1 files changed, 153 insertions, 0 deletions
diff --git a/kamon-core/src/main/scala/kamon/metric/MetricKey.scala b/kamon-core/src/main/scala/kamon/metric/MetricKey.scala
new file mode 100644
index 00000000..a17972df
--- /dev/null
+++ b/kamon-core/src/main/scala/kamon/metric/MetricKey.scala
@@ -0,0 +1,153 @@
+package kamon.metric
+
+import kamon.metric.instrument.{ InstrumentTypes, InstrumentType, UnitOfMeasurement }
+
+/**
+ *  MetricKeys are used to identify a given metric in entity recorders and snapshots. MetricKeys can be used to encode
+ *  additional metadata for a metric being recorded, as well as the unit of measurement of the data being recorder.
+ */
+sealed trait MetricKey {
+  def name: String
+  def unitOfMeasurement: UnitOfMeasurement
+  def instrumentType: InstrumentType
+  def metadata: Map[String, String]
+}
+
+// Wish that there was a shorter way to describe the operations bellow, but apparently there is no way to generalize all
+// the apply/create versions that would produce the desired return types when used from Java.
+
+/**
+ *  MetricKey for all Histogram-based metrics.
+ */
+case class HistogramKey(name: String, unitOfMeasurement: UnitOfMeasurement, metadata: Map[String, String]) extends MetricKey {
+  val instrumentType = InstrumentTypes.Histogram
+}
+
+object HistogramKey {
+  def apply(name: String): HistogramKey =
+    apply(name, UnitOfMeasurement.Unknown)
+
+  def apply(name: String, unitOfMeasurement: UnitOfMeasurement): HistogramKey =
+    apply(name, unitOfMeasurement, Map.empty)
+
+  def apply(name: String, metadata: Map[String, String]): HistogramKey =
+    apply(name, UnitOfMeasurement.Unknown, Map.empty)
+
+  /**
+   *  Java friendly versions:
+   */
+
+  def create(name: String): HistogramKey =
+    apply(name, UnitOfMeasurement.Unknown)
+
+  def create(name: String, unitOfMeasurement: UnitOfMeasurement): HistogramKey =
+    apply(name, unitOfMeasurement)
+
+  def create(name: String, metadata: Map[String, String]): HistogramKey =
+    apply(name, metadata)
+
+  def create(name: String, unitOfMeasurement: UnitOfMeasurement, metadata: Map[String, String]): HistogramKey =
+    apply(name, unitOfMeasurement, metadata)
+}
+
+/**
+ *  MetricKey for all MinMaxCounter-based metrics.
+ */
+case class MinMaxCounterKey(name: String, unitOfMeasurement: UnitOfMeasurement, metadata: Map[String, String]) extends MetricKey {
+  val instrumentType = InstrumentTypes.MinMaxCounter
+}
+
+object MinMaxCounterKey {
+  def apply(name: String): MinMaxCounterKey =
+    apply(name, UnitOfMeasurement.Unknown)
+
+  def apply(name: String, unitOfMeasurement: UnitOfMeasurement): MinMaxCounterKey =
+    apply(name, unitOfMeasurement, Map.empty)
+
+  def apply(name: String, metadata: Map[String, String]): MinMaxCounterKey =
+    apply(name, UnitOfMeasurement.Unknown, Map.empty)
+
+  /**
+   *  Java friendly versions:
+   */
+
+  def create(name: String): MinMaxCounterKey =
+    apply(name, UnitOfMeasurement.Unknown)
+
+  def create(name: String, unitOfMeasurement: UnitOfMeasurement): MinMaxCounterKey =
+    apply(name, unitOfMeasurement)
+
+  def create(name: String, metadata: Map[String, String]): MinMaxCounterKey =
+    apply(name, metadata)
+
+  def create(name: String, unitOfMeasurement: UnitOfMeasurement, metadata: Map[String, String]): MinMaxCounterKey =
+    apply(name, unitOfMeasurement, metadata)
+}
+
+/**
+ *  MetricKey for all Gauge-based metrics.
+ */
+case class GaugeKey(name: String, unitOfMeasurement: UnitOfMeasurement, metadata: Map[String, String]) extends MetricKey {
+  val instrumentType = InstrumentTypes.Gauge
+}
+
+object GaugeKey {
+  def apply(name: String): GaugeKey =
+    apply(name, UnitOfMeasurement.Unknown)
+
+  def apply(name: String, unitOfMeasurement: UnitOfMeasurement): GaugeKey =
+    apply(name, unitOfMeasurement, Map.empty)
+
+  def apply(name: String, metadata: Map[String, String]): GaugeKey =
+    apply(name, UnitOfMeasurement.Unknown, Map.empty)
+
+  /**
+   *  Java friendly versions:
+   */
+
+  def create(name: String): GaugeKey =
+    apply(name, UnitOfMeasurement.Unknown)
+
+  def create(name: String, unitOfMeasurement: UnitOfMeasurement): GaugeKey =
+    apply(name, unitOfMeasurement)
+
+  def create(name: String, metadata: Map[String, String]): GaugeKey =
+    apply(name, metadata)
+
+  def create(name: String, unitOfMeasurement: UnitOfMeasurement, metadata: Map[String, String]): GaugeKey =
+    apply(name, unitOfMeasurement, metadata)
+}
+
+/**
+ *  MetricKey for all Counter-based metrics.
+ */
+case class CounterKey(name: String, unitOfMeasurement: UnitOfMeasurement, metadata: Map[String, String]) extends MetricKey {
+  val instrumentType = InstrumentTypes.Counter
+}
+
+object CounterKey {
+  def apply(name: String): CounterKey =
+    apply(name, UnitOfMeasurement.Unknown)
+
+  def apply(name: String, unitOfMeasurement: UnitOfMeasurement): CounterKey =
+    apply(name, unitOfMeasurement, Map.empty)
+
+  def apply(name: String, metadata: Map[String, String]): CounterKey =
+    apply(name, UnitOfMeasurement.Unknown, Map.empty)
+
+  /**
+   *  Java friendly versions:
+   */
+
+  def create(name: String): CounterKey =
+    apply(name, UnitOfMeasurement.Unknown)
+
+  def create(name: String, unitOfMeasurement: UnitOfMeasurement): CounterKey =
+    apply(name, unitOfMeasurement)
+
+  def create(name: String, metadata: Map[String, String]): CounterKey =
+    apply(name, metadata)
+
+  def create(name: String, unitOfMeasurement: UnitOfMeasurement, metadata: Map[String, String]): CounterKey =
+    apply(name, unitOfMeasurement, metadata)
+}
+\ No newline at end of file