rublon-ssh/PAM/ssh/include/rublon/configuration.hpp

#pragma once

#include <rublon/error.hpp>
#include <rublon/static_string.hpp>
#include <rublon/utils.hpp>
#include <type_traits>

template < typename T >
constexpr bool is_static_string_v = std::is_base_of_v< rublon::details::StaticStringBase, T >;

static_assert(is_static_string_v< rublon::StaticString< 32 > >);

namespace rublon {
class ConfigurationFactory;

enum class FailMode { bypass, deny };

class Configuration {
  public:
    // change to StaticString
    StaticString< 32 > systemToken{};
    StaticString< 32 > secretKey{};
    StaticString< 4096 > apiServer{};

    int prompt{};
    bool enablePasswdEmail{};
    bool logging{};
    bool autopushPrompt{};
    FailMode failMode{};
};

namespace {
    template < class C, typename T >
    T member_ptr_t(T C::*v);

    template < typename T >
    tl::expected< T, ConfigurationError > to(std::string_view);

    template < class T >
    auto to_string(std::string_view arg) -> tl::expected< T, ConfigurationError > {
        T value{};
        assert(arg.size() <= (value.size() - 1));
        std::memcpy(value.data(), arg.data(), arg.size());
        return value;
    }

    template <>
    auto to(std::string_view arg) -> tl::expected< bool, ConfigurationError > {
        return conv::to_bool(arg);
    }
    template <>
    auto to(std::string_view arg) -> tl::expected< int, ConfigurationError > {
        return conv::to_uint32(arg).value_or(0);
    }

    template <>
    auto to(std::string_view arg) -> tl::expected< FailMode, ConfigurationError > {
        if(arg == "bypass")
            return FailMode::bypass;
        if(arg == "deny")
            return FailMode::deny;
        return tl::unexpected{ConfigurationError{ConfigurationError::ErrorClass::BadFailMode}};
    }

    template < typename T >
    auto parse(std::string_view arg) -> tl::expected< T, ConfigurationError > {
        if(arg.empty()) {
            return tl::unexpected{ConfigurationError::ErrorClass::Empty};
        } else {
            if constexpr(is_static_string_v< T >) {
                return to_string< T >(arg);
            } else {
                return to< T >(arg);
            }
        }
    }

} // namespace
struct Entry {
    enum class Source { UserInput, DefaultValue };
    template < auto member >
    static constexpr auto make_read_function() {
        using pType = decltype(member_ptr_t(member));

        return
          [](const Entry * _this, Configuration * configuration, std::string_view userInput) -> tl::expected< Source, ConfigurationError > {
              const auto setDefaultValue = [&](const ConfigurationError & error) -> tl::expected< Source, ConfigurationError > {
                  log(LogLevel::Warning, "applying user provided value for %s parameter, faild with %s", _this->name, error.what());
                  if(_this->defaultValue != nullptr) {
                      configuration->*member = parse< pType >(_this->defaultValue).value();
                      return Source::DefaultValue;
                  } else {
                      log(LogLevel::Error, "parameter %s has not been found and has no default value", _this->name);
                      if(userInput.empty())
                          return tl::unexpected{ConfigurationError::ErrorClass::RequiredValueNotFound};
                      else
                          return tl::unexpected{ConfigurationError::ErrorClass::BadInput};
                  }
              };

              const auto saveValue = [&](const auto & value) -> tl::expected< Source, ConfigurationError > {
                  configuration->*member = value;
                  return Source::UserInput;
              };

              return parse< pType >(userInput).and_then(saveValue).or_else(setDefaultValue);
          };
    }

    const char * name;
    const char * defaultValue;
    tl::expected< Source, ConfigurationError > (*_read)(const Entry * _this, Configuration * configuration, std::string_view userInput);

    bool read(Configuration * configuration, std::optional< std::string_view > userInput) const {
        constexpr const auto emptyString = "";
        const auto logStored             = [&](const auto & source) -> tl::expected< Source, ConfigurationError > {
            rublon::log(LogLevel::Debug,
              "Configuration parameter '%s' was set to '%s'%s",
              this->name,
              this->defaultValue,
              source == Source::DefaultValue ? " (default)" : "");
            return source;
        };

        const auto logError = [&](const auto & error) -> tl::expected< Source, ConfigurationError > {
            rublon::log(LogLevel::Error,
              "Configuration parameter '%s' has no default value and is not provided in user configuraion, aborting",
              this->name);
            return tl::unexpected{error};
        };

        return _read(this, configuration, userInput.value_or(emptyString)).and_then(logStored).or_else(logError).has_value();
    }
};

template < auto member >
constexpr auto make_entry(const char * name, const char * defaultValue) {
    return Entry{name, defaultValue, Entry::make_read_function< member >()};
}

constexpr static inline std::array< Entry, 8 > configurationVariables = { //
  make_entry< &Configuration::logging >("logging", "true"),
  make_entry< &Configuration::systemToken >("systemToken", nullptr),
  make_entry< &Configuration::secretKey >("secretKey", nullptr),
  make_entry< &Configuration::apiServer >("rublonApiServer", nullptr),
  make_entry< &Configuration::prompt >("prompt", "1"),
  make_entry< &Configuration::enablePasswdEmail >("enablePasswdEmail", "true"),
  make_entry< &Configuration::autopushPrompt >("autopushPrompt", "false"),
  make_entry< &Configuration::failMode >("failMode", "deny")};

class ConfigurationFactory {
  public:
    ConfigurationFactory() = default;

    std::optional< Configuration > systemConfig() {
        memory::MonotonicStackResource< 8 * 1024 > stackResource;
        Configuration configuration{};

        std::ifstream file(std::filesystem::path{"/etc/rublon.config"});
        if(not file.good())
            return std::nullopt;

        std::pmr::string line{&stackResource};
        line.reserve(100);
        std::pmr::map< std::pmr::string, std::pmr::string > parameters{&stackResource};

        const auto readParameterByName = [&](std::string_view name) -> std::optional< std::string_view > {
            return parameters.count(name.data()) ? std::optional< std::string_view >{parameters.at(name.data())} : std::nullopt;
        };

        while(std::getline(file, line)) {
            std::pmr::string key{&stackResource};
            std::pmr::string value{&stackResource};

            if(!line.length())
                continue;

            if(line[0] == '#' || line[0] == ';')
                continue;

            auto posEqual = line.find('=');
            key           = line.substr(0, posEqual);
            value         = line.substr(posEqual + 1);

            parameters[std::move(key)] = std::move(value);
        }

        for(const auto & entry : configurationVariables) {
            if(not entry.read(&configuration, readParameterByName(entry.name)))
                return std::nullopt;
        }

        return configuration;
    }
};
} // namespace rublon