Add other metric types and weight (part 2) (#1949)

* added crc32_utils.dart, taken from archive library
* added Gauge, Distribution and Set metrics
* added weight to Metrics and auto flush when weight is too much

* Add timing metric and beforeMetric callback (part 3) (#1954)
* added SentryOptions.beforeMetricCallback
* added beforeMetricCallback logic in metrics_aggregator.dart
* added timing metric api with span auto start
* timing api uses span duration as value for the emitted metric if possible

* Feat/metrics span summary p4 (#1958)
* added local_metrics_aggregator.dart to spans
* metrics_aggregator.dart now adds to current span's localMetricsAggregator
* added metric_summary.dart
* added metricSummary to spans and transaction JSONs

Author: stefanosiano

dart/lib/src/metrics/local_metrics_aggregator.dart

@@ -0,0 +1,37 @@
+import 'dart:core';
+import 'package:meta/meta.dart';
+import '../protocol/metric_summary.dart';
+import 'metric.dart';
+
+@internal
+class LocalMetricsAggregator {
+  // format: <export key, <metric key, gauge>>
+  final Map<String, Map<String, GaugeMetric>> _buckets = {};
+
+  void add(final Metric metric, final num value) {
+    final bucket =
+        _buckets.putIfAbsent(metric.getSpanAggregationKey(), () => {});
+
+    bucket.update(metric.getCompositeKey(), (m) => m..add(value),
+        ifAbsent: () => Metric.fromType(
+            type: MetricType.gauge,
+            key: metric.key,
+            value: value,
+            unit: metric.unit,
+            tags: metric.tags) as GaugeMetric);
+  }
+
+  Map<String, List<MetricSummary>> getSummaries() {
+    final Map<String, List<MetricSummary>> summaries = {};
+    for (final entry in _buckets.entries) {
+      final String exportKey = entry.key;
+
+      final metricSummaries = entry.value.values
+          .map((gauge) => MetricSummary.fromGauge(gauge))
+          .toList();
+
+      summaries[exportKey] = metricSummaries;
+    }
+    return summaries;
+  }
+}

dart/lib/src/metrics/metric.dart

@@ -1,3 +1,5 @@
+import 'dart:math';
+
 import 'package:meta/meta.dart';
 
 import '../../sentry.dart';
@@ -26,8 +28,31 @@ abstract class Metric {
     required this.tags,
   });
 
+  factory Metric.fromType({
+    required final MetricType type,
+    required final String key,
+    required final num value,
+    required final SentryMeasurementUnit unit,
+    required final Map<String, String> tags,
+  }) {
+    switch (type) {
+      case MetricType.counter:
+        return CounterMetric._(value: value, key: key, unit: unit, tags: tags);
+      case MetricType.gauge:
+        return GaugeMetric._(value: value, key: key, unit: unit, tags: tags);
+      case MetricType.set:
+        return SetMetric._(value: value, key: key, unit: unit, tags: tags);
+      case MetricType.distribution:
+        return DistributionMetric._(
+            value: value, key: key, unit: unit, tags: tags);
+    }
+  }
+
   /// Add a value to the metric.
-  add(double value);
+  add(num value);
+
+  /// Return the weight of the current metric.
+  int getWeight();
 
   /// Serialize the value into a list of Objects to be converted into a String.
   Iterable<Object> _serializeValue();
@@ -87,6 +112,10 @@ abstract class Metric {
     return ('${type.statsdType}_${key}_${unit.name}_$serializedTags');
   }
 
+  /// Return a key created by [key], [type] and [unit].
+  /// This key should be used to aggregate the metric locally in a span.
+  String getSpanAggregationKey() => '${type.statsdType}:$key@${unit.name}';
+
   /// Remove forbidden characters from the metric key and tag key.
   String _normalizeKey(String input) =>
       input.replaceAll(forbiddenKeyCharsRegex, '_');
@@ -100,31 +129,135 @@ abstract class Metric {
       input.replaceAll(forbiddenUnitCharsRegex, '_');
 }
 
-@internal
-
 /// Metric [MetricType.counter] that tracks a value that can only be incremented.
+@internal
 class CounterMetric extends Metric {
-  double value;
+  num value;
 
-  CounterMetric({
+  CounterMetric._({
     required this.value,
     required super.key,
     required super.unit,
     required super.tags,
   }) : super(type: MetricType.counter);
 
   @override
-  add(double value) => this.value += value;
+  add(num value) => this.value += value;
 
   @override
   Iterable<Object> _serializeValue() => [value];
+
+  @override
+  int getWeight() => 1;
 }
 
+/// Metric [MetricType.gauge] that tracks a value that can go up and down.
 @internal
+class GaugeMetric extends Metric {
+  num _last;
+  num _minimum;
+  num _maximum;
+  num _sum;
+  int _count;
+
+  GaugeMetric._({
+    required num value,
+    required super.key,
+    required super.unit,
+    required super.tags,
+  })  : _last = value,
+        _minimum = value,
+        _maximum = value,
+        _sum = value,
+        _count = 1,
+        super(type: MetricType.gauge);
+
+  @override
+  add(num value) {
+    _last = value;
+    _minimum = min(_minimum, value);
+    _maximum = max(_maximum, value);
+    _sum += value;
+    _count++;
+  }
+
+  @override
+  Iterable<Object> _serializeValue() =>
+      [_last, _minimum, _maximum, _sum, _count];
+
+  @override
+  int getWeight() => 5;
+
+  @visibleForTesting
+  num get last => _last;
+  num get minimum => _minimum;
+  num get maximum => _maximum;
+  num get sum => _sum;
+  int get count => _count;
+}
+
+/// Metric [MetricType.set] that tracks a set of values on which you can perform
+/// aggregations such as count_unique.
+@internal
+class SetMetric extends Metric {
+  final Set<int> _values = {};
+
+  SetMetric._(
+      {required num value,
+      required super.key,
+      required super.unit,
+      required super.tags})
+      : super(type: MetricType.set) {
+    add(value);
+  }
+
+  @override
+  add(num value) => _values.add(value.toInt());
+
+  @override
+  Iterable<Object> _serializeValue() => _values;
+
+  @override
+  int getWeight() => _values.length;
+
+  @visibleForTesting
+  Set<num> get values => _values;
+}
+
+/// Metric [MetricType.distribution] that tracks a list of values.
+@internal
+class DistributionMetric extends Metric {
+  final List<num> _values = [];
+
+  DistributionMetric._(
+      {required num value,
+      required super.key,
+      required super.unit,
+      required super.tags})
+      : super(type: MetricType.distribution) {
+    add(value);
+  }
+
+  @override
+  add(num value) => _values.add(value);
+
+  @override
+  Iterable<Object> _serializeValue() => _values;
+
+  @override
+  int getWeight() => _values.length;
+
+  @visibleForTesting
+  List<num> get values => _values;
+}
 
 /// The metric type and its associated statsd encoded value.
+@internal
 enum MetricType {
-  counter('c');
+  counter('c'),
+  gauge('g'),
+  distribution('d'),
+  set('s');
 
   final String statsdType;