validate.hpp

// Copyright (c) 2022, Tyler Weaver
//
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#pragma once
 
#include <fmt/format.h>
#include <fmt/ranges.h>
 
#include <cmath>
#include <limits>
#include <optional>
#include <range/v3/all.hpp>
 
#include "fp/result.hpp"
 
namespace fp {
 
template <typename T>
struct validate_range {
  T from = std::numeric_limits<T>::min();
  T to = std::numeric_limits<T>::max();
  std::optional<T> step = std::nullopt;
  double step_threshold = 1e-3;
 
  constexpr Result<T> operator()(T value, std::string const& name) const {
    if (value < from || value > to) {
      return tl::make_unexpected(OutOfRange(fmt::format(
          "{}: {} is outside of the range [{}, {}]", name, value, from, to)));
    }
 
    if (step) {
      double const step_value = static_cast<double>(step.value());
      double const ratio = static_cast<double>(value - from) / step_value;
      double const distance = fabs(ratio - round(ratio));
 
      if (distance > step_threshold) {
        return tl::make_unexpected(OutOfRange(
            fmt::format("{}: {} is {} away from the nearest valid step", name,
                        value, distance)));
      }
    }
 
    return value;
  }
};
 
template <typename Rng, typename T>
constexpr Result<T> validate_in(Rng const& valid_values, T const& value,
                                std::string const& name) {
  if (ranges::contains(valid_values, value)) {
    return value;
  }
  return tl::make_unexpected(
      OutOfRange(fmt::format("{} is not in {}", value, valid_values)));
  ;
}
 
}  // namespace fp