add minimalist exporter for Prometheus

Author: fupelaqu

core/src/main/scala/app/softnetwork/elastic/client/monitoring/PrometheusExporter.scala

@@ -0,0 +1,33 @@
+package app.softnetwork.elastic.client.monitoring
+
+import app.softnetwork.elastic.client.metrics.MetricsElasticClient
+
+trait PrometheusExporter { self: MetricsElasticClient =>
+
+  def exportPrometheusMetrics: String = {
+    val aggregated = getAggregatedMetrics
+    val sb = new StringBuilder()
+
+    // Global metrics
+    sb.append(s"elasticsearch_operations_total ${aggregated.totalOperations}\n")
+    sb.append(s"elasticsearch_operations_success ${aggregated.successCount}\n")
+    sb.append(s"elasticsearch_operations_failure ${aggregated.failureCount}\n")
+    sb.append(s"elasticsearch_operations_duration_ms ${aggregated.totalDuration}\n")
+
+    // Per-operation metrics
+    aggregated.operationMetrics.foreach { case (op, m) =>
+      sb.append(s"""elasticsearch_operation_total{operation="$op"} ${m.totalOperations}""" + "\n")
+      sb.append(s"""elasticsearch_operation_duration_ms{operation="$op"} ${m.totalDuration}""" + "\n")
+      sb.append(s"""elasticsearch_operation_success_rate{operation="$op"} ${m.successRate}""" + "\n")
+    }
+
+    // Per-index metrics
+    aggregated.indexMetrics.foreach { case (idx, m) =>
+      sb.append(s"""elasticsearch_index_operations{index="$idx"} ${m.totalOperations}""" + "\n")
+      sb.append(s"""elasticsearch_index_duration_ms{index="$idx"} ${m.totalDuration}""" + "\n")
+    }
+
+    sb.toString()
+  }
+}
+