cpp/src/language.cc

// Copyright (C) 2014 Google Inc.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

#include "language.h"

#include <algorithm>
#include <cctype>
#include <string>
#include <vector>

#include "rule.h"
#include "util/string_split.h"

namespace i18n {
namespace addressinput {

Language::Language(const std::string& language_tag) : tag(language_tag),
                                                      base(),
                                                      has_latin_script(false) {
  // Character '-' is the separator for subtags in the BCP 47. However, some
  // legacy code generates tags with '_' instead of '-'.
  static const char kSubtagsSeparator = '-';
  static const char kAlternativeSubtagsSeparator = '_';
  std::replace(
      tag.begin(), tag.end(), kAlternativeSubtagsSeparator, kSubtagsSeparator);

  // OK to use 'tolower' because BCP 47 tags are always in ASCII.
  std::string lowercase = tag;
  std::transform(
      lowercase.begin(), lowercase.end(), lowercase.begin(), tolower);

  base = lowercase.substr(0, lowercase.find(kSubtagsSeparator));

  // The lowercase BCP 47 subtag for Latin script.
  static const char kLowercaseLatinScript[] = "latn";
  std::vector<std::string> subtags;
  SplitString(lowercase, kSubtagsSeparator, &subtags);

  // Support only the second and third position for the script.
  has_latin_script =
      (subtags.size() > 1 && subtags[1] == kLowercaseLatinScript) ||
      (subtags.size() > 2 && subtags[2] == kLowercaseLatinScript);
}

Language::~Language() = default;

Language ChooseBestAddressLanguage(const Rule& address_region_rule,
                                   const Language& ui_language) {
  if (address_region_rule.GetLanguages().empty()) {
    return ui_language;
  }

  std::vector<Language> available_languages;
  for (const auto& language_tag : address_region_rule.GetLanguages()) {
    available_languages.emplace_back(language_tag);
  }

  if (ui_language.tag.empty()) {
    return available_languages.front();
  }

  bool has_latin_format = !address_region_rule.GetLatinFormat().empty();

  // The conventionally formatted BCP 47 Latin script with a preceding subtag
  // separator.
  static const char kLatinScriptSuffix[] = "-Latn";
  Language latin_script_language(
      available_languages.front().base + kLatinScriptSuffix);
  if (has_latin_format && ui_language.has_latin_script) {
    return latin_script_language;
  }

  for (const auto& language : available_languages) {
    // Base language comparison works because no region supports the same base
    // language with different scripts, for now. For example, no region supports
    // "zh-Hant" and "zh-Hans" at the same time.
    if (ui_language.base == language.base) {
      return language;
    }
  }

  return has_latin_format ? latin_script_language : available_languages.front();
}

}  // namespace addressinput
}  // namespace i18n