PHP Class to create logfile logging actions with messages

Logger.php

/*
* NOTES: 
*
* TODO: Consider some static methods or running the logger as a plugin
*
*
*/

class Logger {

    public $dir;
    public $file;
    protected $handle;
    public $logged;
    public $file_list = array();
    static $count = 0;

    /**
     * Create logfile with log messages
     * 
     * requires the directory where log files will be created 
     * and another parameter for a filename
     * 
     * 
     * @param string $dir with trailing /
     * @param string $filename without any extensions
     * 
     * Best practise: pass filename param equal to category of what is logged client/action/type 
     */
    public function __construct($dir, $filename)
    {
        $this->date = date('y-m-d H:i:s');
        $this->dir = $dir;
        if ($filename)
            $this->file = $this->fileName($filename);
        $this->fileList();
    }

    /**
     * Write a msg to a file, 
     * 
     * Using the FILE_APPEND flag to append the content to the end of the file 
     *  
     * and LOCK_EX flag to prevent anyone else writing to the file at the same time
     * 
     * @param type $msg
     * 
     * Date and EOL is prepended and appended to msg
     *  
     * @return boolean
     */
    function logAction($msg)
    {
        static::$count++;
        $sp = ': ';
        $this->logged = file_put_contents($this->dir . $this->file, $this->date . $sp . self::$count . $sp . $msg . PHP_EOL, FILE_APPEND | LOCK_EX);
        return $this->logged;
    }

    function fileName($filename)
    {
        $date = date('Y-m');
        $file_name = $filename . '_' . $date . '.log';

        return $file_name;
    }

    function fileList()
    {
        $this->handle = opendir($this->dir);
        if ($this->handle) {

            /* This is the correct way to loop over the directory. */
            while (false !== ($entry = readdir($this->handle))) {
                $this->file_list[] = $entry;
            }
            closedir($this->handle);
        }        
        return $this->file_list;
    }
    
    function printFileList(){
        $str = '';
        foreach ($this->file_list as $file => $name) {
            $str .= "File #{$file} : " . htmlspecialchars($name) . "<br />\n";
        }
        return $str;
    }

    function findFile($filename)
    {
        if (in_array($filename, $this->file_list))
            return true;
    }

    function readFile()
    {
        $lines = file($this->dir.$this->file);
        $str = '';
        // Loop through our array, show HTML source as HTML source; and line numbers too.
        foreach ($lines as $line_num => $line) {
            $str .= "#<b>{$line_num}</b> : " . htmlspecialchars($line) . "<br />\n";
        }
        return $str;
    }

}