Access log

[gemione]

I am trying write the day the person logs in in a txt file.
Format: 1 2 3 4 6 8 9
delimieter is a space.
I dont want duplicate entries but my code will continue to add a day even if it already exists.
My Code:

<? 
	//**Catch variable values from Flash program**//
	$filename = $_POST['filename'];
	//server date(d) from flash (didnt know how to in PHP at the time)
	$day = $_POST['day'];
	//**Open/Create current user access log and copy contents to string**//
	$file = fopen($_SERVER['DOCUMENT_ROOT'] . "/logs/$filename", "a+"); 
	$currentLogStr = fread($file, filesize($filename));
	fclose($file);
	//**Check to see if log has entries**//
	if ($currentLogStr != ""){
		//**If log has entries make array out of data**//
		$currentLog = explode(" ",$currentLogStr);
		//**Check to see if current day is later than last entry date in $currentLog**//
		if ($day > $currentLog[count($currentLog-1)]) //Can I use end($currentLog) here?
		{	
			//**If current day later, add to log**//
			$file = fopen($_SERVER['DOCUMENT_ROOT'] . "/logs/$filename", "a+"); 
			fwrite($file,$day . " ");
			fclose($file);	
		}
		//**If current day not later than last entry do nothing**//
	}else
	{	
		//**If log has no entries add one**//
		$file = fopen($_SERVER['DOCUMENT_ROOT'] . "/logs/$filename", "a+"); 
		fwrite($file,$day . " ");
		fclose($file);	
	}
?> 

Please help. Ocnce it stops repeating I am done my project (this one anyway)

Thanks,

Pete