From 3936b60eefe64b6664732fc7c1686bb0612c9edd Mon Sep 17 00:00:00 2001
From: Frank Imeson <frank.imeson@avidbots.com>
Date: Tue, 29 Sep 2020 10:20:54 -0400
Subject: [PATCH] CP-1935: Added some reset hooks for each metric type

---
 core/include/prometheus/counter.h     | 3 +++
 core/include/prometheus/gauge.h       | 3 +++
 core/include/prometheus/histogram.h   | 3 +++
 core/include/prometheus/metric_base.h | 2 +-
 core/src/counter.cc                   | 5 +++++
 core/src/gauge.cc                     | 6 ++++++
 core/src/histogram.cc                 | 9 +++++++++
 7 files changed, 30 insertions(+), 1 deletion(-)

diff --git a/core/include/prometheus/counter.h b/core/include/prometheus/counter.h
index 84ee8a4e..2e339658 100644
--- a/core/include/prometheus/counter.h
+++ b/core/include/prometheus/counter.h
@@ -34,6 +34,9 @@ class PROMETHEUS_CPP_CORE_EXPORT Counter: public MetricBase {
   /// \brief Create a counter that starts at 0.
   Counter(const bool alert_if_no_family = true);
 
+  /// \brief Resets the counter.
+  void Reset();
+
   /// \brief Increment the counter by a given amount.
   ///
   /// The counter will not change if the given amount is negative.
diff --git a/core/include/prometheus/gauge.h b/core/include/prometheus/gauge.h
index 0086f57a..f51c7af9 100644
--- a/core/include/prometheus/gauge.h
+++ b/core/include/prometheus/gauge.h
@@ -30,6 +30,9 @@ class PROMETHEUS_CPP_CORE_EXPORT Gauge: public MetricBase {
   /// \brief Create a gauge that starts at the given amount.
   Gauge(const double value = 0, const bool alert_if_no_family = true);
 
+  /// \brief Reset the gauge.
+  void Reset(const double value = 0);
+
   /// \brief Increment the gauge by the given amount.
   void Increment(const double value = 1);
 
diff --git a/core/include/prometheus/histogram.h b/core/include/prometheus/histogram.h
index 5fe1b68b..25c482bd 100644
--- a/core/include/prometheus/histogram.h
+++ b/core/include/prometheus/histogram.h
@@ -47,6 +47,9 @@ class PROMETHEUS_CPP_CORE_EXPORT Histogram: public MetricBase {
   /// The bucket boundaries cannot be changed once the histogram is created.
   Histogram(const BucketBoundaries& buckets, const bool alert_if_no_family = true);
 
+  /// \brief Reset the histogram.
+  void Reset();
+
   /// \brief Observe the given amount.
   ///
   /// The given amount selects the 'observed' bucket. The observed bucket is
diff --git a/core/include/prometheus/metric_base.h b/core/include/prometheus/metric_base.h
index 1846a741..09e58031 100644
--- a/core/include/prometheus/metric_base.h
+++ b/core/include/prometheus/metric_base.h
@@ -14,7 +14,7 @@ namespace prometheus {
 class PROMETHEUS_CPP_CORE_EXPORT MetricBase {
  public:
   MetricBase(const bool alert_if_no_family = true);
-  
+
   /// \brief    Prints a message to stderr if the metric doesn't have a family
   bool HasFamily();
 
diff --git a/core/src/counter.cc b/core/src/counter.cc
index 2b6397c2..7050f2e5 100644
--- a/core/src/counter.cc
+++ b/core/src/counter.cc
@@ -5,6 +5,11 @@ namespace prometheus {
 
 Counter::Counter(const bool alert_if_no_family) : MetricBase(alert_if_no_family) {};
 
+void Counter::Reset() {
+  value_ = 0;
+  last_update_ = std::time(nullptr);
+  AlertIfNoFamily();
+}
 
 void Counter::Increment(const double value) {
   if (value < 0.0) return;
diff --git a/core/src/gauge.cc b/core/src/gauge.cc
index e0d9b2c5..c4e612b2 100644
--- a/core/src/gauge.cc
+++ b/core/src/gauge.cc
@@ -7,6 +7,12 @@ namespace prometheus {
 
 Gauge::Gauge(const double value, const bool alert_if_no_family) : MetricBase(alert_if_no_family), value_(value) {}
 
+void Gauge::Reset(const double value) {
+  value_ = value;
+  last_update_ = std::time(nullptr);
+  AlertIfNoFamily();
+}
+
 void Gauge::Increment(const double value) {
   if (value < 0.0) return;
   value_ = value_ + value;
diff --git a/core/src/histogram.cc b/core/src/histogram.cc
index 7433a34f..22a5c213 100644
--- a/core/src/histogram.cc
+++ b/core/src/histogram.cc
@@ -13,6 +13,15 @@ Histogram::Histogram(const BucketBoundaries& buckets, const bool alert_if_no_fam
                         std::end(bucket_boundaries_)));
 }
 
+void Histogram::Reset() {
+  for (unsigned int bucket_index = 0; bucket_index < bucket_counts_.size(); ++bucket_index) {
+    bucket_counts_[bucket_index] = 0;
+  }  
+  sum_ = 0;
+  last_update_ = std::time(nullptr);
+  AlertIfNoFamily();
+}
+
 void Histogram::Observe(const double value) {
   // TODO: determine bucket list size at which binary search would be faster
   const auto bucket_index = static_cast<std::size_t>(std::distance(