Transform strings into a canonical representation

make_canonical.hpp

/// @file make_canonical.hpp
/// @brief Transform strings into a canonical representation.
/// @author J. Arrieta <Juan.Arrieta@nablazerolabs.com>
/// @copyright (C) 2019 Nabla Zero Labs
/// @license MIT

#pragma once

#include <algorithm>
#include <cctype>
#include <cwctype>
#include <string>

namespace {

template <typename T>
inline bool is_not_space(T c);

template <typename T>
inline T downcase(T c);

template <>
inline bool is_not_space(char c) {
  return !std::isspace(c);
}

template <>
inline bool is_not_space(wchar_t c) {
  return !std::iswspace(c);
}

template <>
inline char downcase(char c) {
  return std::tolower(c);
}

template <>
inline wchar_t downcase(wchar_t c) {
  return std::towlower(c);
}

}  // anonymous namespace

namespace nzl {

/// @brief Return a canonical string representation.
/// @param value String to canonicalize.
/// @return A canonical representation of @p value.
/// @note The canonical representation of a string is obtained when all leading
/// and trailing whitespace is removed and all characters are downcased.
/// @note This implementation only supports ASCII encoding.
template <typename CharT, typename Traits = std::char_traits<CharT>,
          typename Allocator = std::allocator<CharT> >
inline auto make_canonical(std::basic_string_view<CharT, Traits> value) {
  std::basic_string<CharT, Traits, Allocator> s(value);

  // remove leading whitespace
  s.erase(s.begin(), std::find_if(s.begin(), s.end(), is_not_space<CharT>));

  // remove trailing whitespace
  s.erase(std::find_if(s.rbegin(), s.rend(), is_not_space<CharT>).base(),
          s.end());

  // downcase all chars
  std::transform(s.begin(), s.end(), s.begin(), downcase<CharT>);

  return s;
}

inline auto make_canonical(const char* c) {
  return make_canonical(std::basic_string_view<char>(c));
}

inline auto make_canonical(const wchar_t* c) {
  return make_canonical(std::basic_string_view<wchar_t>(c));
}

inline auto make_canonical(const std::string& c) {
  return make_canonical(std::basic_string_view<char>(c));
}

inline auto make_canonical(const std::wstring& c) {
  return make_canonical(std::basic_string_view<wchar_t>(c));
}

}  // namespace nzl