module;

#include <boost/locale.hpp>
#include <unicode/localematcher.h>

export module routemon:locale;

import std;
import :util;

export namespace blocale = boost::locale;

export namespace routemon {

using lformat = blocale::format;
using blocale::gettext;
using blocale::translate;

} // namespace routemon

namespace routemon::locale {

export template <class T>
concept locale_input_range =
    std::ranges::input_range<T>
    && std::
        same_as<std::locale const&, std::ranges::range_const_reference_t<T>>;

// Helps select a locale based on the Accept-Language header in an
// HTTP request.
export class selector
{
  std::locale default_;
  icu::LocaleMatcher matcher_;
  std::shared_ptr<blocale::generator const> lgen_;

  auto make_matcher(
      locale_input_range auto supported_locales, std::locale default_locale)
  {
    auto builder = icu::LocaleMatcher::Builder{};
    for (auto const& supported_locale : supported_locales)
    {
      auto const& supported_locale_info =
          std::use_facet<blocale::info>(supported_locale);
      auto supported_icu_locale =
          icu::Locale{supported_locale_info.name().c_str()};
      if (supported_icu_locale.isBogus())
        throw std::runtime_error{
          "supported locale gives rise to bogus ICU locale"
        };
      builder.addSupportedLocale(supported_icu_locale);
    }
    auto const& default_locale_info =
        std::use_facet<blocale::info>(default_locale);
    auto default_icu_locale = icu::Locale{default_locale_info.name().c_str()};
    if (default_icu_locale.isBogus())
      throw std::runtime_error{"default locale gives rise to bogus ICU locale"};
    builder.setDefaultLocale(&default_icu_locale);
    auto ec = UErrorCode::U_ZERO_ERROR;
    auto matcher = builder.build(ec);
    if (U_FAILURE(ec))
      throw std::runtime_error{"failed to build icu::LocaleMatcher"};
    return matcher;
  }

  // Trimming optional whitespace as defined in RFC 9110, § 12.4.2.
  static auto ltrim_ows(std::string_view s) -> std::string_view;
  static auto rtrim_ows(std::string_view s) -> std::string_view;
  static auto trim_ows(std::string_view s) -> std::string_view;

  auto from_icu_locale(icu::Locale const& l) const -> std::locale;

public:
  // Note: lgen must live at least as long as the selector constructed here!
  // It is unfortunately not possible to copy/move a blocale::generator.
  explicit selector(
      locale_input_range auto locales, std::locale default_,
      std::shared_ptr<blocale::generator const> lgen)
    : default_{default_}, matcher_{make_matcher(locales, default_)}, lgen_{lgen}
  {
  }

  auto select(std::string_view accept_language) const -> std::locale;
};

auto to_bcp47_lang_tag(std::locale locale) -> std::optional<std::string>;

export auto make_generator() -> std::shared_ptr<blocale::generator const>;

} // namespace routemon::locale