#ifndef MARCI_LIST_GRAPH_HH

 #define MARCI_LIST_GRAPH_HH

 #include <iostream>

 namespace marci {

   class list_graph {

     class node_item;

     class edge_item;

   public:

     class node_iterator;

     class each_node_iterator;

     class edge_iterator;

     class each_edge_iterator;

     class out_edge_iterator;

     class in_edge_iterator;

     class sym_edge_iterator;

   private:

     int node_id;

     int edge_id;

     node_item* _first_node;

     node_item* _last_node;

     class node_item {

       friend class list_graph;

       friend class node_iterator;

       friend class each_node_iterator;

       friend class edge_iterator;

       friend class each_edge_iterator;

       friend class out_edge_iterator;

       friend class in_edge_iterator;

       friend class sym_edge_iterator;

       friend std::ostream& operator<<(std::ostream& os, const node_iterator& i);

       friend std::ostream& operator<<(std::ostream& os, const edge_iterator& i);

       list_graph* G;

       int id;

       edge_item* _first_out_edge;

       edge_item* _last_out_edge;

       edge_item* _first_in_edge;

       edge_item* _last_in_edge;

       node_item* _next_node;

       node_item* _prev_node;

     public:

       node_item() { }

     };

     class edge_item {

       friend class list_graph;

       friend class node_iterator;

       friend class each_node_iterator;

       friend class edge_iterator;

       friend class each_edge_iterator;

       friend class out_edge_iterator;

       friend class in_edge_iterator;

       friend class sym_edge_iterator;

       friend std::ostream& operator<<(std::ostream& os, const edge_iterator& i);

       list_graph* G;

       int id;

       node_item* _tail;

       node_item* _head;

       edge_item* _next_out;

       edge_item* _prev_out;

       edge_item* _next_in;

       edge_item* _prev_in;

     public:

       edge_item() { }

     };

     node_item* _add_node() { 

       node_item* p=new node_item;

       p->id=node_id++;

       p->_first_out_edge=0;

       p->_last_out_edge=0;

       p->_first_in_edge=0;

       p->_last_in_edge=0;

       p->_prev_node=_last_node;

       p->_next_node=0;

       if (_last_node) _last_node->_next_node=p;

       _last_node=p;

       if (!_first_node) _first_node=p;

       return p;

     }

     edge_item* _add_edge(node_item* _tail, node_item* _head) {

       edge_item* e=new edge_item;

       e->id=edge_id++;

       e->_tail=_tail;

       e->_head=_head;

       e->_prev_out=_tail->_last_out_edge;

       if (_tail->_last_out_edge) (_tail->_last_out_edge)->_next_out=e;

       _tail->_last_out_edge=e;

       if (!_tail->_first_out_edge) _tail->_first_out_edge=e; 

       e->_prev_in=_head->_last_in_edge;

       if (_head->_last_in_edge) (_head->_last_in_edge)->_next_in=e;

       _head->_last_in_edge=e;

       if (!_head->_first_in_edge) { _head->_first_in_edge=e; } 

       return e;

     }

   public:

     /* default constructor */

     list_graph() : node_id(0), edge_id(0), _first_node(0), _last_node(0) { }

     /* functions to construct iterators from the graph, or from each other */

     each_node_iterator first_node() { return each_node_iterator(_first_node); }

     each_edge_iterator first_edge() { 

       node_item* v=_first_node;

       edge_item* edge=v->_first_out_edge;

       while (v && !edge) { v=v->_next_node; if (v) edge=v->_first_out_edge; }

       return each_edge_iterator(v, edge); 

     }

     out_edge_iterator first_out_edge(const node_iterator& v) { 

       return out_edge_iterator(v); 

     }

     in_edge_iterator first_in_edge(const node_iterator& v) { 

       return in_edge_iterator(v); 

     }

     sym_edge_iterator first_sym_edge(const node_iterator& v) { 

       return sym_edge_iterator(v); 

     }

     node_iterator tail(const edge_iterator& e) { return e.tail_node(); }

     node_iterator head(const edge_iterator& e) { return e.head_node(); }

     node_iterator a_node(const out_edge_iterator& e) { return e.a_node(); }

     node_iterator a_node(const in_edge_iterator& e) { return e.a_node(); }

     node_iterator a_node(const sym_edge_iterator& e) { return e.a_node(); }

     node_iterator b_node(const out_edge_iterator& e) { return e.b_node(); }

     node_iterator b_node(const in_edge_iterator& e) { return e.b_node(); }

     node_iterator b_node(const sym_edge_iterator& e) { return e.b_node(); }

     node_iterator invalid_node() { return node_iterator(); }

     edge_iterator invalid_edge() { return edge_iterator(); }

     out_edge_iterator invalid_out_edge() { return out_edge_iterator(); }

     in_edge_iterator invalid_in_edge() { return in_edge_iterator(); }

     sym_edge_iterator invalid_sym_edge() { return sym_edge_iterator(); }

     /* same methods in other style */

     /* for experimental purpose */

     void get_first(each_node_iterator& v) { v=each_node_iterator(_first_node); }

     void get_first(each_edge_iterator& e) { e=first_edge(); }

     void get_first(out_edge_iterator& e, const node_iterator& v) { 

       e=out_edge_iterator(v); 

     }

     void get_first(in_edge_iterator& e, const node_iterator& v) { 

       e=in_edge_iterator(v); 

     }

     void get_first(sym_edge_iterator& e, const node_iterator& v) { 

       e=sym_edge_iterator(v); 

     }

     void get_tail(node_iterator& n, const edge_iterator& e) { n=tail(e); }

     void get_head(node_iterator& n, const edge_iterator& e) { n=head(e); }

     void get_a_node(node_iterator& n, const out_edge_iterator& e) { n=e.a_node(); }

     void get_a_node(node_iterator& n, const in_edge_iterator& e) { n=e.a_node(); }

     void get_a_node(node_iterator& n, const sym_edge_iterator& e) { n=e.a_node(); }

     void get_b_node(node_iterator& n, const out_edge_iterator& e) { n=e.b_node(); }

     void get_b_node(node_iterator& n, const in_edge_iterator& e) { n=e.b_node(); }

     void get_b_node(node_iterator& n, const sym_edge_iterator& e) { n=e.b_node(); }

     void get_invalid(node_iterator& n) { n=node_iterator(); }

     void get_invalid(edge_iterator& e) { e=edge_iterator(); }

     void get_invalid(out_edge_iterator& e) { e=out_edge_iterator(); }

     void get_invalid(in_edge_iterator& e) { e=in_edge_iterator(); }

     void get_invalid(sym_edge_iterator& e) { e=sym_edge_iterator(); }

     /* for getting id's of graph objects */

     /* these are important for the implementation of property vectors */

     int id(const node_iterator& v) { return v.node->id; }

     int id(const edge_iterator& e) { return e.edge->id; }

     /* adding nodes and edges */

     node_iterator add_node() { return node_iterator(_add_node()); }

     edge_iterator add_edge(const node_iterator& u, const node_iterator& v) {

       return edge_iterator(_add_edge(u.node, v.node)); 

     }

     /* stream operations, for testing purpose */

     friend std::ostream& operator<<(std::ostream& os, const node_iterator& i) { 

       os << i.node->id; return os; 

     }

     friend std::ostream& operator<<(std::ostream& os, const edge_iterator& i) { 

       os << "(" << i.edge->_tail->id << "--" << i.edge->id << "->" << i.edge->_head->id << ")"; 

       return os; 

     }

     class node_iterator {

       friend class list_graph;

       friend class edge_iterator;

       friend class out_edge_iterator;

       friend class in_edge_iterator;

       friend class sym_edge_iterator;

     protected:

       node_item* node;

       friend int list_graph::id(const node_iterator& v); 

     public:

       node_iterator() : node(0) { }

       node_iterator(node_item* _node) : node(_node) { }

       bool is_valid() { return (node!=0); }

       friend bool operator==(const node_iterator& u, const node_iterator& v) { 

 	return v.node==u.node; 

       } 

       friend bool operator!=(const node_iterator& u, const node_iterator& v) { 

 	return v.node!=u.node; 

       } 

       friend std::ostream& operator<<(std::ostream& os, const node_iterator& i);

     };

     class each_node_iterator : public node_iterator {

       friend class list_graph;

     public:

       each_node_iterator() : node_iterator() { }

       each_node_iterator(node_item* v) : node_iterator(v) { }

       each_node_iterator& operator++() { node=node->_next_node; return *this; }

     };

     class edge_iterator {

       friend class list_graph;

       friend class node_iterator;

       friend class each_node_iterator;

     protected:

       edge_item* edge;

       friend int list_graph::id(const edge_iterator& e);

     public:

       edge_iterator() : edge(0) { }

       edge_iterator(edge_item* _edge) : edge(_edge) { }

       bool is_valid() { return (edge!=0); }

       friend bool operator==(const edge_iterator& u, const edge_iterator& v) { 

 	return v.edge==u.edge; 

       } 

       friend bool operator!=(const edge_iterator& u, const edge_iterator& v) { 

 	return v.edge!=u.edge; 

       } 

     protected:

       node_iterator tail_node() const { return node_iterator(edge->_tail); }

       node_iterator head_node() const { return node_iterator(edge->_head); }

     public:

       friend std::ostream& operator<<(std::ostream& os, const edge_iterator& i);

     };

     class each_edge_iterator : public edge_iterator {

       friend class list_graph;

       node_item* v;

     public:

       each_edge_iterator() : edge_iterator(), v(0) { }

       each_edge_iterator(node_item* _v, edge_item* _e) : edge_iterator(_e), v(_v) { }

       each_edge_iterator& operator++() { 

 	edge=edge->_next_out; 

 	while (v && !edge) { v=v->_next_node; if (v) edge=v->_first_out_edge; }

 	return *this;

       }

     };

     class out_edge_iterator : public edge_iterator {

       friend class list_graph;

       node_item* v;

     public:

       out_edge_iterator() : edge_iterator(), v(0) { }

     protected:

       out_edge_iterator(const node_iterator& _v) : v(_v.node) { edge=v->_first_out_edge; }

     public:

       out_edge_iterator& operator++() { edge=edge->_next_out; return *this; }

     protected:

       node_iterator a_node() const { return node_iterator(v); }

       node_iterator b_node() const { 

 	return (edge->_tail==v) ? node_iterator(edge->_head) : node_iterator(v); }

     };

     class in_edge_iterator : public edge_iterator {

       friend class list_graph;

       node_item* v;

     public:

       in_edge_iterator() : edge_iterator(), v(0) { }

     protected:

       in_edge_iterator(const node_iterator& _v) : v(_v.node) { 

 	edge=v->_first_in_edge; 

       }

     public:

       in_edge_iterator& operator++() { edge=edge->_next_in; return *this; }

     protected:

       node_iterator a_node() const { return node_iterator(v); }

       node_iterator b_node() const { 

 	return (edge->_tail==v) ? node_iterator(edge->_head) : node_iterator(v); }

     };

     class sym_edge_iterator : public edge_iterator {

       friend class list_graph;

       bool out_or_in; //1 iff out, 0 iff in

       node_item* v;

     public:

       sym_edge_iterator() : edge_iterator(), v(0) { }

     protected:

       sym_edge_iterator(const node_iterator& _v) : v(_v.node) { 

 	out_or_in=1;

 	edge=v->_first_out_edge; 

 	if (!edge) { edge=v->_first_in_edge; out_or_in=0; }

       }

     public:

       sym_edge_iterator& operator++() { 

 	if (out_or_in) { 

 	  edge=edge->_next_out; 

 	  if (!edge) { out_or_in=0; edge=v->_first_in_edge; }

 	} else {

 	  edge=edge->_next_in; 

 	}

 	return *this;

       }

     protected:

       node_iterator a_node() const { return node_iterator(v); }

       node_iterator b_node() const { 

 	return (edge->_tail==v) ? node_iterator(edge->_head) : node_iterator(v); }

     };

   };

 } //namespace marci

 #endif //MARCI_LIST_GRAPH_HH