If i may

The file extension can easily be 'tricked'; i gladly took your class into use but adjusted the $this->icons keys to resemble mime-types instead.

Then there are two variants available, one for windows host another for unix:

function get_file_type() {
if(function_exists('shell_exec') === TRUE) {
$dump = shell_exec(sprintf('file -bi %s', $this -> filename));
$info = explode(';', $dump); // split has deprecated
return $info[0];
} else {
$fo = finfo_open(FILEINFO_MIME);
$info = finfo_file($fo, $this -> filename);
finfo_close($fo);
return $info;
}
return FALSE;
}