using System;
using System.Collections.Generic;
 
namespace DoFactory.GangOfFour.Interpreter.RealWorld
{
	/// 

	/// MainApp startup class for Real-World 
	/// Interpreter Design Pattern.
	/// 
  class MainApp

  {
	/// 

	/// Entry point into console application.
	/// 
    static void Main()
    {
      string roman = "MCMXXVIII";
      Context context = new Context(roman);
 
      // Build the 'parse tree'
      List tree = new List();
      tree.Add(new ThousandExpression());
      tree.Add(new HundredExpression());
      tree.Add(new TenExpression());
      tree.Add(new OneExpression());
 
      // Interpret
      foreach (Expression exp in tree)
      {
        exp.Interpret(context);
      }
 
      Console.WriteLine("{0} = {1}", roman, context.Output);
 
      // Wait for user
      Console.ReadKey();
    }
  }
 
	/// 

	/// The 'Context' class
	/// 
  class Context
  {
    private string _input;
    private int _output;
 
    // Constructor
    public Context(string input)
    {
      this._input = input;
    }
 
    // Gets or sets input
    public string Input
    {
      get { return _input; }
      set { _input = value; }
    }
 
    // Gets or sets output
    public int Output
    {
      get { return _output; }
      set { _output = value; }
    }
  }
 
	/// 

	/// The 'AbstractExpression' class
	/// 
  abstract class Expression
  {
    public void Interpret(Context context)
    {
      if (context.Input.Length == 0)
        return;
 
      if (context.Input.StartsWith(Nine()))
      {
        context.Output += (9 * Multiplier());
        context.Input = context.Input.Substring(2);
      }
      else if (context.Input.StartsWith(Four()))
      {
        context.Output += (4 * Multiplier());
        context.Input = context.Input.Substring(2);
      }
      else if (context.Input.StartsWith(Five()))
      {
        context.Output += (5 * Multiplier());
        context.Input = context.Input.Substring(1);
      }
 
      while (context.Input.StartsWith(One()))
      {
        context.Output += (1 * Multiplier());
        context.Input = context.Input.Substring(1);
      }
    }
 
    public abstract string One();
    public abstract string Four();
    public abstract string Five();
    public abstract string Nine();
    public abstract int Multiplier();
  }
 
	/// 

	/// A 'TerminalExpression' class
	/// 
	/// Thousand checks for the Roman Numeral M 
	/// 
	/// 

  class ThousandExpression : Expression
  {
    public override string One() { return "M"; }
    public override string Four() { return " "; }
    public override string Five() { return " "; }
    public override string Nine() { return " "; }
    public override int Multiplier() { return 1000; }
  }
 
	/// 

	/// A 'TerminalExpression' class
	/// 
	/// Hundred checks C, CD, D or CM
	/// 
	/// 

  class HundredExpression : Expression
  {
    public override string One() { return "C"; }
    public override string Four() { return "CD"; }
    public override string Five() { return "D"; }
    public override string Nine() { return "CM"; }
    public override int Multiplier() { return 100; }
  }
 
	/// 

	/// A 'TerminalExpression' class
	/// 
	/// Ten checks for X, XL, L and XC
	/// 
	/// 
  class TenExpression : Expression
  {
    public override string One() { return "X"; }
    public override string Four() { return "XL"; }
    public override string Five() { return "L"; }
    public override string Nine() { return "XC"; }
    public override int Multiplier() { return 10; }
  }
 
	/// 

	/// A 'TerminalExpression' class
	/// 
	/// One checks for I, II, III, IV, V, VI, VI, VII, VIII, IX
	/// 
	/// 
  class OneExpression : Expression
  {
    public override string One() { return "I"; }
    public override string Four() { return "IV"; }
    public override string Five() { return "V"; }
    public override string Nine() { return "IX"; }
    public override int Multiplier() { return 1; }
  }
}