/* updated with xml parsing functions */

using System;
using System.IO;
using System.Text;
using System.Xml;

public interface student
{
   object accept(studentvisitor v);
}

public interface studentvisitor
{
   object visit(grad s);
   object visit(undergrad s);
   object visit(nilstudent s);
}

public interface stufriend
{ }

public class studentbase : student
{
  public readonly string name;
  protected int tuition;
  protected double gpa;
  public int gettuition(stufriend sf) { return tuition; }
  public void settuition(stufriend sf,int g)
     { tuition = g; }
  public double getgpa(stufriend sf) { return gpa; }
  public studentbase(string n, double g)
    { name = n;  gpa = g; }
  public virtual object accept(studentvisitor s) 
     {return null;}
  public student next;
}

public class grad : studentbase, student
{
  public readonly string thesis;
  public grad(string n, double g, string t) : base(n,g)
    { thesis = t;  tuition = 2000; }
  public override object accept(studentvisitor s) 
    { return s.visit(this); }
}

public class undergrad : studentbase, student
{
  public readonly string major;
  public undergrad(string n, double g, string t) : base(n,g)
    { major = t;  tuition = 1500; }
  public override object accept(studentvisitor s) 
    { return s.visit(this); }
}

public class nilstudent : student
{
  public object accept(studentvisitor s) { return s.visit(this); }
}

////// visitor classes

public class printinfo : studentvisitor, stufriend
{
  public object visit(grad g)
   {
      Console.WriteLine(g.name + " is a grad student, ");
      Console.WriteLine("tuition is " + g.gettuition(this));
      return g.next.accept(this);
   } 
  
  public object visit(undergrad u)
   {
      Console.WriteLine(u.name + " is an undergrad, ");
      Console.WriteLine("tuition is " + u.gettuition(this));
      return u.next.accept(this);
   } 
  public object visit(nilstudent n)
   {
      return null;
   } 
} // printinfo


public class tuitionadjuster : studentvisitor, stufriend
{  
   private int uamt, gamt;  private int sum = 0;
   public tuitionadjuster(int u, int g)
     { uamt = u;  gamt = g; }

   public object visit(undergrad u)
     { u.settuition(this, uamt+u.gettuition(this));
       sum += u.gettuition(this);
       return u.next.accept(this);
     }
   public object visit(grad g)
     { g.settuition(this, gamt+g.gettuition(this));
       sum += g.gettuition(this);
       return g.next.accept(this);
     }
   public object visit(nilstudent n)
     {
       return sum;
     }
}

public class students
{
  public static void Main()
  {  
    grad g1 = new grad("adam",2.02,"networks");
    undergrad u1 = new undergrad("ted",3.0,"cs");
    undergrad u2 = new undergrad("mary",4.0,"math");
    
    u1.next = g1;  g1.next = u2;  
    u2.next = new nilstudent();
    
    student l = u1;
    printinfo printer = new printinfo();
    l.accept(printer);
    int sum = (int)l.accept(new tuitionadjuster(200,300));
    l.accept(new printinfo());
    Console.WriteLine("total tuition: "+sum);
    student l2 = parse("stu.xml");
    Console.WriteLine("from xml file: ----- ");
    l2.accept(printer);
  } // main

////////////// xml parser

public static student cons(studentbase a, student b)
 { a.next = b; return a; }

public static student parse(string filename)
{
  student sl = new nilstudent();  // list to be built
  XmlTextReader reader = new XmlTextReader(filename);
try {
  // look for the students root node:
  while (reader.NodeType != XmlNodeType.Element ||
         reader.Name != "students")
     { reader.Read(); }
  reader.Read(); 
  while (!(reader.NodeType==XmlNodeType.EndElement &&
           reader.Name == "students"))
   {
     if (reader.Name=="undergrad") 
      sl = parseu(sl,reader);
     else if (reader.Name=="grad")
      sl = parseg(sl,reader);
     reader.Read();     
   }  // while
} catch (Exception ee) {Console.WriteLine(ee);}
  return sl;
} // parse

public static student parseu(student sl,XmlTextReader reader)
{ 
   undergrad newu;
   string name="", major="";
   double gpa;
   reader.MoveToAttribute(reader.AttributeCount-1);
   if (reader.Name == "name") name = reader.Value; 
   reader.MoveToContent();
   while (reader.Name !="gpa") reader.Read();
   gpa = double.Parse(reader.ReadElementString());
   while (reader.Name !="major") reader.Read();
   major = reader.ReadElementString();
   newu = new undergrad(name,gpa,major);
   newu.next = sl;
   while (reader.NodeType!=XmlNodeType.EndElement || 
          reader.Name!="undergrad") 
       reader.Read();
   return newu;
}

public static student parseg(student sl,XmlTextReader reader)
{ 
   grad newg;
   string name="", thesis="";
   double gpa;
   reader.MoveToAttribute(0);
   if (reader.Name == "name") name = reader.Value; 
   reader.MoveToContent();
   while (reader.Name !="gpa") reader.Read();
   reader.MoveToContent();
   gpa = double.Parse(reader.ReadElementString());
   while (reader.Name !="thesis") reader.Read();
   thesis = reader.ReadElementString();
   newg = new grad(name,gpa,thesis);
   newg.next = sl;
   while (reader.NodeType!=XmlNodeType.EndElement || 
          reader.Name!="grad") 
       reader.Read();
   return newg;
}

}// public class students