using System;
using System.Runtime.Serialization;
using System.Collections.Generic;

namespace WorldOfPeacecraft
{
	class Pathwalker
	{
		private LinkedList<Coordinate> Coords;

		public void Stop()
		{
			Coords = null;
		}

		public bool HasMoreSteps()
		{
			return Coords != null && Coords.Count >= 2;
		}

		public string NextStep ()
		{
			if (Coords == null) {
				throw new PathwalkerException ("There are no coordinates set");
			}
			if (Coords.Count < 2) {
				throw new PathwalkerException ("There are no more steps to take");
			}
			Coordinate src = Coords.First.Value;
			Coords.RemoveFirst ();
			Coordinate dst = Coords.First.Value;
			int distance = Math.Abs (src.X - dst.X) + Math.Abs (src.Y - dst.Y);
			if (distance > 1) {
				throw new PathwalkerException ("The distance between (" + src.X + "|" + src.Y + ") and (" + dst.X + "|" + dst.Y + ") is greater than 1");
			}
			string command;
			if (src.X > dst.X) {
				command = "mv:lft";
			} else if (src.X < dst.X) {
				command = "mv:rgt";
			} else if (src.Y > dst.Y) {
				command = "mv:up";
			} else if (src.Y < dst.Y) {
				command = "mv:dwn";
			} else {
				command = NextStep ();
			}
			return command;
		}

		public void SetCoords(LinkedList<Coordinate> coords)
		{
			this.Coords = coords;
		}
	}

	public class PathwalkerException : Exception
	{
		public PathwalkerException () : base()
		{
		}

		public PathwalkerException (string message) : base(message)
		{
		}

		public PathwalkerException (SerializationInfo info, StreamingContext context) : base(info, context)
		{
		}

		public PathwalkerException (string message, Exception innerException) : base(message, innerException)
		{
		}
	}
}