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#pragma once
#include <mutex>
#include <vector>
#include "prometheus/client_metric.h"
#include "prometheus/counter.h"
#include "prometheus/detail/builder.h" // IWYU pragma: export
#include "prometheus/detail/core_export.h"
#include "prometheus/gauge.h"
#include "prometheus/metric_type.h"
namespace prometheus {
/// \brief A histogram metric to represent aggregatable distributions of events.
///
/// This class represents the metric type histogram:
/// https://prometheus.io/docs/concepts/metric_types/#histogram
///
/// A histogram tracks the number of observations and the sum of the observed
/// values, allowing to calculate the average of the observed values.
///
/// At its core a histogram has a counter per bucket. The sum of observations
/// also behaves like a counter as long as there are no negative observations.
///
/// See https://prometheus.io/docs/practices/histograms/ for detailed
/// explanations of histogram usage and differences to summaries.
///
/// The class is thread-safe. No concurrent call to any API of this type causes
/// a data race.
class PROMETHEUS_CPP_CORE_EXPORT Histogram {
public:
using BucketBoundaries = std::vector<double>;
static const MetricType metric_type{MetricType::Histogram};
/// \brief Create a histogram with manually chosen buckets.
///
/// The BucketBoundaries are a list of monotonically increasing values
/// representing the bucket boundaries. Each consecutive pair of values is
/// interpreted as a half-open interval [b_n, b_n+1) which defines one bucket.
///
/// There is no limitation on how the buckets are divided, i.e, equal size,
/// exponential etc..
///
/// The bucket boundaries cannot be changed once the histogram is created.
Histogram(const BucketBoundaries& buckets);
/// \brief Observe the given amount.
///
/// The given amount selects the 'observed' bucket. The observed bucket is
/// chosen for which the given amount falls into the half-open interval [b_n,
/// b_n+1). The counter of the observed bucket is incremented. Also the total
/// sum of all observations is incremented.
void Observe(double value);
/// \brief Observe multiple data points.
///
/// Increments counters given a count for each bucket. (i.e. the caller of
/// this function must have already sorted the values into buckets).
/// Also increments the total sum of all observations by the given value.
void ObserveMultiple(const std::vector<double>& bucket_increments,
const double sum_of_values);
/// \brief Get the current value of the counter.
///
/// Collect is called by the Registry when collecting metrics.
ClientMetric Collect() const;
private:
const BucketBoundaries bucket_boundaries_;
mutable std::mutex mutex_;
std::vector<Counter> bucket_counts_;
Gauge sum_;
};
/// \brief Return a builder to configure and register a Histogram metric.
///
/// @copydetails Family<>::Family()
///
/// Example usage:
///
/// \code
/// auto registry = std::make_shared<Registry>();
/// auto& histogram_family = prometheus::BuildHistogram()
/// .Name("some_name")
/// .Help("Additional description.")
/// .Labels({{"key", "value"}})
/// .Register(*registry);
///
/// ...
/// \endcode
///
/// \return An object of unspecified type T, i.e., an implementation detail
/// except that it has the following members:
///
/// - Name(const std::string&) to set the metric name,
/// - Help(const std::string&) to set an additional description.
/// - Labels(const Labels&) to assign a set of
/// key-value pairs (= labels) to the metric.
///
/// To finish the configuration of the Histogram metric register it with
/// Register(Registry&).
PROMETHEUS_CPP_CORE_EXPORT detail::Builder<Histogram> BuildHistogram();
} // namespace prometheus
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