From e07a3bb2002c37a8b2d604162387fb45dcd03b6e Mon Sep 17 00:00:00 2001
From: Hugh Simpson <hsimpson@rzsoftware.com>
Date: Fri, 4 Aug 2023 13:44:38 +0100
Subject: [PATCH] initial implementation of actual conversion

---
 .../scala/kamon/otel/MetricsConverter.scala   | 87 ++++++++++++++++++-
 1 file changed, 83 insertions(+), 4 deletions(-)

diff --git a/reporters/kamon-opentelemetry/src/main/scala/kamon/otel/MetricsConverter.scala b/reporters/kamon-opentelemetry/src/main/scala/kamon/otel/MetricsConverter.scala
index 20c02f951..d21afc6ac 100644
--- a/reporters/kamon-opentelemetry/src/main/scala/kamon/otel/MetricsConverter.scala
+++ b/reporters/kamon-opentelemetry/src/main/scala/kamon/otel/MetricsConverter.scala
@@ -15,16 +15,95 @@
  */
 package kamon.otel
 
-import io.opentelemetry.sdk.metrics.data.MetricData
+import io.opentelemetry.sdk.common.InstrumentationScopeInfo
+import io.opentelemetry.sdk.metrics.data._
+import io.opentelemetry.sdk.metrics.internal.data._
 import io.opentelemetry.sdk.resources.Resource
-import kamon.metric.PeriodSnapshot
+import kamon.metric.Instrument.Snapshot
+import kamon.metric.{Distribution, MeasurementUnit, MetricSnapshot, PeriodSnapshot}
+import kamon.tag.Lookups
+import kamon.trace.Span.TagKeys
 
+import java.lang.{Double => JDouble, Long => JLong}
+import java.time.Instant
 import java.util.{Collection => JCollection}
+import scala.collection.JavaConverters._
+
+class WithResourceMetricsConverter(resource: Resource, kamonVersion: String, from: Instant, to: Instant) {
+  private val fromNs = from.toEpochMilli * 1000000
+  private val toNs = to.toEpochMilli * 1000000
+
+  private def instrumentationScopeInfo(snapshot: MetricSnapshot[_, _]): InstrumentationScopeInfo = {
+    // logic for looking up the component doesn't really seem to make sense - to be compliant we should probably be grouping the metrics by component before calling this
+    InstrumentationScopeInfo.create(snapshot.instruments.headOption.flatMap(_.tags.get(Lookups.option(TagKeys.Component))) getOrElse "kamon-instrumentation", kamonVersion, null)
+  }
+
+  private def toString(unit: MeasurementUnit): String = unit.magnitude.name
+
+  def toGaugeDatum(g: Snapshot[Double]): DoublePointData = ImmutableDoublePointData.create(fromNs, toNs, SpanConverter.toAttributes(g.tags), g.value)
+
+  def toGaugeData(g: Seq[Snapshot[Double]]): GaugeData[DoublePointData] = ImmutableGaugeData.create(g.map(toGaugeDatum).asJava)
+
+  def convertGauge(gauge: MetricSnapshot.Values[Double]): MetricData =
+    ImmutableMetricData.createDoubleGauge(
+      resource,
+      instrumentationScopeInfo(gauge),
+      gauge.name,
+      gauge.description,
+      toString(gauge.settings.unit),
+      toGaugeData(gauge.instruments))
+
+  def toHistogramDatum(s: Snapshot[Distribution]): HistogramPointData =
+    ImmutableHistogramPointData.create(
+      fromNs,
+      toNs,
+      SpanConverter.toAttributes(s.tags),
+      JDouble valueOf s.value.sum.toDouble,
+      JDouble valueOf s.value.min.toDouble,
+      JDouble valueOf s.value.max.toDouble,
+      s.value.buckets.map(JDouble valueOf _.value.toDouble).asJava,
+      s.value.buckets.map(JLong valueOf _.frequency).asJava
+    )
+
+  def toHistogramData(any: Seq[Snapshot[Distribution]]): HistogramData =
+    ImmutableHistogramData.create(AggregationTemporality.CUMULATIVE, any.map(toHistogramDatum).asJava)
+
+  def convertHistogram(histogram: MetricSnapshot.Distributions): MetricData =
+    ImmutableMetricData.createDoubleHistogram(
+      resource,
+      instrumentationScopeInfo(histogram),
+      histogram.name,
+      histogram.description,
+      toString(histogram.settings.unit),
+      toHistogramData(histogram.instruments))
+
+  def toCounterDatum(g: Snapshot[Long]): LongPointData =
+    ImmutableLongPointData.create(fromNs, toNs, SpanConverter.toAttributes(g.tags), g.value)
+
+  def toCounterData(g: Seq[Snapshot[Long]]): SumData[LongPointData] =
+    ImmutableSumData.create(false, AggregationTemporality.CUMULATIVE, g.map(toCounterDatum).asJava)
+
+  def convertCounter(counter: MetricSnapshot.Values[Long]): MetricData =
+    ImmutableMetricData.createLongSum(
+      resource,
+      instrumentationScopeInfo(counter),
+      counter.name,
+      counter.description,
+      toString(counter.settings.unit),
+      toCounterData(counter.instruments))
+
+}
 
 /**
  * Converts Kamon metrics to OpenTelemetry [[MetricData]]s
  */
 private[otel] object MetricsConverter {
-  def convert(resource: Resource, kamonVersion: String)(metrics: PeriodSnapshot): JCollection[MetricData] =
-    ???
+  def convert(resource: Resource, kamonVersion: String)(metrics: PeriodSnapshot): JCollection[MetricData] = {
+    val converter = new WithResourceMetricsConverter(resource, kamonVersion, metrics.from, metrics.to)
+    val gauges = metrics.gauges.map(converter.convertGauge)
+    val histograms = (metrics.histograms ++ metrics.timers ++ metrics.rangeSamplers).map(converter.convertHistogram)
+    val counters = metrics.counters.map(converter.convertCounter)
+
+    (gauges ++ histograms ++ counters).asJava
+  }
 }