/***************************************************************************//**
 *
 * \file rosa/core/Message.hpp
 *
 * \author David Juhasz (david.juhasz@tuwien.ac.at)
 *
 * \date 2017
 *
 * \brief Declaration of `rosa::Message` base-class.
 *
 ******************************************************************************/

#ifndef ROSA_CORE_MESSAGE_HPP
#define ROSA_CORE_MESSAGE_HPP

#include "rosa/support/log.h"
#include "rosa/support/type_token.hpp"

#include "rosa/core/forward_declarations.h"

#include <memory>
#include <vector>

namespace rosa {

/// *Message* interface.
///
/// The interface provides means to check the type of the stored values, but
/// actual data is to be managed by derived implementations.
///
/// A `rosa::Message` instance is an immutable data object that obtains its data
/// upon creation and provides only constant references for the stored values.
///
/// \note Any reference obtained from a `rosa::Message` instance remains valid
/// only as long as the owning `rosa::Message` object is not destroyed.
class Message {
protected:
  /// Creates a new instance.
  ///
  /// \note No implementation for empty list.
  ///
  /// \tparam Type type of the mandatory first argument
  /// \tparam Types types of any further arguments
  ///
  /// \note the actual arguments are ignored by the constructor it is only
  /// their type that matters. The actual values are supposed to be handled by
  /// any implementation derived from `rosa::Message`.
  ///
  /// \pre `Type` and `Types` are all built-in types and the number of stored
  /// values does not exceed `rosa::token::MaxTokenizableListSize`.
  template <typename Type, typename... Types>
  Message(const Type &, const Types &...) noexcept;

  /// No copying and moving of `rosa::Message` instances.
  ///@{
  Message(const Message &) = delete;
  Message(Message &&) = delete;
  Message &operator=(const Message &) = delete;
  Message &operator=(Message &&) = delete;
  ///@}

public:
  /// Creates a `rosa::message_t` object from constant lvalue references.
  ///
  /// \tparam Type type of the mandatory first argument
  /// \tparam Types types of any further arguments
  ///
  /// \param T the first value to include in the `rosa::Message`
  /// \param Ts optional further values to include in the `rosa::Message`
  ///
  /// \return new `message_t` object created from the given arguments
  template <typename Type, typename... Types>
  static message_t create(const Type &T, const Types &... Ts) noexcept;

  /// Creates a `rosa::message_t` object from rvalue references.
  ///
  /// \tparam Type type of the mandatory first argument
  /// \tparam Types types of any further arguments
  ///
  /// \param T the first value to include in the `rosa::Message`
  /// \param Ts optional further values to include in the `rosa::Message`
  ///
  /// \return new `message_t` object created from the given arguments
  template <typename Type, typename... Types>
  static message_t create(Type &&T, Types &&... Ts) noexcept;

  /// Represents the types of the values stored in `this` object.
  ///
  /// A valid, non-empty `rosa::Token` representing the types of the values
  /// stored in `this` object.
  const Token T;

  /// The number of values stored in `this` object.
  ///
  /// That is the number of types encoded in `T`.
  const size_t Size;

  /// Destroys `this` object.
  virtual ~Message(void);

  /// Tells if the value stored at a given index is of a given type.
  ///
  /// \note Any `rosa::AtomConstant` is encoded in `rosa::Token` as
  /// the `rosa::AtomValue` wrapped into it.
  ///
  /// \tparam Type type to match against
  ///
  /// \param Pos index the type of the value at is to be matched against `Type`
  ///
  /// \return if the value at index `Pos` of type `Type`
  ///
  /// \pre `Pos` is a valid index:\code
  /// Pos < Size
  /// \endcode
  template <typename Type> bool isTypeAt(const size_t Pos) const noexcept;

  /// Gives a constant reference of a value of a given type stored at a given
  /// index.
  ///
  /// \tparam Type type to give a reference of
  ///
  /// \param Pos index to set the reference for
  ///
  /// \return constant reference of `Type` for the value stored at index `Pos`
  ///
  /// \pre `Pos` is a valid index and the value at index `Pos` is of type
  /// `Type`:\code
  /// Pos < Size && isTypeAt(Pos)
  /// \endcode
  template <typename Type> const Type &valueAt(const size_t Pos) const noexcept;

protected:
  /// Provides an untyped pointer for the value at a given index.
  ///
  /// \param Pos index to take a pointer for
  ///
  /// \return untyped pointer for the value stored at index `Pos`
  ///
  /// \pre `Pos` is a valid index:\code
  /// Pos < Size
  /// \endcode
  virtual const void *pointerTo(const size_t Pos) const noexcept = 0;
};

/// Nested namespace with implementation for `rosa::Message`, consider it
/// private.
namespace {

/// Template class for an implementation of `rosa::Message`.
///
/// \tparam Types types whose values are to be stored
template <typename... Types> class LocalMessage;

/// Initializes a pre-allocated memory area with values from constant lvalue
/// references.
///
/// \tparam Types types whose values are to be stored
///
/// \param Arena pre-allocated memory area to store values to
/// \param Ts the values to store in `Arena`
///
/// \note `Arena` needs to be a valid pointer to a memory area big enough for
/// values of `Types`.
template <typename... Types>
inline void createMessageElements(void *const Arena,
                                  const Types &... Ts) noexcept;

/// \defgroup createMessageElement from const lvalue references
///
/// Stores values from constant lvalue references into a pre-allocated memory
/// area.
///
/// \note To be used by the implementation of `rosa::createMessageElements`.
///
/// \todo Document these functions.
///@{

/// \note This terminal case is used for both constant lvalue references and
/// value references.
template <size_t Pos>
inline void createMessageElement(void *const,
                                 const std::vector<size_t> &Offsets) {
  ASSERT(Pos == Offsets.size());
}

template <size_t Pos, typename Type, typename... Types>
inline void createMessageElement(void *const Arena,
                                 const std::vector<size_t> &Offsets,
                                 const Type &T, const Types &... Ts) noexcept {
  ASSERT(Arena != nullptr && Pos < Offsets.size());
  new (static_cast<Type *>(static_cast<void *>(static_cast<uint8_t *>(Arena) +
                                               Offsets[Pos]))) Type(T);
  createMessageElement<Pos + 1>(Arena, Offsets, Ts...);
}

template <size_t Pos, AtomValue V, typename... Types>
inline void
createMessageElement(void *const Arena, const std::vector<size_t> &Offsets,
                     const AtomConstant<V> &, const Types &... Ts) noexcept {
  ASSERT(Arena != nullptr && Pos < Offsets.size());
  *static_cast<AtomValue *>(
      static_cast<void *>(static_cast<uint8_t *>(Arena) + Offsets[Pos])) = V;
  createMessageElement<Pos + 1>(Arena, Offsets, Ts...);
}

///@}

/// Implementation of the template.
///
/// \tparam Type the type of the mandatory first value to store
/// \tparam Types types of any further values to store
///
/// \param Arena pre-allocated memory area to store values to
/// \param T the first value to store in `Arena`˛
/// \param Ts optional further values to store in `Arena`
///
/// \pre `Arena` is not `nullptr`.
template <typename Type, typename... Types>
inline void createMessageElements(void *const Arena, const Type &T,
                                  const Types &... Ts) noexcept {
  ASSERT(Arena != nullptr);
  createMessageElement<0>(Arena, LocalMessage<Type, Types...>::Offsets, T,
                          Ts...);
}

/// Initializes a pre-allocated memory area with values from rvalue references.
///
/// \tparam Types types whose values are to be stored
///
/// \param Arena pre-allocated memory area to store values to
/// \param Ts the values to store in `Arena`
///
/// \note `Arena` needs to be a valid pointer to a memory area big enough for
/// values of `Types`.
template <typename... Types>
inline void createMessageElements(void *const Arena, Types &&... Ts) noexcept;

/// \defgroup createMessageElement from rvalue references
///
/// Stores values from rvalue references into a pre-allocated memory area.
///
/// \note To be used by the implementation of `rosa::createMessageElements`.
///
/// \todo Document these functions.
///@{

template <size_t Pos, typename Type, typename... Types>
inline void createMessageElement(void *const Arena,
                                 const std::vector<size_t> &Offsets, Type &&T,
                                 Types &&... Ts) noexcept {
  ASSERT(Arena != nullptr && Pos < Offsets.size());
  new (static_cast<Type *>(static_cast<void *>(
      static_cast<uint8_t *>(Arena) + Offsets[Pos]))) Type(std::move(T));
  createMessageElement<Pos + 1>(Arena, Offsets, std::move(Ts)...);
}

template <size_t Pos, AtomValue V, typename... Types>
inline void createMessageElement(void *const Arena,
                                 const std::vector<size_t> &Offsets,
                                 AtomConstant<V> &&, Types &&... Ts) noexcept {
  ASSERT(Arena != nullptr && Pos < Offsets.size());
  *static_cast<AtomValue *>(
      static_cast<void *>(static_cast<uint8_t *>(Arena) + Offsets[Pos])) = V;
  createMessageElement<Pos + 1>(Arena, Offsets, std::move(Ts)...);
}

///@}

/// Implementation of the template.
///
/// \tparam Type the type of the mandatory first value to store
/// \tparam Types types of any further values to store
///
/// \param Arena pre-allocated memory area to store values to
/// \param T the first value to store in `Arena`˛
/// \param Ts optional further values to store in `Arena`
///
/// \pre `Arena` is not `nullptr`.
template <typename Type, typename... Types>
inline void createMessageElements(void *const Arena, Type &&T,
                                  Types &&... Ts) noexcept {
  ASSERT(Arena != nullptr);
  createMessageElement<0>(Arena, LocalMessage<Type, Types...>::Offsets,
                          std::move(T), std::move(Ts)...);
}

/// Destroys values allocated by `rosa::createMessageElements`.
///
/// \tparam Type type of the mandatory first value stored in `Arena`
/// \tparam Types futher types whose values are stored in `Arena`
///
/// \param Arena the memory area to destroy values from
///
/// \note Arena needs to be a valid pointer to a memory area where values of
/// `Types` are stored.
template <typename Type, typename... Types>
inline void destroyMessageElements(void *const Arena) noexcept;

/// \defgroup destroyMessageElement
///
/// Destroys values from a memory area.
///
/// \note To be used by the implementation of `rosa::destroyMessageElements`.
///
/// \todo Document these functions.
///@{

template <size_t Pos>
inline void destroyMessageElement(void *const,
                                  const std::vector<size_t> &Offsets) noexcept {
  ASSERT(Pos == Offsets.size());
}

template <size_t Pos, typename Type, typename... Types>
inline void destroyMessageElement(void *const Arena,
                                  const std::vector<size_t> &Offsets) noexcept {
  ASSERT(Arena != nullptr && Pos < Offsets.size());
  static_cast<Type *>(
      static_cast<void *>(static_cast<uint8_t *>(Arena) + Offsets[Pos]))
      ->~Type();
  destroyMessageElement<Pos + 1, Types...>(Arena, Offsets);
}

///@}

/// Implementation of the template.
///
/// \tparam Type the type of the mandatory first value to destroy
/// \tparam Types types of any further values to destroy
///
/// \param Arena the memory area to destroy values from
///
/// \pre `Arena` is not `nullptr`.
template <typename Type, typename... Types>
inline void destroyMessageElements(void *const Arena) noexcept {
  ASSERT(Arena != nullptr);
  destroyMessageElement<0, Type, Types...>(
      Arena, LocalMessage<Type, Types...>::Offsets);
}

/// Implementation of the template `rosa::LocalMessage` providing facilities for
/// storing values as a `rosa::Message` object.
///
/// \tparam Type type of the first mandatory value of the `Message`
/// \tparam Types of any further values
template <typename Type, typename... Types>
class LocalMessage<Type, Types...> : public Message {
public:
  /// `rosa::Token` for the stored values.
  ///
  /// \note Only for compile-time checks! This static member is not defined
  /// because it must be the same as `rosa::Message::T`.
  static constexpr Token ST =
      TypeToken<typename std::decay<Type>::type,
                typename std::decay<Types>::type...>::Value;

  /// Byte offsets to access stored values in `Arena`.
  static const std::vector<size_t> Offsets;

private:
  /// A BLOB storing all the values one after the other.
  void *const Arena;

  /// Generates byte offsets for accessing values stored in `Arena`.
  ///
  /// \return `std::vector` containing byte offsets for accessing values stored
  /// in `Arena`
  static std::vector<size_t> offsets(void) noexcept {
    Token T = ST;                            // Need a mutable copy.
    size_t I = 0;                            // Start indexing from position 0.
    std::vector<size_t> O(lengthOfToken(T)); // Allocate vector of proper size.
    O[0] = 0;                                // First offset is always 0.
    while (!emptyToken(T)) {
      ASSERT(I < O.size());
      // Calculate next offset based on the previous one.
      O[I + 1] = O[I] + sizeOfHeadOfToken(T);
      dropHeadOfToken(T), ++I;
    }
    ASSERT(I == O.size());
    return O;
  }

public:
  /// Creates an instance from constant lvalue references.
  ///
  /// \param T the mandatory first value to store in the `rosa::Message` object
  /// \param Ts optional further values to store in the `rosa::Message` object
  LocalMessage(const Type &T, const Types &... Ts) noexcept
      : Message(T, Ts...),
        Arena(::operator new(sizeOfValuesOfToken(ST))) {
    ASSERT(this->T == ST && Size == Offsets.size() &&
           Arena != nullptr); // Sanity check.
    createMessageElements(Arena, T, Ts...);
  }

  /// Creates an instance from rvalue references.
  ///
  /// \param T the mandatory first value to store in the `rosa::Message` object
  /// \param Ts optional further values to store in the `rosa::Message` object
  LocalMessage(Type &&T, Types &&... Ts) noexcept
      : Message(T, Ts...),
        Arena(::operator new(sizeOfValuesOfToken(ST))) {
    ASSERT(this->T == ST && Size == Offsets.size() &&
           Arena != nullptr); // Sanity check.
    createMessageElements(Arena, std::move(T), std::move(Ts)...);
  }

  // Destroys `this` object.
  ~LocalMessage(void) {
    destroyMessageElements<Type, Types...>(Arena);
    ::operator delete(Arena);
  }

  /// Provides an untyped pointer for the constant value stored at a position.
  ///
  /// \param Pos the index of the value to return an untyped pointer for
  ///
  /// \return untyped pointer for the constant value stored at index `Pos`
  const void *pointerTo(const size_t Pos) const noexcept override {
    ASSERT(Pos < Offsets.size());
    return static_cast<uint8_t *>(Arena) + Offsets[Pos];
  }
};

// Implementation of the static member field `rosa::LocalMessage::Offsets`.
template <typename Type, typename... Types>
const std::vector<size_t> LocalMessage<Type, Types...>::Offsets =
    LocalMessage<Type, Types...>::offsets();

} // End namespace

template <typename Type, typename... Types>
Message::Message(const Type &, const Types &...) noexcept
    : T(TypeToken<typename std::decay<Type>::type,
                  typename std::decay<Types>::type...>::Value),
      Size(lengthOfToken(T)) {
  ASSERT(validToken(T) &&
         lengthOfToken(T) == (1 + sizeof...(Types))); // Sanity check.
  LOG_TRACE("Creating Message with Token(" + to_string(T) + ")");
}

/// \note The implementation instantiates a private local template class
/// `LocalMessage`.
template <typename Type, typename... Types>
message_t Message::create(const Type &T, const Types &... Ts) noexcept {
  return message_t(new LocalMessage<Type, Types...>(T, Ts...));
}

/// \note The implementation instantiates a private local template class
/// `LocalMessage`.
template <typename Type, typename... Types>
message_t Message::create(Type &&T, Types &&... Ts) noexcept {
  return message_t(
      new LocalMessage<Type, Types...>(std::move(T), std::move(Ts)...));
}

template <typename Type>
bool Message::isTypeAt(const size_t Pos) const noexcept {
  ASSERT(Pos < Size);
  Token T_ = T; // NOLINT
  dropNOfToken(T_, Pos);
  return isHeadOfTokenTheSameType<Type>(T_);
}

template <typename Type>
const Type &Message::valueAt(const size_t Pos) const noexcept {
  ASSERT(Pos < Size && isTypeAt<Type>(Pos));
  return *static_cast<const Type *>(pointerTo(Pos));
}

} // End namespace rosa

#endif // ROSA_CORE_MESSAGE_HPP