ENG-44604: Add metrics to count no. of API entities per category per tenant (#285)

* add metric

* minor refactor

* corrected attribute paths

Author: aditya-choubey2512

entity-service-impl/src/main/java/org/hypertrace/entity/metric/EntityMetricsReporter.java

@@ -10,6 +10,7 @@
 import org.hypertrace.core.documentstore.expression.impl.ConstantExpression;
 import org.hypertrace.core.documentstore.expression.impl.IdentifierExpression;
 import org.hypertrace.core.documentstore.expression.impl.RelationalExpression;
+import org.hypertrace.core.documentstore.expression.impl.UnnestExpression;
 import org.hypertrace.core.documentstore.expression.operators.RelationalOperator;
 import org.hypertrace.core.documentstore.model.config.CustomMetricConfig;
 import org.hypertrace.core.documentstore.query.Filter;
@@ -22,10 +23,15 @@
 public class EntityMetricsReporter {
 
   private static final String API_COUNT_METRIC_NAME = "api.entities.count";
+  private static final String API_CATEGORY_METRIC_NAME = "api.categories.count";
   private static final String RAW_ENTITIES_COLLECTION = "raw_entities";
   private static final String API_DISCOVERY_STATE_ENTITY_PATH =
       "attributes.api_discovery_state.value.string";
+  private static final String API_CATEGORIES_ENTITY_PATH = "attributes.categories.valueList.values";
+  private static final String API_CATEGORY_ENTITY_PATH =
+      "attributes.categories.valueList.values.value.string";
   private static final String API_DISCOVERY_STATE = "apiDiscoveryState";
+  private static final String API_CATEGORY = "category";
   private static final String TENANT_ID_ENTITY_PATH = "tenantId";
   private static final String ENTITY_TYPE_ENTITY_PATH = "entityType";
   private final DocStoreMetricsRegistry metricsRegistry;
@@ -66,6 +72,31 @@ public void monitor() {
                                   IdentifierExpression.of(API_DISCOVERY_STATE_ENTITY_PATH))
                               .build())
                       .build())
+              .build(),
+          DocStoreCustomMetricReportingConfig.builder()
+              .reportingInterval(Duration.ofHours(6))
+              .config(
+                  CustomMetricConfig.builder()
+                      .metricName(API_CATEGORY_METRIC_NAME)
+                      .collectionName(RAW_ENTITIES_COLLECTION)
+                      .query(
+                          Query.builder()
+                              .setFilter(getFilter())
+                              .addFromClause(
+                                  UnnestExpression.builder()
+                                      .identifierExpression(
+                                          IdentifierExpression.of(API_CATEGORIES_ENTITY_PATH))
+                                      .build())
+                              .addSelection(IdentifierExpression.of(TENANT_ID_ENTITY_PATH))
+                              .addSelection(
+                                  IdentifierExpression.of(API_CATEGORY_ENTITY_PATH), API_CATEGORY)
+                              .addSelection(
+                                  AggregateExpression.of(COUNT, ConstantExpression.of(1)),
+                                  VALUE_KEY)
+                              .addAggregation(IdentifierExpression.of(TENANT_ID_ENTITY_PATH))
+                              .addAggregation(IdentifierExpression.of(API_CATEGORY_ENTITY_PATH))
+                              .build())
+                      .build())
               .build());
 
   private Filter getFilter() {