// Boost Lambda Library -- if.hpp ------------------------------------------

// Copyright (C) 1999, 2000 Jaakko Järvi (jaakko.jarvi@cs.utu.fi)
// Copyright (C) 2000 Gary Powell (powellg@amazon.com)
// Copyright (C) 2001-2002 Joel de Guzman
//
// Permission to copy, use, sell and distribute this software is granted
// provided this copyright notice appears in all copies. 
// Permission to modify the code and to distribute modified code is granted
// provided this copyright notice appears in all copies, and a notice 
// that the code was modified is included with the copyright notice.
//
// This software is provided "as is" without express or implied warranty, 
// and with no claim as to its suitability for any purpose.
//
// For more information, see www.boost.org

// --------------------------------------------------------------------------

#if !defined(BOOST_LAMBDA_IF_HPP)
#define BOOST_LAMBDA_IF_HPP

#include "boost/lambda/core.hpp"

// Arithmetic type promotion needed for if_then_else_return
#include "boost/lambda/detail/operator_actions.hpp"
#include "boost/lambda/detail/operator_return_type_traits.hpp"

namespace boost { 
namespace lambda {

// -- if control construct actions ----------------------

class ifthen_action {};
class ifthenelse_action {};
class ifthenelsereturn_action {};

// Specialization for if_then.
template<class Args>
class 
lambda_functor_base<ifthen_action, Args> {
public:
  Args args;
  template <class T> struct sig { typedef void type; };
public:
  explicit lambda_functor_base(const Args& a) : args(a) {}

  template<class RET, CALL_TEMPLATE_ARGS>
  RET call(CALL_FORMAL_ARGS) const {
    if (detail::select(boost::tuples::get<0>(args), CALL_ACTUAL_ARGS)) 
      detail::select(boost::tuples::get<1>(args), CALL_ACTUAL_ARGS); 
  }
};

// If Then
template <class Arg1, class Arg2>
inline const 
lambda_functor<
  lambda_functor_base<
    ifthen_action, 
    tuple<lambda_functor<Arg1>, lambda_functor<Arg2> >
  > 
>
if_then(const lambda_functor<Arg1>& a1, const lambda_functor<Arg2>& a2) {
  return 
    lambda_functor_base<
      ifthen_action, 
      tuple<lambda_functor<Arg1>, lambda_functor<Arg2> > 
    > 
    ( tuple<lambda_functor<Arg1>, lambda_functor<Arg2> >(a1, a2) );
}


// Specialization for if_then_else.
template<class Args>
class 
lambda_functor_base<ifthenelse_action, Args> {
public:
  Args args;
  template <class T> struct sig { typedef void type; };
public:
  explicit lambda_functor_base(const Args& a) : args(a) {}

  template<class RET, CALL_TEMPLATE_ARGS>
  RET call(CALL_FORMAL_ARGS) const {
    if (detail::select(boost::tuples::get<0>(args), CALL_ACTUAL_ARGS)) 
      detail::select(boost::tuples::get<1>(args), CALL_ACTUAL_ARGS); 
    else 
      detail::select(boost::tuples::get<2>(args), CALL_ACTUAL_ARGS);
  }
};



// If then else

template <class Arg1, class Arg2, class Arg3>
inline const 
lambda_functor<
  lambda_functor_base<
    ifthenelse_action, 
    tuple<lambda_functor<Arg1>, lambda_functor<Arg2>, lambda_functor<Arg3> >
  > 
>
if_then_else(const lambda_functor<Arg1>& a1, const lambda_functor<Arg2>& a2, 
             const lambda_functor<Arg3>& a3) {
  return 
    lambda_functor_base<
      ifthenelse_action, 
      tuple<lambda_functor<Arg1>, lambda_functor<Arg2>, lambda_functor<Arg3> >
    > 
    (tuple<lambda_functor<Arg1>, lambda_functor<Arg2>, lambda_functor<Arg3> >
       (a1, a2, a3) );
}

// Our version of operator?:()

template <class Arg1, class Arg2, class Arg3>
inline const 
  lambda_functor<
    lambda_functor_base<
      other_action<ifthenelsereturn_action>, 
      tuple<lambda_functor<Arg1>,
          typename const_copy_argument<Arg2>::type,
          typename const_copy_argument<Arg3>::type>
  > 
>
if_then_else_return(const lambda_functor<Arg1>& a1, 
                    const Arg2 & a2, 
                    const Arg3 & a3) {
  return 
      lambda_functor_base<
        other_action<ifthenelsereturn_action>, 
        tuple<lambda_functor<Arg1>,
              typename const_copy_argument<Arg2>::type,
              typename const_copy_argument<Arg3>::type>
      > ( tuple<lambda_functor<Arg1>,
              typename const_copy_argument<Arg2>::type,
              typename const_copy_argument<Arg3>::type> (a1, a2, a3) );
}

namespace detail {

// return type specialization for conditional expression begins -----------
// start reading below and move upwards

// PHASE 6:1 
// check if A is conbertible to B and B to A
template<int Phase, bool AtoB, bool BtoA, bool SameType, class A, class B>
struct return_type_2_ifthenelsereturn;

// if A can be converted to B and vice versa -> ambiguous
template<int Phase, class A, class B>
struct return_type_2_ifthenelsereturn<Phase, true, true, false, A, B> {
  typedef 
    detail::return_type_deduction_failure<return_type_2_ifthenelsereturn> type;
  // ambiguous type in conditional expression
};
// if A can be converted to B and vice versa and are of same type
template<int Phase, class A, class B>
struct return_type_2_ifthenelsereturn<Phase, true, true, true, A, B> {
  typedef A type;
};


// A can be converted to B
template<int Phase, class A, class B>
struct return_type_2_ifthenelsereturn<Phase, true, false, false, A, B> {
  typedef B type;
};

// B can be converted to A
template<int Phase, class A, class B>
struct return_type_2_ifthenelsereturn<Phase, false, true, false, A, B> {
  typedef A type;
};

// neither can be converted. Then we drop the potential references, and
// try again
template<class A, class B>
struct return_type_2_ifthenelsereturn<1, false, false, false, A, B> {
  // it is safe to add const, since the result will be an rvalue and thus
  // const anyway. The const are needed eg. if the types 
  // are 'const int*' and 'void *'. The remaining type should be 'const void*'
  typedef const typename boost::remove_reference<A>::type plainA; 
  typedef const typename boost::remove_reference<B>::type plainB; 
  // TODO: Add support for volatile ?

  typedef typename
       return_type_2_ifthenelsereturn<
         2,
         boost::is_convertible<plainA,plainB>::value, 
         boost::is_convertible<plainB,plainA>::value,
         boost::is_same<plainA,plainB>::value,
         plainA, 
         plainB>::type type;
};

// PHASE 6:2
template<class A, class B>
struct return_type_2_ifthenelsereturn<2, false, false, false, A, B> {
  typedef 
    detail::return_type_deduction_failure<return_type_2_ifthenelsereturn> type;
  // types_do_not_match_in_conditional_expression 
};



// PHASE 5: now we know that types are not arithmetic.
template<class A, class B>
struct non_numeric_types {
  typedef typename 
    return_type_2_ifthenelsereturn<
      1, // phase 1 
      is_convertible<A,B>::value, 
      is_convertible<B,A>::value, 
      is_same<A,B>::value,
      A, 
      B>::type type;
};

// PHASE 4 : 
// the base case covers arithmetic types with differing promote codes
// use the type deduction of arithmetic_actions
template<int CodeA, int CodeB, class A, class B>
struct arithmetic_or_not {
  typedef typename
    return_type_2<arithmetic_action<plus_action>, A, B>::type type; 
  // plus_action is just a random pick, has to be a concrete instance
};

// this case covers the case of artihmetic types with the same promote codes. 
// non numeric deduction is used since e.g. integral promotion is not 
// performed with operator ?: 
template<int CodeA, class A, class B>
struct arithmetic_or_not<CodeA, CodeA, A, B> {
  typedef typename non_numeric_types<A, B>::type type; 
};

// if either A or B has promote code -1 it is not an arithmetic type
template<class A, class B>
struct arithmetic_or_not <-1, -1, A, B> {
  typedef typename non_numeric_types<A, B>::type type;
};
template<int CodeB, class A, class B>
struct arithmetic_or_not <-1, CodeB, A, B> {
  typedef typename non_numeric_types<A, B>::type type;
};
template<int CodeA, class A, class B>
struct arithmetic_or_not <CodeA, -1, A, B> {
  typedef typename non_numeric_types<A, B>::type type;
};




// PHASE 3 : Are the types same?
// No, check if they are arithmetic or not
template <class A, class B>
struct same_or_not {
  typedef typename detail::remove_reference_and_cv<A>::type plainA;
  typedef typename detail::remove_reference_and_cv<B>::type plainB;

  typedef typename 
    arithmetic_or_not<
      detail::promote_code<plainA>::value, 
      detail::promote_code<plainB>::value, 
      A, 
      B>::type type;
};
// Yes, clear.
template <class A> struct same_or_not<A, A> {
  typedef A type;
};

} // detail

// PHASE 2 : Perform first the potential array_to_pointer conversion 
template<class A, class B>
struct return_type_2<other_action<ifthenelsereturn_action>, A, B> { 

  typedef typename detail::array_to_pointer<A>::type A1;
  typedef typename detail::array_to_pointer<B>::type B1;

  typedef typename 
    boost::add_const<typename detail::same_or_not<A1, B1>::type>::type type;
};

// PHASE 1 : Deduction is based on the second and third operand


// return type specialization for conditional expression ends -----------


// Specialization of lambda_functor_base for if_then_else_return.
template<class Args>
class 
lambda_functor_base<other_action<ifthenelsereturn_action>, Args> {
public:
  Args args;

  template <class SigArgs> struct sig {
  private:
    typedef typename detail::nth_return_type_sig<1, Args, SigArgs>::type ret1;
    typedef typename detail::nth_return_type_sig<2, Args, SigArgs>::type ret2;
  public:
    typedef typename return_type_2<
      other_action<ifthenelsereturn_action>, ret1, ret2
    >::type type;
  };

public:
  explicit lambda_functor_base(const Args& a) : args(a) {}

  template<class RET, CALL_TEMPLATE_ARGS>
  RET call(CALL_FORMAL_ARGS) const {
    return (detail::select(boost::tuples::get<0>(args), CALL_ACTUAL_ARGS)) ?
       detail::select(boost::tuples::get<1>(args), CALL_ACTUAL_ARGS) 
    : 
       detail::select(boost::tuples::get<2>(args), CALL_ACTUAL_ARGS);
  }
};

  // The code below is from Joel de Guzman, some name changes etc. 
  // has been made.

/*=============================================================================

    Copyright (c) 2001-2002 Joel de Guzman

    This software is provided 'as-is', without any express or implied
    warranty. In no event will the copyright holder be held liable for
    any damages arising from the use of this software.

    Permission is granted to anyone to use this software for any purpose,
    including commercial applications, and to alter it and redistribute
    it freely, subject to the following restrictions:

    1.  The origin of this software must not be misrepresented; you must
        not claim that you wrote the original software. If you use this
        software in a product, an acknowledgment in the product documentation
        would be appreciated but is not required.

    2.  Altered source versions must be plainly marked as such, and must
        not be misrepresented as being the original software.

    3.  This notice may not be removed or altered from any source
        distribution.

    URL: http://spirit.sourceforge.net/

==============================================================================*/

///////////////////////////////////////////////////////////////////////////////
//
//  if_then_else_composite
//
//      This composite has two (2) forms:
//
//          if_(condition)
//          [
//              statement
//          ]
//
//      and
//
//          if_(condition)
//          [
//              true_statement
//          ]
//          .else_
//          [
//              false_statement
//          ]
//
//      where condition is an lambda_functor that evaluates to bool. If condition
//      is true, the true_statement (again an lambda_functor) is executed
//      otherwise, the false_statement (another lambda_functor) is executed. The
//      result type of this is void. Note the trailing underscore after
//      if_ and the the leading dot and the trailing underscore before
//      and after .else_.
//
///////////////////////////////////////////////////////////////////////////////
template <typename CondT, typename ThenT, typename ElseT>
struct if_then_else_composite {

    typedef if_then_else_composite<CondT, ThenT, ElseT> self_t;

    template <class SigArgs>
    struct sig { typedef void type; };

    if_then_else_composite(
        CondT const& cond_,
        ThenT const& then_,
        ElseT const& else__)
    :   cond(cond_), then(then_), else_(else__) {}

    template <class Ret, CALL_TEMPLATE_ARGS>
    Ret call(CALL_FORMAL_ARGS) const
    {
        if (cond.internal_call(CALL_ACTUAL_ARGS))
            then.internal_call(CALL_ACTUAL_ARGS);
        else
            else_.internal_call(CALL_ACTUAL_ARGS);
    }

    CondT cond; ThenT then; ElseT else_; //  lambda_functors
};

//////////////////////////////////
template <typename CondT, typename ThenT>
struct else_gen {

    else_gen(CondT const& cond_, ThenT const& then_)
    :   cond(cond_), then(then_) {}

    template <typename ElseT>
    lambda_functor<if_then_else_composite<CondT, ThenT,
        typename as_lambda_functor<ElseT>::type> >
    operator[](ElseT const& else_)
    {
        typedef if_then_else_composite<CondT, ThenT,
            typename as_lambda_functor<ElseT>::type>
        result;

        return result(cond, then, to_lambda_functor(else_));
    }

    CondT cond; ThenT then;
};

//////////////////////////////////
template <typename CondT, typename ThenT>
struct if_then_composite {

    template <class SigArgs>
    struct sig { typedef void type; };

    if_then_composite(CondT const& cond_, ThenT const& then_)
    :   cond(cond_), then(then_), else_(cond, then) {}

    template <class Ret, CALL_TEMPLATE_ARGS>
    Ret call(CALL_FORMAL_ARGS) const
    {
      if (cond.internal_call(CALL_ACTUAL_ARGS))
            then.internal_call(CALL_ACTUAL_ARGS);
    }

    CondT cond; ThenT then; //  lambda_functors
    else_gen<CondT, ThenT> else_;
};

//////////////////////////////////
template <typename CondT>
struct if_gen {

    if_gen(CondT const& cond_)
    :   cond(cond_) {}

    template <typename ThenT>
    lambda_functor<if_then_composite<
        typename as_lambda_functor<CondT>::type,
        typename as_lambda_functor<ThenT>::type> >
    operator[](ThenT const& then) const
    {
        typedef if_then_composite<
            typename as_lambda_functor<CondT>::type,
            typename as_lambda_functor<ThenT>::type>
        result;

        return result(
            to_lambda_functor(cond),
            to_lambda_functor(then));
    }

    CondT cond;
};

//////////////////////////////////
template <typename CondT>
inline if_gen<CondT>
if_(CondT const& cond)
{
    return if_gen<CondT>(cond);
}



} // lambda
} // boost

#endif // BOOST_LAMBDA_IF_HPP


