/***************************************************************************//**
 *
 * \file rosa/core/MessageMatcher.hpp
 *
 * \author David Juhasz (david.juhasz@tuwien.ac.at)
 *
 * \date 2017
 *
 * \brief Facilities for checking and matching types of values stored in
 *        `rosa::Message` instances.
 *
 ******************************************************************************/

#ifndef ROSA_CORE_MESSAGEMATCHER_HPP
#define ROSA_CORE_MESSAGEMATCHER_HPP

#include "rosa/core/Message.hpp"

#include <tuple>

namespace rosa {

/// Provides features to type-check a `rosa::Message` instance and extract
/// stored values from it into an `std::tuple` instance with matching type
/// arguments.
///
/// \tparam List `rosa::TypeList` to check the stored values against
template <typename List> struct MessageMatcher;

/// Definition of `rosa::MessageMatcher` for non-empty lists of types, like
/// `rosa::Message` itself.
///
/// \tparam Type first mandatory type
/// \tparam Types any further types
template <typename Type, typename... Types>
struct MessageMatcher<TypeList<Type, Types...>> {

  /// `rosa::Token` associated to the give `rosa::TypeList`.
  static constexpr Token T = TypeToken<Type, Types...>::Value;

  /// Tells if the values stored in a `rosa::Message` instance are matching
  /// types given as `rosa::TypeList<T, Types...>`, considering
  /// `rosa::AtomConstant` instead of `rosa::AtomValue`.
  ///
  /// \param Msg `Message` to match
  ///
  /// \return whether the types of values stored in `Msg` matches
  /// `rosa::TypeList<Type, Types...>`
  static inline bool doesStronglyMatch(const Message &Msg) noexcept;

  /// Gives a `std::tuple` with references to the values stored in a
  /// type-matching instance of `rosa::Message`.
  ///
  /// \param Msg `Message` to extract values from
  ///
  /// \return `tuple` with references to the values stored in `Msg`
  ///
  /// \pre Types of the values stored in `Msg` matches
  /// `rosa::TypeList<Type, Types...>`:\code
  /// doesStronglyMatch(Msg)
  /// \endcode
  static inline std::tuple<const Type &, const Types &...>
  extractedValues(const Message &Msg) noexcept;
};

/// Turns a list of types into a `rosa::TypeList` for `rosa::MessageMatcher`.
template <typename Type, typename...Types>
using MsgMatcher = MessageMatcher<TypeList<Type, Types...>>;

/// Nested namespace with implementation for features of `rosa::MessageMatcher`,
/// consider it private.
namespace {

/// \defgroup MessageMatcherImpl
///
/// An implementation of type-checking and value extraction for
/// `rosa::MessageMatcher`.
///
///@{

/// Template declaration of `rosa::MessageMatcherImpl.
///
/// \tparam List `rosa::TypeList` to match against
template <typename List> struct MessageMatcherImpl;

/// Specialization for `rosa::EmptyTypeList`.
template <> struct MessageMatcherImpl<EmptyTypeList> {
  static inline bool doesStronglyMatchFrom(const Message &Msg,
                                           const size_t Pos) noexcept {
    // Matching EmptyTypeList only if reached the end of the stored types.
    return Pos == Msg.Size;
  }

  static inline std::tuple<> extractedValuesFrom(const Message &Msg,
                                                 const size_t Pos) noexcept {
    // It is valid to extract an empty list only if we reached the end of
    // stored values.
    ASSERT(doesStronglyMatchFrom(Msg, Pos));
    return std::tie();
  }
};

/// Specialization for `rosa::AtomValue` in the head.
template <AtomValue V, typename... Ts>
struct MessageMatcherImpl<TypeList<AtomConstant<V>, Ts...>> {

  static inline bool doesHeadStronglyMatchAt(const Message &Msg,
                                             const size_t Pos) noexcept {
    // Matching an AtomConstant in the head if there is a type stored at Pos,
    // the stored type is AtomValue, and the corresponding value matches the
    // AtomValue V.
    return Pos < Msg.Size && Msg.isTypeAt<AtomValue>(Pos) &&
           Msg.valueAt<AtomValue>(Pos) == V;
  }

  static inline bool doesStronglyMatchFrom(const Message &Msg,
                                           const size_t Pos) noexcept {
    // Matching a non-empty list if the head is matching and the rest of the
    // list is matching.
    return doesHeadStronglyMatchAt(Msg, Pos) &&
           MessageMatcherImpl<TypeList<Ts...>>::doesStronglyMatchFrom(Msg,
                                                                      Pos + 1);
  }

  static inline std::tuple<const AtomConstant<V> &, const Ts &...>
  extractedValuesFrom(const Message &Msg, const size_t Pos) noexcept {
    // Extracting for a non-empty list with a matching AtomConstant in the head
    // by getting the encoded AtomConstant and concatenating it with values
    // extracted for the rest of the list.
    ASSERT(doesHeadStronglyMatchAt(Msg, Pos));
    return std::tuple_cat(
        std::tie(AtomConstant<V>::Value),
        MessageMatcherImpl<TypeList<Ts...>>::extractedValuesFrom(Msg, Pos + 1));
  }

};

/// Definition for the general case when a regular built-in type (not a
/// `rosa::AtomConstant`) is in the head.
template <typename T, typename... Ts>
struct MessageMatcherImpl<TypeList<T, Ts...>> {

  static inline bool doesHeadStronglyMatchAt(const Message &Msg,
                                             const size_t Pos) noexcept {
    // Matching the head if there is a type stored at Pos, and the stored type
    // is T.
    return Pos < Msg.Size && Msg.isTypeAt<T>(Pos);
  }

  static inline bool doesStronglyMatchFrom(const Message &Msg,
                                           const size_t Pos) noexcept {
    // Matching a non-empty list if the head is matching and the rest of the
    // list is matching.
    return doesHeadStronglyMatchAt(Msg, Pos) &&
           MessageMatcherImpl<TypeList<Ts...>>::doesStronglyMatchFrom(Msg,
                                                                      Pos + 1);
  }

  static inline std::tuple<const T &, const Ts &...>
  extractedValuesFrom(const Message &Msg, const size_t Pos) noexcept {
    // Extracting for a non-empty list with a matching head by getting the
    // value for the head and concatenating it with values extracted for the
    // rest of the list.
    ASSERT(doesHeadStronglyMatchAt(Msg, Pos));
    return std::tuple_cat(
        std::tie(Msg.valueAt<T>(Pos)),
        MessageMatcherImpl<TypeList<Ts...>>::extractedValuesFrom(Msg, Pos + 1));
  }
};

///@}

} // End namespace

template <typename Type, typename... Ts>
bool MessageMatcher<TypeList<Type, Ts...>>::doesStronglyMatch(
    const Message &Msg) noexcept {
  // \note Fail quick on T, then match against list with squashed integers the
  // way `rosa::Token` is generated.
  return T == Msg.T &&
         MessageMatcherImpl<typename SquashedTypeList<
             TypeList<Type, Ts...>>::Type>::doesStronglyMatchFrom(Msg, 0);
}

template <typename Type, typename... Ts>
std::tuple<const Type &, const Ts &...>
MessageMatcher<TypeList<Type, Ts...>>::extractedValues(
    const Message &Msg) noexcept {
  ASSERT(doesStronglyMatch(Msg));
  // \note Match against a list with squashed integers as `rosa::Token` is
  // generated.
  return MessageMatcherImpl<typename SquashedTypeList<
      TypeList<Type, Ts...>>::Type>::extractedValuesFrom(Msg, 0);
}

} // End namespace rosa

#endif // ROSA_CORE_MESSAGEMATCHER_HPP