text: // Copyright The OpenTelemetry Authors
  // SPDX-License-Identifier: Apache-2.0
  
  #pragma once
  #ifndef ENABLE_METRICS_PREVIEW
  
  #  include "opentelemetry/common/attribute_value.h"
  #  include "opentelemetry/common/key_value_iterable_view.h"
  #  include "opentelemetry/nostd/span.h"
  #  include "opentelemetry/nostd/string_view.h"
  #  include "opentelemetry/nostd/type_traits.h"
  
  OPENTELEMETRY_BEGIN_NAMESPACE
  namespace metrics
  {
  
  class SynchronousInstrument
  {};
  
  template <class T>
  class Counter : public SynchronousInstrument
  {
  
  public:
    /**
     * Add adds the value to the counter's sum
     *
     * @param value The increment amount. MUST be non-negative.
     */
    virtual void Add(T value) noexcept = 0;
  
    /**
     * Add adds the value to the counter's sum. The attributes should contain
     * the keys and values to be associated with this value.  Counters only
     * accept positive valued updates.
     *
     * @param value The increment amount. MUST be non-negative.
     * @param attributes the set of attributes, as key-value pairs
     */
  
    virtual void Add(T value, const common::KeyValueIterable &attributes) noexcept = 0;
  
    template <class U,
              nostd::enable_if_t<common::detail::is_key_value_iterable<U>::value> * = nullptr>
    void Add(T value, const U &attributes) noexcept
    {
      this->Add(value, common::KeyValueIterableView<U>{attributes});
    }
  
    void Add(T value,
             std::initializer_list<std::pair<nostd::string_view, common::AttributeValue>>
                 attributes) noexcept
    {
      this->Add(value, nostd::span<const std::pair<nostd::string_view, common::AttributeValue>>{
                           attributes.begin(), attributes.end()});
    }
  };
  
  /** A histogram instrument that records values. */
  
  template <class T>
  class Histogram : public SynchronousInstrument
  {
  public:
    /**
     * Records a value.
     *
     * @param value The increment amount. May be positive, negative or zero.
     */
    virtual void Record(T value) noexcept = 0;
  
    /**
     * Records a value with a set of attributes.
     *
     * @param value The increment amount. May be positive, negative or zero.
     * @param attributes A set of attributes to associate with the count.
     */
    virtual void Record(T value, const common::KeyValueIterable &attributes) noexcept = 0;
  
    template <class U,
              nostd::enable_if_t<common::detail::is_key_value_iterable<U>::value> * = nullptr>
    void Record(T value, const U &attributes) noexcept
    {
      this->Record(value, common::KeyValueIterableView<U>{attributes});
    }
  
    void Record(T value,
                std::initializer_list<std::pair<nostd::string_view, common::AttributeValue>>
                    attributes) noexcept
    {
      this->Record(value, nostd::span<const std::pair<nostd::string_view, common::AttributeValue>>{
                              attributes.begin(), attributes.end()});
    }
  };
  
  /** An up-down-counter instrument that adds or reduce values. */
  
  template <class T>
  class UpDownCounter : public SynchronousInstrument
  {
  public:
    /**
     * Adds a value.
     *
     * @param value The amount of the measurement.
     */
    virtual void Add(T value) noexcept = 0;
  
    /**
     * Add a value with a set of attributes.
     *
     * @param value The increment amount. May be positive, negative or zero.
     * @param attributes A set of attributes to associate with the count.
     */
    virtual void Add(T value, const common::KeyValueIterable &attributes) noexcept = 0;
  
    template <class U,
              nostd::enable_if_t<common::detail::is_key_value_iterable<U>::value> * = nullptr>
    void Add(T value, const U &attributes) noexcept
    {
      this->Add(value, common::KeyValueIterableView<U>{attributes});
    }
  
    void Add(T value,
             std::initializer_list<std::pair<nostd::string_view, common::AttributeValue>>
                 attributes) noexcept
    {
      this->Add(value, nostd::span<const std::pair<nostd::string_view, common::AttributeValue>>{
                           attributes.begin(), attributes.end()});
    }
  };
  
  }  // namespace metrics
  OPENTELEMETRY_END_NAMESPACE
  #endif
  