{ pkgs, lib, ... }:
''
  # rsync -rlptzv --progress --delete --exclude=.git --exclude=.vscode --exclude=result --exclude=channels/ /Users/os/src/fc.qemu os@hydra01:
  # rsync -rlptzv --progress --rsh="ssh -J fcio-whq-jump" --delete --exclude=.git --exclude=.vscode --exclude=result --exclude=channels/ /Users/os/src/fc-nixos/ os@patty:fc-nixos/


  DEFAULT_JUMPHOST="fcio-whq-jump"

  _parse_rsync_args() {
  	# reset pre-defined variables that are read and manipulated throughout this function
  	unset JUMPHOST
  	# arrays are bash or zsh specific
  	RSYNC_OPTS=("-rlptzv" "--progress" "--delete" "--exclude=.git" "--exclude=.vscode" "--exclude=result" "--exclude=channels/" "--exclude=.mypy_cache")

  	while getopts ':Jj:' OPT; do
  		case $OPT in 
  			j)
  				if [ -n "$JUMPHOST" ]; then
  					echo "-j and -J are conflicting arguments" >&2
  					return 1
  				fi
  				JUMPHOST="$OPTARG"
  				;;
  			J)
  				if [ -n "$JUMPHOST" ]; then
  					echo "-j and -J are conflicting arguments" >&2
  					return 1
  				fi
  				JUMPHOST="$DEFAULT_JUMPHOST"
  				;;
  			?)
  				echo "rsyncrepo [-J] [-j <jumphost>] <directory> <hostname> [target dir name]"
  				return 1
  				;;
  		esac
  	done

  	# trim CLI parameters
  	shift "$(($OPTIND -1))"

  	RR_FROM="$1"
  	RR_TO="$2"
    RR_TARGET="$3"
  }

  _do_rsync() {
  	# parameter check
  	if [ -z "$1" ] || [ -z "$2" ]; then
  		echo "Missing arguments, required: <directory> <hostname>" >&2
  		return 1
  	fi

  	if [ -n "$JUMPHOST" ]; then
  		RSYNC_OPTS+=("--rsh=${lib.getExe pkgs.openssh} -J ''${JUMPHOST}")
  	fi

  	for OPTI in "''${RSYNC_OPTS[@]}"; do
  		echo "$OPTI"
  	done

  	# If no $3 is specified, we sync /path/to/dir/ to hostname:dir
    if [ -z "$3" ]; then
      RR_DEST="''${2}:$(basename $(realpath "''${1}"))"
    else
      RR_DEST="''${2}:''${3}"
    fi

  	echo "Syncing ''${1} to ''${RR_DEST}…"

  	# ensure trailing slash for src to avoid recreating directory
  	${lib.getExe pkgs.rsync} "''${RSYNC_OPTS[@]}"  "''${1}/" "''${RR_DEST}"
  }

  rsyncrepo() {
  	_parse_rsync_args "$@"
  	# inherits parsed arguments through variables
  	_do_rsync "$RR_FROM" "$RR_TO" "$RR_TARGET"
  }

  rsynchydra() {
  	_parse_rsync_args "$@"
  	_do_rsync "$RR_FROM" "hydra01" "$RR_TARGET"
  }
''