feat: add interface for metrics reporter (#7788)

The added interface specify how to report metrics to a metrics
framework. The implementations of this interface specify how to
report to a specific metrics framework (e.g. JMX or Confluent's
Telemetry pipeline)

ksqldb-engine/src/main/java/io/confluent/ksql/internal/MetricsReporter.java

@@ -0,0 +1,112 @@
+/*
+ * Copyright 2021 Confluent Inc.
+ *
+ * Licensed under the Confluent Community License (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.confluent.io/confluent-community-license
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+ * WARRANTIES OF ANY KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations under the License.
+ */
+
+package io.confluent.ksql.internal;
+
+import com.google.common.collect.ImmutableMap;
+import io.confluent.common.Configurable;
+
+import java.io.Closeable;
+import java.time.Instant;
+import java.util.Collections;
+import java.util.List;
+import java.util.Map;
+import java.util.Objects;
+import java.util.function.Supplier;
+
+/**
+ * This interface is used to report metrics as data points to a
+ * metrics framework.
+ * The implementations of this interface specify how to report to
+ * a specific metrics framework (e.g. JMX or Confluent's Telemetry
+ * pipeline)
+ */
+public interface MetricsReporter extends Closeable, Configurable {
+
+  /**
+   * A data point that should be reported.
+   */
+  class DataPoint {
+    private final String name;
+    private final Instant time;
+    private final Object value;
+    private final Map<String, String> tags;
+
+    public DataPoint(final Instant time, final String name, final Object value) {
+      this(time, name, value, Collections.emptyMap());
+    }
+
+    public DataPoint(
+        final Instant time,
+        final String name,
+        final Object value,
+        final Map<String, String> tags
+    ) {
+      this.name = Objects.requireNonNull(name, "name");
+      this.time = Objects.requireNonNull(time, "time");
+      this.value = Objects.requireNonNull(value, "value");
+      this.tags = ImmutableMap.copyOf(Objects.requireNonNull(tags, "tags"));
+    }
+
+    public String getName() {
+      return name;
+    }
+
+    public Instant getTime() {
+      return time;
+    }
+
+    public Object getValue() {
+      return value;
+    }
+
+    public Map<String, String> getTags() {
+      return tags;
+    }
+
+    @Override
+    public boolean equals(final Object o) {
+      if (this == o) {
+        return true;
+      }
+      if (o == null || getClass() != o.getClass()) {
+        return false;
+      }
+      final DataPoint dataPoint = (DataPoint) o;
+      return time == dataPoint.time
+          && value == dataPoint.value
+          && Objects.equals(name, dataPoint.name)
+          && Objects.equals(tags, dataPoint.tags);
+    }
+
+    @Override
+    public String toString() {
+      return "DataPoint{" + "name='" + name + '\''
+          + ", time=" + time + ", value=" + value + ", tags=" + tags + '}';
+    }
+
+    @Override
+    public int hashCode() {
+      return Objects.hash(name, time, value, tags);
+    }
+  }
+
+  /**
+   * Reports a list of data points.
+   *
+   * @param dataPointSupplier supplier of the list of data points
+   */
+  void report(Supplier<List<DataPoint>> dataPointSupplier);
+}