key_value_iterable_view.h

// Copyright The OpenTelemetry Authors
// SPDX-License-Identifier: Apache-2.0

#pragma once

#include <stddef.h>
#include <initializer_list>
#include <iterator>
#include <type_traits>
#include <utility>
#include <vector>

#include "opentelemetry/common/attribute_value.h"
#include "opentelemetry/common/key_value_iterable.h"
#include "opentelemetry/nostd/function_ref.h"
#include "opentelemetry/nostd/span.h"
#include "opentelemetry/nostd/string_view.h"
#include "opentelemetry/nostd/type_traits.h"
#include "opentelemetry/nostd/utility.h"
#include "opentelemetry/version.h"

OPENTELEMETRY_BEGIN_NAMESPACE
namespace common
{
// NOTE - code within `detail` namespace implements internal details, and not part
// of the public interface.
namespace detail
{
inline void take_key_value(nostd::string_view, common::AttributeValue) {}

template <class T>
auto is_key_value_iterable_impl(T iterable)
    -> decltype(take_key_value(std::begin(iterable)->first, std::begin(iterable)->second),
                nostd::size(iterable),
                std::true_type{});

std::false_type is_key_value_iterable_impl(...);

template <class T>
struct is_key_value_iterable
{
  static const bool value = decltype(detail::is_key_value_iterable_impl(std::declval<T>()))::value;
};
}  // namespace detail

/**
 * @brief Container for key-value pairs that can transform every value in it to one of types
 * listed in common::AttributeValue. It may contain value types that are not directly map'able
 * to primitive value types. In that case the `ForEachKeyValue` method acts as a transform to
 * convert the value type to one listed under AtributeValue (bool, int32_t, int64_t, uint32_t,
 * uint64_t, double, nostd::string_view, or arrays of primite types). For example, if UUID,
 * GUID, or UTF-16 string type is passed as one of values stored inside this container, the
 * container itself may provide a custom implementation of `ForEachKeyValue` to transform the
 * 'non-standard' type to one of the standard types.
 */
template <class T>
class KeyValueIterableView final : public KeyValueIterable
{

public:
  explicit KeyValueIterableView(const T &container) noexcept : container_{&container} {}

  // KeyValueIterable
  bool ForEachKeyValue(nostd::function_ref<bool(nostd::string_view, common::AttributeValue)>
                           callback) const noexcept override
  {
    auto iter = std::begin(*container_);
    auto last = std::end(*container_);
    for (; iter != last; ++iter)
    {
      if (!callback(iter->first, iter->second))
      {
        return false;
      }
    }
    return true;
  }

  size_t size() const noexcept override { return nostd::size(*container_); }

private:
  const T *container_;
};

template <class T, nostd::enable_if_t<detail::is_key_value_iterable<T>::value> * = nullptr>
KeyValueIterableView<T> MakeKeyValueIterableView(const T &container) noexcept
{
  return KeyValueIterableView<T>(container);
}

/**
 * Utility function to help to make a attribute view from initializer_list
 *
 * @param attributes The initializer_list of key-value pairs
 * @return nostd::span<const std::pair<nostd::string_view, common::AttributeValue>>
 */
inline static nostd::span<const std::pair<nostd::string_view, common::AttributeValue>>
MakeAttributes(std::initializer_list<std::pair<nostd::string_view, common::AttributeValue>>
                   attributes) noexcept
{
  return nostd::span<const std::pair<nostd::string_view, common::AttributeValue>>{
      attributes.begin(), attributes.end()};
}

/**
 * Utility function to help to make a attribute view from a span
 *
 * @param attributes The span of key-value pairs
 * @return nostd::span<const std::pair<nostd::string_view, common::AttributeValue>>
 */
inline static nostd::span<const std::pair<nostd::string_view, common::AttributeValue>>
MakeAttributes(
    nostd::span<const std::pair<nostd::string_view, common::AttributeValue>> attributes) noexcept
{
  return attributes;
}

/**
 * Utility function to help to make a attribute view from a KeyValueIterable
 *
 * @param attributes The KeyValueIterable of key-value pairs
 * @return common::KeyValueIterable
 */
inline static const common::KeyValueIterable &MakeAttributes(
    const common::KeyValueIterable &attributes OPENTELEMETRY_ATTRIBUTE_LIFETIME_BOUND) noexcept
{
  return attributes;
}

/**
 * Utility function to help to make a attribute view from a key-value iterable object
 *
 * @tparam ArgumentType  Expected to be ArgumentType
 * @param attributes     The key-value iterable object
 * @return nostd::span<const std::pair<nostd::string_view, common::AttributeValue>>
 */
template <
    class ArgumentType,
    nostd::enable_if_t<common::detail::is_key_value_iterable<ArgumentType>::value> * = nullptr>
inline static common::KeyValueIterableView<ArgumentType> MakeAttributes(
    const ArgumentType &attributes) noexcept
{
  return common::KeyValueIterableView<ArgumentType>(attributes);
}

}  // namespace common
OPENTELEMETRY_END_NAMESPACE