Tom's answer to april 1st dev hour

Martian Rovers.linq

<Query Kind="Program" />

void Main()
{
	var input = @"5 5
	1 2 N
	LMLMLMLMM
	3 3 E
	MMRMMRMRRM";

	var north = new Heading("N", p => p.Y++);
	var east = new Heading("E", p => p.X++);
	var south = new Heading("S", p => p.Y--);
	var west = new Heading("W", p => p.X--);
	west.Right = east.Left = north;
	north.Right = south.Left = east;
	east.Right = west.Left = south;
	south.Right = north.Left = west;
	
	var headings = new[] { north, east, south, west };
		
	var lines = input.Split(new[] {'\r', '\n' }, StringSplitOptions.RemoveEmptyEntries);
	var dimensions = lines[0]
				.Split(' ')
				.Select(s => int.Parse(s.Trim()))
				.ToArray();
	var top = dimensions[0];
	var left = dimensions[1];
	
	for (int i = 1; i < lines.Length; i += 2)
	{
		var positionText = lines[i];
		var position = RoverPosition.Parse(positionText);
		var instructionText = lines[i+1];
		foreach(var instruction in instructionText)
		{
			var currentHeading = headings.Single(s => s.Name == position.Heading);
			switch(instruction)
			{
				case 'L':
					position.Heading = currentHeading.Left.Name;
					break;
				case 'R':
					position.Heading = currentHeading.Right.Name;
					break;
				case 'M':
					currentHeading.Forward(position);
					if (position.X < 0) position.X = 0;
					if (position.X > left) position.X = left;
					if (position.Y < 0) position.Y = 0;
					if (position.Y > top) position.Y = top;
					break;
			}
		}
		
		position.ToString().Dump();
	}
}

class Heading
{
	public string Name { get; }
	
	public Heading Left { get; set; }
	
	public Heading Right { get; set; }
	
	public Action<RoverPosition> Forward { get; }
	
	public Heading(string name, Action<RoverPosition> forwardAction)
	{
		Name = name;
		Forward = forwardAction;
	}
}

class RoverPosition
{
	public int X { get; set; }
	public int Y { get; set; }
	public string Heading { get; set; }
	
	public static RoverPosition Parse(string input)
	{
		var parts = input.Split(' ');
		var position = new RoverPosition
		{
			X = int.Parse(parts[0]),
			Y = int.Parse(parts[1]),
			Heading = parts[2]
		};
		return position;
	}

	public override string ToString() => $"{X} {Y} {Heading}";
}