class Object{//由于不知道snake的节点里面存放什么，先设计成抽象基类
 public:
  Object(){}//constructor
  virtual bool isEqual(Object &) = 0;
  virtual bool operator==(Object &) = 0;
  virtual void show() = 0;
  virtual ~Object(){};
}

class Node{//节点
 private:
  Object *info;
  Node *prev, *next;
 public:
  Node(){prev = next = info = 0;}
  Node& operator=(Node &);

  void getInfo();
  void setInfo();
  friend class Snake;
}
class Snake{//实际是实现一个双向链表，并且可以分别在头尾插入节点
 private:
  //int posX, posY;
  Node *head, *tail;
 public:
  Snake(){head = tail = 0;}
  ~Snake();

  void addNode(Node *);//在尾部加入节点
  void addNodeFirst(Node *);//在头部加入节点
  Node* deleteNode(Node *);//not physically delete
  Node* lookUpNode(Object &);//查找某一节点
  void deleteSnake();//physically delete
  void drawSnake();//这个函数以后和OpenGl库结合
  //for debug
  void printSnake();
}

void Snake::addNode(Node *node){
 if(head==NULL)
 {
  head = tail = node;
  node->prev = NULL;
  node->next = NULL;  
 }  
 else
 {
  tail->next = node;
  node->prev = tail;
  tail = node;
  node->next = NULL;
 }
  
}

void Snake::addNodeFirst(Node *node){
 if(head==NULL)
 {
  head=tail=node;
  node->prev = node->next = NULL;
 }
 else
 {
  node->next = head;
  head->prev = node;
  head = node;
  node->prev = NULL;
 }
}

Node* snake::deleteNode(Node *node){
 if(node==head)
 {
  if(node==tail)
  {
   head = tail = NULL;
   //node = NULL;//delete
  }
  else
  {
   head = head->next;
   head->prev = NULL;
   node->next = NULL;
   //node = NULL;//delete
  }
 }
 else
 {
  node->prev->next = node->next;
  if(node==tail)
   tail = node->prev;
  else
   node->next->prev = node->prev;
  node->prve = NULL;
  node->next = NULL;
  //node = NULL;//delete
 }

 return node;
}

Node* Snake::lookUpNode(Object &obj){
 Node* p = head;
 
 while(p)
 {
  if(*(p->info)==obj)
   return p;
  else
   p = p->next;
 }

 return NULL;
}

void Snake::deleteSnake(){
 Node *p, *q;
 p =  head;

 while(p)
 {
  delete p->info;
  q = p;
  p = p->next;
  delete q;
 }
}

void Snake::printSnake(){
 Node* p = head;

 while(p)
 {
  p->info->show();
  p = p->next;
 }
}