<?php

class ELO {
	
	function Rank(&$player1, &$player2, $winner = 1) {
		$expected_player1 = $player1;
		$expected_player2 = $player2;
		
		ELO::expected($expected_player1, $expected_player2);
		
		$K = ELO::getK($player1, $player2);
		
		$score1 = 0;
		$score2 = 0;
		
		switch($winner) {
			case 1:
				$score1 = 1;
				$score2 = 0;
				break;
			case 2:
				$score1 = 0;
				$score2 = 1;
				break;
			case 0:
				$score1 = .5;
				$score2 = .5;
				break;
		}
		
		$player1_new = $player1 + $K * ($score1 - $expected_player1);
		$player2_new = $player2 + $K * ($score2 - $expected_player2);
		
		$player1 = $player1_new;
		$player2 = $player2_new;
	}
	
	function expected(&$player1, &$player2) {
		
		$p1 = 1 / (1 + pow(10,(($player2 - $player1) / 400)));
		$p2 = 1 / (1 + pow(10,(($player1 - $player2) / 400)));
		
		$player1 = $p1;
		$player2 = $p2;
	}
	
	function getK($player1, $player2) {
		return ($player1 + $player2 > 4200 ? 16 : 32);
	}
	
}

?>