linkalisation

#!/bin/bash

#set -e

show_usage() {
	cat <<- USAGE >&2
		Creates symbolic links to files in the source directory from the target directory, recursively,
		but only if a file exists in the target directory with the same name.
		Before a link is created, the existing namesake file in the target is suffixed with '.upstream'
		Both directores must have the same structure. I.e source and target files must have the same path
		relative to source and target, as roots.
		Usage:
			$(basename $0) [-f] -s SOURCE -t TARGET | -r TARGET

		Where:
			-f	Force replacement of existing symlinks.
			-r	Remove links and restore .upstream files to their original names.
USAGE
	exit 85
}

if [ -z $# ]; then
	show_usage
fi

check_path() {
	typeset -n root=$1
	root=$(readlink -e "$2")/
	if [ $? -ne 0 ]; then
		echo "Directory ./$2 doesn't exist. Exiting."
		exit 1
	fi
}

while [ $# -gt 0 ]; do
case "$1" in
	-s|--source)
		check_path sRoot $2
		shift
	;;
	-t|--target)
		check_path tRoot $2
		shift
	;;
	-r|--restore)
		check_path rRoot $2
		shift
	;;
	-f|--force)
		FORCE_LINKS=true
	;;
	-h|--help)
		show_usage
	;;
	*)
		show_usage
  esac
  shift
done

if [ -z "$sRoot" -a -z "$tRoot" -a ! -z "$rRoot" ]; then
	echo -e "Restoring upstream files at $rRoot\n" >&2
	c=0
	for rFile in $(find -H "$rRoot" -name "*.upstream" -type f);
	do
		oFile=${rFile%.upstream}
		if [ -h $oFile ]; then
			rm "$oFile"
		fi
		mv "$rFile" "$oFile"
		echo "Restored ./${oFile#$rRoot}" >&2
		let c=c+1
	done
	echo -e "\nDone restoring $c files." >&2
	exit 0
elif [ ! -z "$sRoot" -a ! -z "$tRoot" -a -z "$rRoot" ]; then
	echo -e "Linking translation files\nfrom: $sRoot\nto:   $tRoot\n" >&2
	c=0
	for sFile in $(find -H "$sRoot" -type f);
	do
		linkT=${sFile/#$sRoot/$tRoot}
		if [[ -f $linkT || -h $linkT ]]; then
			if ! mv --no-clobber "$linkT" "$linkT.upstream"; then
				echo "Skipping $sFile: Target could not be backed up." >&2
			else
				if ln --symbolic --no-target-directory ${FORCE_LINKS+--force} "$sFile" "$linkT"; then
					echo "Done ${FORCE_LINKS+forced} linking ./${linkT#$tRoot}" >&2
					let c=c+1
				fi
			fi
		else
			echo "Skipping ./${sFile#$sRoot}: doesn't exist in target directory." >&2
		fi
	done
	echo -e "\nDone linking $c files." >&2
	exit 0
fi

show_usage