Randomize uploaded file names

/**
 * Completely randomize the filename of the upload.
 * 
 * Change the variable $hash_len based on the random
 * string length desired. Example creates a random
 * string 36 characters long.
 */
add_filter( 'sanitize_file_name', function( $filename ) {
    
    // How long a random string do we want?
    $hash_len = 36;
    
    // Get the file extension.
    $ext = pathinfo( $filename, PATHINFO_EXTENSION );
    
    if ( preg_match( '/^[a-f0-9]{'. $hash_len . '}-.*/', $filename ) ) {
        $filename = substr( $filename, $hash_len + 1 );
    }

    $key = sha1( random_bytes(32) );
    $key = substr( $key, 0, $hash_len );

    return "$key.$ext";
}, 10 );