// file      : libbutl/optional.mxx -*- C++ -*-
// copyright : Copyright (c) 2014-2018 Code Synthesis Ltd
// license   : MIT; see accompanying LICENSE file

#ifndef __cpp_modules
#pragma once
#endif

// C includes.

#ifndef __cpp_lib_modules
#include <utility>     // move()
#include <functional>  // hash
#include <type_traits> // is_trivially_destructible
#endif

// Other includes.

#ifdef __cpp_modules
export module butl.optional;
#ifdef __cpp_lib_modules
import std.core;
#endif
#endif

#include <libbutl/export.hxx>

LIBBUTL_MODEXPORT namespace butl
{
  // Simple optional class template while waiting for std::optional.
  //
  struct nullopt_t {constexpr explicit nullopt_t (int) {}};
#if defined(__cpp_modules) && defined(__clang__) //@@ MOD Clang duplicate sym.
  inline
#endif
  constexpr nullopt_t nullopt (1);

  namespace details
  {
    template <typename T, bool = std::is_trivially_destructible<T>::value>
    struct optional_data;

    template <typename T>
    struct optional_data<T, false>
    {
      struct empty {};

      union
      {
        empty e_;
        T d_;
      };
      bool v_;

#if !defined(_MSC_VER) || _MSC_VER > 1900
      constexpr optional_data ():           e_ (),              v_ (false) {}
      constexpr optional_data (nullopt_t):  e_ (),              v_ (false) {}
      constexpr optional_data (const T& v): d_ (v),             v_ (true)  {}
      constexpr optional_data (T&& v):      d_ (std::move (v)), v_ (true)  {}
#else
      optional_data ():           e_ (),              v_ (false) {}
      optional_data (nullopt_t):  e_ (),              v_ (false) {}
      optional_data (const T& v): d_ (v),             v_ (true)  {}
      optional_data (T&& v):      d_ (std::move (v)), v_ (true)  {}
#endif

#if (!defined(_MSC_VER) || _MSC_VER > 1900) &&  \
    (!defined(__GNUC__) || __GNUC__ > 4 || defined(__clang__))
      constexpr optional_data (const optional_data& o): v_ (o.v_) {if (v_) new (&d_) T (o.d_);}
      constexpr optional_data (optional_data&& o):      v_ (o.v_) {if (v_) new (&d_) T (std::move (o.d_));}
#else
      optional_data (const optional_data& o): v_ (o.v_) {if (v_) new (&d_) T (o.d_);}
      optional_data (optional_data&& o):      v_ (o.v_) {if (v_) new (&d_) T (std::move (o.d_));}
#endif

      optional_data& operator= (nullopt_t);
      optional_data& operator= (const T&);
      optional_data& operator= (T&&);

      optional_data& operator= (const optional_data&);
      optional_data& operator= (optional_data&&);

      ~optional_data ();
    };

    template <typename T>
    struct optional_data<T, true>
    {
      struct empty {};

      union
      {
        empty e_;
        T d_;
      };
      bool v_;

#if !defined(_MSC_VER) || _MSC_VER > 1900
      constexpr optional_data ():           e_ (),              v_ (false) {}
      constexpr optional_data (nullopt_t):  e_ (),              v_ (false) {}
      constexpr optional_data (const T& v): d_ (v),             v_ (true)  {}
      constexpr optional_data (T&& v):      d_ (std::move (v)), v_ (true)  {}
#else
      optional_data ():           e_ (),              v_ (false) {}
      optional_data (nullopt_t):  e_ (),              v_ (false) {}
      optional_data (const T& v): d_ (v),             v_ (true)  {}
      optional_data (T&& v):      d_ (std::move (v)), v_ (true)  {}
#endif

#if (!defined(_MSC_VER) || _MSC_VER > 1900) && \
    (!defined(__GNUC__) || __GNUC__ > 4 || defined(__clang__))
      constexpr optional_data (const optional_data& o): v_ (o.v_) {if (v_) new (&d_) T (o.d_);}
      constexpr optional_data (optional_data&& o):      v_ (o.v_) {if (v_) new (&d_) T (std::move (o.d_));}
#else
      optional_data (const optional_data& o): v_ (o.v_) {if (v_) new (&d_) T (o.d_);}
      optional_data (optional_data&& o):      v_ (o.v_) {if (v_) new (&d_) T (std::move (o.d_));}
#endif

      optional_data& operator= (nullopt_t);
      optional_data& operator= (const T&);
      optional_data& operator= (T&&);

      optional_data& operator= (const optional_data&);
      optional_data& operator= (optional_data&&);
    };
  }

  template <typename T>
  class optional: private details::optional_data<T>
  {
    using base = details::optional_data<T>;

  public:
    using value_type = T;

#if !defined(_MSC_VER) || _MSC_VER > 1900
    constexpr optional ()                                 {}
    constexpr optional (nullopt_t)                        {}
    constexpr optional (const T& v): base (v)             {}
    constexpr optional (T&& v):      base (std::move (v)) {}
#else
    optional ()                                 {}
    optional (nullopt_t)                        {}
    optional (const T& v): base (v)             {}
    optional (T&& v):      base (std::move (v)) {}
#endif

#if (!defined(_MSC_VER) || _MSC_VER > 1900) &&  \
    (!defined(__GNUC__) || __GNUC__ > 4 || defined(__clang__))
    constexpr optional (const optional&) = default;
    constexpr optional (optional&&)      = default;
#else
    optional (const optional&) = default;
    optional (optional&&)      = default;
#endif

    optional& operator= (nullopt_t v) {static_cast<base&> (*this) = v;             return *this;}
    optional& operator= (const T& v)  {static_cast<base&> (*this) = v;             return *this;}
    optional& operator= (T&& v)       {static_cast<base&> (*this) = std::move (v); return *this;}

    optional& operator= (const optional&) = default;
    optional& operator= (optional&&)      = default;

    T&       value ()       {return this->d_;}
    const T& value () const {return this->d_;}

    T*       operator-> ()       {return &value ();}
    const T* operator-> () const {return &value ();}

    T&       operator* ()       {return value ();}
    const T& operator* () const {return value ();}

    bool         has_value () const {return this->v_;}
    explicit operator bool () const {return this->v_;}
  };

  template <typename T>
  inline auto
  operator== (const optional<T>& x, const optional<T>& y)
  {
    bool px (x), py (y);
    return px == py && (!px || *x == *y);
  }

  template <typename T>
  inline auto
  operator!= (const optional<T>& x, const optional<T>& y)
  {
    return !(x == y);
  }

  template <typename T>
  inline auto
  operator< (const optional<T>& x, const optional<T>& y)
  {
    bool px (x), py (y);
    return px < py || (px && py && *x < *y);
  }

  template <typename T>
  inline auto
  operator> (const optional<T>& x, const optional<T>& y)
  {
    return y < x;
  }
}

namespace std
{
  template <typename T>
  struct hash<butl::optional<T>>: hash<T>
  {
    using argument_type = butl::optional<T>;

    size_t
    operator() (const butl::optional<T>& o) const
      noexcept (noexcept (hash<T> {} (*o)))
    {
      return o ? hash<T>::operator() (*o) : static_cast<size_t> (-3333);
    }
  };
}

#include <libbutl/optional.ixx>