//          Copyright Joakim Karlsson & Kim Gräsman 2010-2012.
// Distributed under the Boost Software License, Version 1.0.
//    (See accompanying file LICENSE_1_0.txt or copy at
//          http://www.boost.org/LICENSE_1_0.txt)

#ifndef IGLOO_CONSTRAINT_H
#define IGLOO_CONSTRAINT_H

namespace snowhouse {
  
  struct ConstraintOperator;
  typedef std::stack<bool> ResultStack;
  typedef std::stack<ConstraintOperator*> OperatorStack;

  template <typename HT, typename TT>
  struct ConstraintList
  {
    typedef HT HeadType;
    typedef TT TailType;
    
    ConstraintList(const HeadType& head, const TailType& tail) 
    : m_head(head), m_tail(tail)
    {
    }
    
    HeadType m_head;
    TailType m_tail;
  };
  
  struct Nil 
  {
    Nil() {}
    Nil(const Nil&) {}
  };
  

  // ---- These structs defines the resulting types of list concatenation operations
  template <typename L1, typename L2> 
  struct type_concat 
  {
    typedef ConstraintList<typename L1::HeadType, typename type_concat<typename L1::TailType, L2>::t> t;
  };
  
  template <typename L2> struct type_concat<Nil, L2> { typedef L2 t; };
  
  template <typename L3> inline L3 tr_concat(const Nil&, const Nil&) { return Nil(); }    
  
  
  // ---- These structs define the concatenation operations.
  
  template <typename LeftList, typename RightList, typename ResultList>
  struct ListConcat
  {
    static ResultList Concatenate(const LeftList& left, const RightList& right)
    {
      return ResultList(left.m_head, ListConcat<typename LeftList::TailType, RightList, typename type_concat< typename LeftList::TailType, RightList>::t>::Concatenate(left.m_tail, right));
    }
  };
  
  // Concatenating an empty list with a second list yields the second list
  template <typename RightList, typename ResultList>
  struct ListConcat<Nil, RightList, ResultList>
  {
    static ResultList Concatenate(const Nil&, const RightList& right)
    {
      return right;
    }
    
  };
   
  // Concatenating two empty lists yields an empty list
  template <typename ResultList>
  struct ListConcat<Nil, Nil, ResultList>
  {
    static ResultList Concatenate(const Nil&, const Nil&)
    {
      return Nil();
    }
  }; 
  
  // ---- The concatenation operation
  
  template <typename L1, typename L2>
  inline typename type_concat<L1, L2>::t Concatenate(const L1& list1, const L2& list2)
  {
    return ListConcat<L1, L2, typename type_concat<L1, L2>::t>::Concatenate(list1, list2);
  }
}

#endif