Improve Summarizer ergonomics

Author: cwaldren-ld

libs/common/include/events/detail/summarizer.hpp

@@ -30,13 +30,19 @@ class Summarizer {
      * Construct a Summarizer at time zero.
      */
     Summarizer() = default;
-    
+
     /**
      * Updates the summary with a feature event.
      * @param event Feature event.
      */
     void Update(client::FeatureEventParams const& event);
 
+    /**
+     * Marks the summary as finished at a given timestamp.
+     * @param end_time End time of the summary.
+     */
+    Summarizer& Finish(Time end_time);
+
     /**
      * Returns true if the summary is empty.
      */
@@ -47,6 +53,11 @@ class Summarizer {
      */
     [[nodiscard]] Time start_time() const;
 
+    /**
+     * Returns the summary's end time as specified using Finish.
+     */
+    [[nodiscard]] Time end_time() const;
+
     struct VariationSummary {
        public:
         explicit VariationSummary(Value value);
@@ -95,12 +106,8 @@ class Summarizer {
 
    private:
     Time start_time_;
+    Summarizer::Time end_time_;
     std::unordered_map<FlagKey, State> features_;
 };
 
-struct Summary {
-    Summarizer const& summarizer;
-    Summarizer::Time end_time;
-};
-
 }  // namespace launchdarkly::events::detail

libs/common/include/serialization/events/json_events.hpp

@@ -46,5 +46,5 @@ void tag_invoke(boost::json::value_from_tag const&,
                 Summarizer::State const& state);
 void tag_invoke(boost::json::value_from_tag const&,
                 boost::json::value& json_value,
-                Summary const& summary);
+                Summarizer const& summary);
 }  // namespace launchdarkly::events::detail

libs/common/src/events/asio_event_processor.cpp

@@ -132,9 +132,8 @@ AsioEventProcessor::MakeRequest() {
 
     auto events = boost::json::value_from(outbox_.Consume());
 
-    if (!summarizer_.Empty()) {
-        events.as_array().push_back(boost::json::value_from(
-            Summary{summarizer_, std::chrono::system_clock::now()}));
+    if (!summarizer_.Finish(std::chrono::system_clock::now()).Empty()) {
+        events.as_array().push_back(boost::json::value_from(summarizer_));
     }
 
     LD_LOG(logger_, LogLevel::kDebug)

libs/common/src/events/summarizer.cpp

@@ -53,10 +53,19 @@ void Summarizer::Update(client::FeatureEventParams const& event) {
     summary_counter->second.Increment();
 }
 
+Summarizer& Summarizer::Finish(Time end_time) {
+    end_time_ = end_time;
+    return *this;
+}
+
 Summarizer::Time Summarizer::start_time() const {
     return start_time_;
 }
 
+Summarizer::Time Summarizer::end_time() const {
+    return end_time_;
+}
+
 Summarizer::VariationKey::VariationKey(Version version,
                                        std::optional<VariationIndex> variation)
     : version(version), variation(variation) {}

libs/common/src/serialization/events/json_events.cpp

@@ -113,13 +113,12 @@ void tag_invoke(boost::json::value_from_tag const& tag,
 }
 void tag_invoke(boost::json::value_from_tag const& tag,
                 boost::json::value& json_value,
-                Summary const& summary) {
+                Summarizer const& summary) {
     auto& obj = json_value.emplace_object();
     obj.emplace("kind", "summary");
     obj.emplace("startDate",
-                boost::json::value_from(Date{summary.summarizer.start_time()}));
-    obj.emplace("endDate", boost::json::value_from(Date{summary.end_time}));
-    obj.emplace("features",
-                boost::json::value_from(summary.summarizer.features()));
+                boost::json::value_from(Date{summary.start_time()}));
+    obj.emplace("endDate", boost::json::value_from(Date{summary.end_time()}));
+    obj.emplace("features", boost::json::value_from(summary.features()));
 }
 }  // namespace launchdarkly::events::detail

libs/common/tests/event_processor_test.cpp

@@ -12,18 +12,22 @@
 
 using namespace launchdarkly::events::detail;
 
-static std::chrono::system_clock::time_point ZeroTime() {
+static std::chrono::system_clock::time_point TimeZero() {
     return std::chrono::system_clock::time_point{};
 }
 
+static std::chrono::system_clock::time_point Time1000() {
+    return std::chrono::system_clock::from_time_t(1);
+}
+
 TEST(SummarizerTests, IsEmptyOnConstruction) {
     Summarizer summarizer;
     ASSERT_TRUE(summarizer.Empty());
 }
 
 TEST(SummarizerTests, DefaultConstructionUsesZeroStartTime) {
     Summarizer summarizer;
-    ASSERT_EQ(summarizer.start_time(), ZeroTime());
+    ASSERT_EQ(summarizer.start_time(), TimeZero());
 }
 
 TEST(SummarizerTests, ExplicitStartTimeIsCorrect) {
@@ -45,7 +49,7 @@ TEST(SummarizerTests, SummaryCounterUpdates) {
     auto const feature_variation = 0;
 
     auto const event = FeatureEventParams{
-        ZeroTime(),
+        TimeZero(),
         feature_key,
         context,
         EvaluationResult(
@@ -88,7 +92,7 @@ TEST(SummarizerTests, JsonSerialization) {
     auto const feature_variation = 0;
 
     auto const event = FeatureEventParams{
-        ZeroTime(),
+        TimeZero(),
         feature_key,
         context,
         EvaluationResult(
@@ -105,10 +109,9 @@ TEST(SummarizerTests, JsonSerialization) {
     for (size_t i = 0; i < num_events; i++) {
         summarizer.Update(event);
     }
-
-    auto json = boost::json::value_from(Summary{summarizer, ZeroTime()});
+    auto json = boost::json::value_from(summarizer.Finish(Time1000()));
     auto expected = boost::json::parse(
-        R"({"kind":"summary","startDate":0,"endDate":0,"features":{"cat-food-amount":{"default":1E0,"contextKinds":["cat"],"counters":[{"version":1,"variation":0,"value":3E0,"count":10}]}}})");
+        R"({"kind":"summary","startDate":0,"endDate":1000,"features":{"cat-food-amount":{"default":1E0,"contextKinds":["cat"],"counters":[{"version":1,"variation":0,"value":3E0,"count":10}]}}})");
     ASSERT_EQ(json, expected);
 }