/*******************************************************************************
 *
 * TRIQS: a Toolbox for Research in Interacting Quantum Systems
 *
 * Copyright (C) 2012 by M. Ferrero, O. Parcollet
 *
 * TRIQS is free software: you can redistribute it and/or modify it under the
 * terms of the GNU General Public License as published by the Free Software
 * Foundation, either version 3 of the License, or (at your option) any later
 * version.
 *
 * TRIQS is distributed in the hope that it will be useful, but WITHOUT ANY
 * WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
 * FOR A PARTICULAR PURPOSE. See the GNU General Public License for more
 * details.
 *
 * You should have received a copy of the GNU General Public License along with
 * TRIQS. If not, see <http://www.gnu.org/licenses/>.
 *
 ******************************************************************************/
#ifndef TRIQS_GF_EXPR_H
#define TRIQS_GF_EXPR_H
#include <triqs/utility/expression_template_tools.hpp>
namespace triqs { namespace gfs {

 using utility::is_in_ZRC;
 using utility::remove_rvalue_ref;

 namespace gfs_expr_tools {

  // a wrapper for scalars 
  template<typename S> struct scalar_wrap {
   typedef void variable_t;
   typedef void target_t;
   typedef void option_t;
   S s; 
   template<typename T> scalar_wrap(T && x):s(std::forward<T>(x)){}  
   S singularity() const { return s;}
   template<typename KeyType> S operator[](KeyType && key) const { return s;}
   template<typename ... Args> inline S operator()(Args && ... args) const { return s;}
   friend std::ostream &operator <<(std::ostream &sout, scalar_wrap const &expr){return sout << expr.s; }
  };

  // Combine the two meshes of LHS and RHS : need to specialize where there is a scalar
  struct combine_mesh {
   template<typename L, typename R> 
    auto operator() (L && l, R && r) const -> decltype(std::forward<L>(l).mesh()) { 
     if (!(l.mesh() == r.mesh())) TRIQS_RUNTIME_ERROR << "Mesh mismatch : ";//<< l.mesh()<<" vs" <<r.mesh();
     return std::forward<L>(l).mesh();
    }
   template<typename S, typename R> auto operator() (scalar_wrap<S> const &, R && r) const DECL_AND_RETURN(std::forward<R>(r).mesh());
   template<typename S, typename L> auto operator() (L && l, scalar_wrap<S> const &) const DECL_AND_RETURN(std::forward<L>(l).mesh());
  };

  template<typename T> struct node_t : std::conditional<utility::is_in_ZRC<T>::value, scalar_wrap<T>, typename remove_rvalue_ref<T>::type> {};

  template <typename A, typename B> struct _or_ {typedef void type;};
  template <typename A> struct _or_<A,A>        {typedef A type;};
  template <typename A> struct _or_<void,A>     {typedef A type;};
  template <typename A> struct _or_<A,void>     {typedef A type;};
  template <> struct _or_<void,void>            {typedef void type;};

 }// gfs_expr_tools

 template<typename Tag, typename L, typename R> struct gf_expr : TRIQS_CONCEPT_TAG_NAME(ImmutableGreenFunction){
  typedef typename std::remove_reference<L>::type L_t;
  typedef typename std::remove_reference<R>::type R_t;
  typedef typename gfs_expr_tools::_or_<typename L_t::variable_t,typename R_t::variable_t>::type variable_t;
  typedef typename gfs_expr_tools::_or_<typename L_t::target_t,typename R_t::target_t>::type target_t;
  typedef typename gfs_expr_tools::_or_<typename L_t::option_t,typename R_t::option_t>::type option_t;
  static_assert(!std::is_same<variable_t,void>::value, "Can not combine two gf expressions with different variables");
  static_assert(!std::is_same<target_t,void>::value, "Can not combine two gf expressions with different target");
 
  L l; R r;
  template<typename LL, typename RR> gf_expr(LL && l_, RR && r_):l(std::forward<LL>(l_)), r(std::forward<RR>(r_)) {}
  
  auto mesh() const DECL_AND_RETURN(gfs_expr_tools::combine_mesh()(l,r)); 
  auto singularity() const DECL_AND_RETURN (utility::operation<Tag>()(l.singularity() , r.singularity()));
  
  template<typename KeyType>  auto operator[](KeyType && key)   const DECL_AND_RETURN(utility::operation<Tag>()(l[std::forward<KeyType>(key)] , r[std::forward<KeyType>(key)]));
  template<typename ... Args> auto operator()(Args && ... args) const DECL_AND_RETURN(utility::operation<Tag>()(l(std::forward<Args>(args)...) , r(std::forward<Args>(args)...)));
  friend std::ostream &operator <<(std::ostream &sout, gf_expr const &expr){return sout << "("<<expr.l << " "<<utility::operation<Tag>::name << " "<<expr.r<<")" ; }
 };

 // -------------------------------------------------------------------
 //a special case : the unary operator !
 template<typename L> struct gf_unary_m_expr : TRIQS_CONCEPT_TAG_NAME(ImmutableGreenFunction){
  typedef typename std::remove_reference<L>::type L_t;
  typedef typename L_t::variable_t variable_t;
  typedef typename L_t::target_t target_t;
  typedef typename L_t::option_t option_t;

  L l; 
  template<typename LL> gf_unary_m_expr(LL && l_) : l(std::forward<LL>(l_)) {}
  
  auto mesh() const DECL_AND_RETURN(l.mesh()); 
  auto singularity() const DECL_AND_RETURN(l.singularity());
  
  template<typename KeyType> auto operator[](KeyType&& key) const DECL_AND_RETURN( -l[key]); 
  template<typename ... Args> auto operator()(Args && ... args) const DECL_AND_RETURN( -l(std::forward<Args>(args)...));
  friend std::ostream &operator <<(std::ostream &sout, gf_unary_m_expr const &expr){return sout << '-'<<expr.l; }
 };

 // -------------------------------------------------------------------
 // Now we can define all the C++ operators ...
#define DEFINE_OPERATOR(TAG, OP, TRAIT1, TRAIT2) \
 template<typename A1, typename A2>\
 typename std::enable_if<TRAIT1<A1>::value && TRAIT2 <A2>::value, \
 gf_expr<utility::tags::TAG, typename gfs_expr_tools::node_t<A1>::type, typename gfs_expr_tools::node_t<A2>::type>>::type\
 operator OP (A1 && a1, A2 && a2) { return {std::forward<A1>(a1),std::forward<A2>(a2)};} 

 DEFINE_OPERATOR(plus,       +, ImmutableGreenFunction,ImmutableGreenFunction);
 DEFINE_OPERATOR(minus,      -, ImmutableGreenFunction,ImmutableGreenFunction);
 DEFINE_OPERATOR(multiplies, *, ImmutableGreenFunction,ImmutableGreenFunction);
 DEFINE_OPERATOR(multiplies, *, is_in_ZRC,ImmutableGreenFunction);
 DEFINE_OPERATOR(multiplies, *, ImmutableGreenFunction,is_in_ZRC);
 DEFINE_OPERATOR(divides,    /, ImmutableGreenFunction,ImmutableGreenFunction);
 DEFINE_OPERATOR(divides,    /, is_in_ZRC,ImmutableGreenFunction);
 DEFINE_OPERATOR(divides,    /, ImmutableGreenFunction,is_in_ZRC);
#undef DEFINE_OPERATOR

 // the unary is special
 template<typename A1> 
  typename std::enable_if< 
  ImmutableGreenFunction<A1>::value, 
  gf_unary_m_expr<typename gfs_expr_tools::node_t<A1>::type >
   >::type
   operator - (A1 && a1) { return {std::forward<A1>(a1)};} 

}}//namespace triqs::gf
#endif