<?php

class hilbert_square {
	public static $Directions = array(
		'west' => array( 'north', 'east', 'west', 'south', 'west', 'west', 'south' ),
		'east' => array( 'south', 'west', 'east', 'north', 'east', 'east', 'north' ),
		'north' => array( 'west', 'south', 'north', 'east', 'north', 'north', 'east' ),
		'south' => array( 'east', 'north', 'south', 'west', 'south', 'south', 'west' )
	);

	public $scale;
	public $level;
	public $callback;

	private $x;
	private $y;

	public function __construct($length, $callback){
		$this->level = sqrt(intval($length));
		$this->scale = 1;
		$this->callback = $callback;
		$this->x = 0;
		$this->y = 0;

		if(!is_callable($this->callback)) exit('hilbert_cube: callback argument is not a function');
	}

	private function walk($direction){
		switch($direction){
			case 'north':
				$this->y -= $this->scale;
				break;
			case 'south':
				$this->y += $this->scale;
				break;
			case 'east':
				$this->x += $this->scale;
				break;
			case 'west':
				$this->x -= $this->scale;
				break;
		}
		//echo "\n$direction - ", $this->x, ',', $this->y;
		call_user_func($this->callback, $this->x, $this->y);
	}

	private function hilbert($level, $direction='north'){
		$dirs = self::$Directions[$direction];
		for($i=0;$i<6;$i+=2){
			if($level != 1){
				$hbResult = $this->hilbert($level-1,$dirs[$i]);
				if($hbResult){
					return $hbResult;
				}
			}
			$moveResult = $this->walk($dirs[$i+1]);
			if($moveResult){
				// A non-false return from either function means
				// we've found our target, so we can break out
				// of the recursion.
				return $moveResult;
			}
		}
		if($level != 1) {
			$hbResult = $this->hilbert($level-1, $dirs[6]);
			if($hbResult){
				return $hbResult;
			}
		}
		return false;
	}

	public function run(){
		call_user_func($this->callback, $this->x, $this->y);
		$this->hilbert($this->level);
	}

}
?>