel4s.sdk.metrics.exporter
+
+import munit.FunSuite
+import org.typelevel.otel4s.sdk.metrics.InstrumentType
+import org.typelevel.otel4s.sdk.metrics.data.AggregationTemporality
+
+class AggregationTemporalitySelectorSuite extends FunSuite {
+
+  test("always cumulative") {
+    val selector = AggregationTemporalitySelector.alwaysCumulative
+    InstrumentType.values.foreach { tpe =>
+      assertEquals(selector.select(tpe), AggregationTemporality.Cumulative)
+    }
+  }
+
+  test("delta preferred") {
+    val selector = AggregationTemporalitySelector.deltaPreferred
+    InstrumentType.values.foreach { tpe =>
+      val expected = tpe match {
+        case InstrumentType.UpDownCounter =>
+          AggregationTemporality.Cumulative
+        case InstrumentType.ObservableUpDownCounter =>
+          AggregationTemporality.Cumulative
+        case _ =>
+          AggregationTemporality.Delta
+      }
+
+      assertEquals(selector.select(tpe), expected)
+    }
+  }
+
+  test("low memory") {
+    val selector = AggregationTemporalitySelector.lowMemory
+    InstrumentType.values.foreach { tpe =>
+      val expected = tpe match {
+        case InstrumentType.UpDownCounter =>
+          AggregationTemporality.Cumulative
+        case InstrumentType.ObservableUpDownCounter =>
+          AggregationTemporality.Cumulative
+        case InstrumentType.ObservableCounter =>
+          AggregationTemporality.Cumulative
+        case _ =>
+          AggregationTemporality.Delta
+      }
+
+      assertEquals(selector.select(tpe), expected)
+    }
+  }
+
+}