using System;
using M17N.Core;

namespace M17N.Core
{
  public class MPlist
  {
    private MSymbol key;
    private object val;
    private MPlist next;

    public MPlist ()
    {
      key = null;
      val = null;
      next = null;
    }

    public bool tailp { get { return (object) key == null; } }

    public new string ToString ()
    {
      string str = "";

      for (MPlist p = this; ! p.tailp; p = p.next)
	{
	  str += (p == this ? "(" : " ") + p.key.ToString () + ":";
	  if (p.val is MSymbol)
	    str += ((MSymbol) p.val).ToString ();
	  else if (p.val is MPlist)
	    str += ((MPlist) p.val).ToString ();
	}
      return str + ")";
    }

    public object get (MSymbol key)
    {
      if ((object) key == null)
	return null;
      for (MPlist p = this; ! p.tailp; p = p.next)
	if (p.key == key)
	  return p.val;
      return null;
    }

    public object put (MSymbol key, object val)
    {
      MPlist p;

      for (p = this; ! p.tailp; p = p.next)
	if (p.key == key)
	  {
	    if (val != null)
	      p.val = val;
	    else
	      p.pop ();
	    return val;
	  }
      if (val != null)
	{
	  p.key = key;
	  p.val = val;
	  p.next = new MPlist ();
	}
      return val;
    }

    public object push (MSymbol key, object val)
    {
      MPlist p = new MPlist ();

      p.key = this.key;
      p.val = this.val;
      p.next = this.next;
      this.key = key;
      this.val = val;
      this.next = p;

      return val;
    }

    public object pop ()
    {
      if (tailp)
	return null;

      object val = this.val;

      this.key = this.next.key;
      this.val = this.next.val;
      this.next = this.next.next;
      return val;
    }

    public object add (MSymbol key, object val)
    {
      MPlist p;

      for (p = this; ! p.tailp; p = p.next);
      if (val != null)
	{
	  p.key = key;
	  p.val = val;
	  p.next = new MPlist ();
	}
      return val;
    }
  }
}