// Copyright (c) 2005-2008  INRIA Sophia-Antipolis (France).
// All rights reserved.
//
// This file is part of CGAL (www.cgal.org)
//
// $URL: https://github.com/CGAL/cgal/blob/v5.1/STL_Extension/include/CGAL/Uncertain.h $
// $Id: Uncertain.h 3302086 2020-06-13T23:41:39+05:30 Abhay Raj Singh
// SPDX-License-Identifier: LGPL-3.0-or-later OR LicenseRef-Commercial
//
// Author(s)     : Sylvain Pion

#ifndef CGAL_UNCERTAIN_H
#define CGAL_UNCERTAIN_H

#include <CGAL/config.h>
#include <CGAL/assertions.h>
#include <CGAL/enum.h>
#include <CGAL/Profile_counter.h>
#include <stdexcept>
#include <typeinfo>

namespace CGAL {

namespace internal {

  // Accessory traits class to provide min and max value of a type.
  // Specialized for bool and CGAL's enums.
  template < typename T >
  struct Minmax_traits;

  template <>
  struct Minmax_traits <bool>
  {
    static const bool min = false;
    static const bool max = true;
  };

  template <>
  struct Minmax_traits <Sign>
  {
    static const Sign min = NEGATIVE;
    static const Sign max = POSITIVE;
  };

  template <>
  struct Minmax_traits <Bounded_side>
  {
    static const Bounded_side min = ON_UNBOUNDED_SIDE;
    static const Bounded_side max = ON_BOUNDED_SIDE;
  };

  template <>
  struct Minmax_traits <Angle>
  {
    static const Angle min = OBTUSE;
    static const Angle max = ACUTE;
  };

} // namespace internal


// Exception type for the automatic conversion.
class Uncertain_conversion_exception
  : public std::range_error
{
public:
  Uncertain_conversion_exception(const std::string &s)
    : std::range_error(s) {}
};


// Encodes a range [inf,sup] of values of type T.
// T can be enums or bool.

template < typename T >
class Uncertain
{
  T _i, _s;

public:

  typedef T  value_type;

  typedef CGAL::Uncertain_conversion_exception  Uncertain_conversion_exception;

  Uncertain()
    : _i(), _s() {}

  Uncertain(T t)
    : _i(t), _s(t) {}

  Uncertain(T i, T s)
    : _i(i), _s(s) { CGAL_precondition(i <= s); }

  Uncertain& operator=(T t)
  {
    _i = _s = t;
    return *this;
  }

  T inf() const { return _i; }
  T sup() const { return _s; }

  bool is_same(Uncertain u) const { return _i == u._i && _s == u._s; }

  bool is_certain() const { return _i == _s; }

  T make_certain() const
  {
    if (is_certain())
      return _i;
    CGAL_PROFILER(std::string("Uncertain_conversion_exception thrown for CGAL::Uncertain< ")
                  + typeid(T).name() + " >");
    throw Uncertain_conversion_exception(
                  "Undecidable conversion of CGAL::Uncertain<T>");
  }

#ifndef CGAL_NO_UNCERTAIN_CONVERSION_OPERATOR
  // NB : the general conversion to bool might be too risky.
  //      boost::tribool uses a more restricted conversion (see below).
  operator T() const
  {
    return make_certain();
  }
#else
private:
  struct dummy {
    void nonnull() {};
  };

  typedef void (dummy::*safe_bool)();

public:
  operator safe_bool() const
  {
    return make_certain() ? &dummy::nonnull : 0;
  }
#endif

  static Uncertain indeterminate();
};


// Access functions
// ----------------

template < typename T >
inline
T inf(Uncertain<T> i)
{
  return i.inf();
}

template < typename T >
inline
T sup(Uncertain<T> i)
{
  return i.sup();
}


// Basic functions
// ---------------

#if 1
// Commenting them out allows the test-suite to spot those predicates that do not
// propagate Uncertain-ty correctly.  But they should probably be enabled
// for now, for backward-compatibility.
template < typename T >
inline
bool is_certain(T)
{
  return true;
}

template < typename T >
inline
T get_certain(T t)
{
  return t;
}
#endif

template < typename T >
inline
bool is_certain(Uncertain<T> a)
{
  return a.is_certain();
}

template < typename T >
inline
T get_certain(Uncertain<T> a)
{
  CGAL_assertion(is_certain(a));
  return a.inf();
}

template < typename T >
inline
Uncertain<T>
Uncertain<T>::indeterminate()
{
  return Uncertain<T>(internal::Minmax_traits<T>::min, internal::Minmax_traits<T>::max);
}

namespace internal {

        // helper class
        template < typename T >
        struct Indeterminate_helper {
                typedef T result_type;
                result_type operator()() const
                { return T(); }
        };

        template < typename T >
        struct Indeterminate_helper< Uncertain<T> > {
                typedef Uncertain<T> result_type;
                result_type operator()() const
                { return Uncertain<T>::indeterminate(); }
        };

} // namespace internal

template < typename T >
inline
typename internal::Indeterminate_helper<T>::result_type
indeterminate()
{
  return internal::Indeterminate_helper<T>()();
}

template < typename T >
inline
bool is_indeterminate(T)
{
  return false;
}

template < typename T >
inline
bool is_indeterminate(Uncertain<T> a)
{
  return ! a.is_certain();
}


// certainly/possibly
// ------------------

inline bool certainly(bool b) { return b; }
inline bool possibly(bool b) { return b; }

inline bool certainly_not(bool b) { return !b; }
inline bool possibly_not(bool b) { return !b; }

inline
bool certainly(Uncertain<bool> c)
{
  return is_certain(c) && get_certain(c);
}

inline
bool possibly(Uncertain<bool> c)
{
  return !is_certain(c) || get_certain(c);
}

inline
bool certainly_not(Uncertain<bool> c)
{
  return is_certain(c) && !get_certain(c);
}

inline
bool possibly_not(Uncertain<bool> c)
{
  return !is_certain(c) || !get_certain(c);
}


// Boolean operations for Uncertain<bool>
// --------------------------------------

inline
Uncertain<bool> operator!(Uncertain<bool> a)
{
  return Uncertain<bool>(!a.sup(), !a.inf());
}

inline
Uncertain<bool> operator|(Uncertain<bool> a, Uncertain<bool> b)
{
  return Uncertain<bool>(a.inf() | b.inf(), a.sup() | b.sup());
}

inline
Uncertain<bool> operator|(bool a, Uncertain<bool> b)
{
  return Uncertain<bool>(a | b.inf(), a | b.sup());
}

inline
Uncertain<bool> operator|(Uncertain<bool> a, bool b)
{
  return Uncertain<bool>(a.inf() | b, a.sup() | b);
}

inline
Uncertain<bool> operator&(Uncertain<bool> a, Uncertain<bool> b)
{
  return Uncertain<bool>(a.inf() & b.inf(), a.sup() & b.sup());
}

inline
Uncertain<bool> operator&(bool a, Uncertain<bool> b)
{
  return Uncertain<bool>(a & b.inf(), a & b.sup());
}

inline
Uncertain<bool> operator&(Uncertain<bool> a, bool b)
{
  return Uncertain<bool>(a.inf() & b, a.sup() & b);
}

// operator&& and operator|| are not provided because, unless their bool counterpart,
// they lack the "short-circuiting" property.
// We provide macros CGAL_AND and CGAL_OR, which attempt to emulate their behavior.
// Key things : do not evaluate expressions twice, and evaluate the right hand side
// expression only when needed.
// TODO : C++0x lambdas should be able to help here.
#ifdef CGAL_CFG_NO_STATEMENT_EXPRESSIONS
#  define CGAL_AND(X, Y)  ((X) && (Y))
#  define CGAL_OR(X, Y)   ((X) || (Y))
#else
#  define CGAL_AND(X, Y) \
       __extension__ \
       ({ CGAL::Uncertain<bool> CGAL_TMP = (X); \
          CGAL::certainly_not(CGAL_TMP) ? CGAL::make_uncertain(false) \
                                        : CGAL_TMP & CGAL::make_uncertain((Y)); })
#  define CGAL_OR(X, Y) \
       __extension__ \
       ({ CGAL::Uncertain<bool> CGAL_TMP = (X); \
          CGAL::certainly(CGAL_TMP) ? CGAL::make_uncertain(true) \
                                    : CGAL_TMP | CGAL::make_uncertain((Y)); })
#endif

#define CGAL_AND_3(X, Y, Z)  CGAL_AND(X, CGAL_AND(Y, Z))
#define CGAL_OR_3(X, Y, Z)   CGAL_OR(X, CGAL_OR(Y, Z))


// Equality operators

template < typename T >
inline
Uncertain<bool> operator==(Uncertain<T> a, Uncertain<T> b)
{
  if (a.sup() < b.inf() || b.sup() < a.inf())
    return false;
  if (is_certain(a) && is_certain(b)) // test above implies get_certain(a) == get_certain(b)
    return true;
  return Uncertain<bool>::indeterminate();
}

template < typename T >
inline
Uncertain<bool> operator==(Uncertain<T> a, T b)
{
  if (a.sup() < b || b < a.inf())
    return false;
  if (is_certain(a))
    return true;
  return Uncertain<bool>::indeterminate();
}

template < typename T >
inline
Uncertain<bool> operator==(T a, Uncertain<T> b)
{
  return b == a;
}

template < typename T >
inline
Uncertain<bool> operator!=(Uncertain<T> a, Uncertain<T> b)
{
  return ! (a == b);
}

template < typename T >
inline
Uncertain<bool> operator!=(Uncertain<T> a, T b)
{
  return ! (a == b);
}

template < typename T >
inline
Uncertain<bool> operator!=(T a, Uncertain<T> b)
{
  return ! (a == b);
}


// Comparison operators (useful for enums only, I guess (?) ).

template < typename T >
inline
Uncertain<bool> operator<(Uncertain<T> a, Uncertain<T> b)
{
  if (a.sup() < b.inf())
    return true;
  if (a.inf() >= b.sup())
    return false;
  return Uncertain<bool>::indeterminate();
}

template < typename T >
inline
Uncertain<bool> operator<(Uncertain<T> a, T b)
{
  if (a.sup() < b)
    return true;
  if (a.inf() >= b)
    return false;
  return Uncertain<bool>::indeterminate();
}

template < typename T >
inline
Uncertain<bool> operator<(T a, Uncertain<T> b)
{
  if (a < b.inf())
    return true;
  if (a >= b.sup())
    return false;
  return Uncertain<bool>::indeterminate();
}

template < typename T >
inline
Uncertain<bool> operator>(Uncertain<T> a, Uncertain<T> b)
{
  return b < a;
}

template < typename T >
inline
Uncertain<bool> operator>(Uncertain<T> a, T b)
{
  return b < a;
}

template < typename T >
inline
Uncertain<bool> operator>(T a, Uncertain<T> b)
{
  return b < a;
}

template < typename T >
inline
Uncertain<bool> operator<=(Uncertain<T> a, Uncertain<T> b)
{
  return !(b < a);
}

template < typename T >
inline
Uncertain<bool> operator<=(Uncertain<T> a, T b)
{
  return !(b < a);
}

template < typename T >
inline
Uncertain<bool> operator<=(T a, Uncertain<T> b)
{
  return !(b < a);
}

template < typename T >
inline
Uncertain<bool> operator>=(Uncertain<T> a, Uncertain<T> b)
{
  return !(a < b);
}

template < typename T >
inline
Uncertain<bool> operator>=(Uncertain<T> a, T b)
{
  return !(a < b);
}

template < typename T >
inline
Uncertain<bool> operator>=(T a, Uncertain<T> b)
{
  return !(a < b);
}


// Maker function (a la std::make_pair).

template < typename T >
inline
Uncertain<T> make_uncertain(T t)
{
  return Uncertain<T>(t);
}

template < typename T >
inline
Uncertain<T> make_uncertain(Uncertain<T> t)
{
  return t;
}


// make_certain() : Forcing a cast to certain (possibly throwing).
// This is meant to be used only in cases where we cannot easily propagate the
// uncertainty, such as when used in a switch statement (code may later be
// revisited to do things in a better way).

template < typename T >
inline
T make_certain(T t)
{
  return t;
}

template < typename T >
inline
T make_certain(Uncertain<T> t)
{
  return t.make_certain();
}


// opposite
template < typename T > // should be constrained only for enums.
inline
Uncertain<T> operator-(Uncertain<T> u)
{
  return Uncertain<T>(-u.sup(), -u.inf());
}

// "sign" multiplication.
// Should be constrained only for "sign" enums, useless for bool.
template < typename T >
Uncertain<T> operator*(Uncertain<T> a, Uncertain<T> b)
{
  if (a.inf() >= 0)                                   // e>=0
  {
    // b>=0     [a.inf()*b.inf(); a.sup()*b.sup()]
    // b<=0     [a.sup()*b.inf(); a.inf()*b.sup()]
    // b~=0     [a.sup()*b.inf(); a.sup()*b.sup()]
    T aa = a.inf(), bb = a.sup();
    if (b.inf() < 0)
    {
        aa = bb;
        if (b.sup() < 0)
            bb = a.inf();
    }
    return Uncertain<T>(aa * b.inf(), bb * b.sup());
  }
  else if (a.sup()<=0)                                // e<=0
  {
    // b>=0     [a.inf()*b.sup(); a.sup()*b.inf()]
    // b<=0     [a.sup()*b.sup(); a.inf()*b.inf()]
    // b~=0     [a.inf()*b.sup(); a.inf()*b.inf()]
    T aa = a.sup(), bb = a.inf();
    if (b.inf() < 0)
    {
        aa=bb;
        if (b.sup() < 0)
            bb=a.sup();
    }
    return Uncertain<T>(bb * b.sup(), aa * b.inf());
  }
  else                                          // 0 \in [inf();sup()]
  {
    if (b.inf()>=0)                           // d>=0
      return Uncertain<T>(a.inf() * b.sup(), a.sup() * b.sup());
    if (b.sup()<=0)                           // d<=0
      return Uncertain<T>(a.sup() * b.inf(), a.inf() * b.inf());
                                                // 0 \in d
    T tmp1 = a.inf() * b.sup();
    T tmp2 = a.sup() * b.inf();
    T tmp3 = a.inf() * b.inf();
    T tmp4 = a.sup() * b.sup();
    return Uncertain<T>((std::min)(tmp1, tmp2), (std::max)(tmp3, tmp4));
  }
}

template < typename T >
inline
Uncertain<T> operator*(T a, Uncertain<T> b)
{
        return Uncertain<T>(a) * b;
}

template < typename T >
inline
Uncertain<T> operator*(Uncertain<T> a, T b)
{
        return a * Uncertain<T>(b);
}

// enum_cast overload

#ifdef CGAL_CFG_MATCHING_BUG_5

template < typename T, typename U >
inline
Uncertain<T> enum_cast_bug(Uncertain<U> u, const T*)
{
  return Uncertain<T>(static_cast<const T>(u.inf()),
                      static_cast<const T>(u.sup()));
}

#else

template < typename T, typename U >
inline
Uncertain<T> enum_cast(Uncertain<U> u)
{
  return Uncertain<T>(static_cast<T>(u.inf()), static_cast<T>(u.sup()));
}

#endif

} //namespace CGAL

#endif // CGAL_UNCERTAIN_H