This function can be used before saving a file to make sure it has a filename that is sanitized and unique for the given directory.
If the filename is not unique, then a number will be added to the filename before the extension, and will continue adding numbers until the filename is unique.
The callback is passed three parameters:
Note: In the WordPress code comments the third parameter is described as being the file extension. Looking at the function itself, this is not true. The callback allows the caller to use their own method to create unique file names. If defined, the callback should take three arguments - directory, base filename, and extension and provide a unique filename.
$newfilename = wp_unique_filename( $path_being_saved_to, $filename_to_check );
wp_unique_filename() is located in