//Define the Element Interface and Handler Objects.

//Define the ElementBase abstract class to be used as the base class for all classes that can be visited.
//This abstract class defines the Accept() method, which accepts the visitor object as a parameter.
public abstract class ElementBase
{
public abstract void Accept(IVisitor visitor);
}

//The Element class (object) defines the base class for a type of class that can be visited and invokes the Visit() method on the visitor class (object).
public class Element : ElementBase
{
public int Weight { get; set; }
public Element Next { get; set; }
public Element Child { get; set; }

public override void Accept(IVisitor visitor)
{
visitor.Visit(this);
}

private int GetNumber(Context context)
{
int atSpace = context.Input.IndexOf(' ');
int number = int.Parse(context.Input.Substring(1, atSpace));
context.Input = context.Input.Substring(atSpace + 1);
return number;
}

public void Parse(Context context)
{
string starters = "LTME";
if (context.Input.Length > 0 && starters.IndexOf(context.Input[0]) >= 0)
{
switch (context.Input[0])
{
case 'L':
Next = new Lab();
break;
case 'T':
Next = new Test();
break;
case 'M':
Next = new MidTerm();
break;
case 'E':
Next = new Exam();
break;
}

Next.Weight = GetNumber(context);
if (context.Input.Length > 0 && context.Input[0] == '(')
{
context.Input = context.Input.Substring(1);
Next.Child = new Element();
Next.Child.Parse(context);
Element e = Next.Child;
while (e != null)
{
e.Weight = e.Weight * Next.Weight / 100;
e = e.Next;
}

context.Input = context.Input.Substring(2);
}

Next.Parse(context);
}
}
}

//The Course class (object) inherits from the Element base class and defines one type of class that can be visited.
//The Course class invokes the Visit() method on the visitor class (object).
public class Course : Element
{
public string Name { get; set; }

public Course(Context context)
{
Name = context.Input.Substring(0, 6);
context.Input = context.Input.Substring(7);
}

public override void Accept(IVisitor visitor)
{
visitor.Visit(this);
}
}

//The Lab class (object) inherits from the Element base class and defines another type of class that can be visited.
//The Lab class invokes the Visit() method on the visitor class (object).
public class Lab : Element
{
public override void Accept(IVisitor visitor)
{
visitor.Visit(this);
}
}

//The Test class (object) inherits from the Element base class and defines another type of class that can be visited.
//The Test class invokes the Visit() method on the visitor class (object).
public class Test : Element
{
public override void Accept(IVisitor visitor)
{
visitor.Visit(this);
}
}

//The MidTerm class (object) inherits from the Element base class and defines another type of class that can be visited.
//The MidTerm class invokes the Visit() method on the visitor class (object).
public class MidTerm : Element
{
public override void Accept(IVisitor visitor)
{
visitor.Visit(this);
}
}

//The Exam class (object) inherits from the Element base class and defines another type of class that can be visited.
//The Exam class invokes the Visit() method on the visitor class (object).
public class Exam : Element
{
public override void Accept(IVisitor visitor)
{
visitor.Visit(this);
}
}