rollback

#!/bin/bash

set -u
set -e

_ROLLBACKS=()

_doRoll()
{
	set +e

	local WHAT=("$@")

	for ((i=${#WHAT[@]}-1; i >= 0; i--));
	do
		CMD=${WHAT[i]}

		eval "$CMD;"

		if [ $? -ne 0 ];
		then
			>&2 echo "Command failed: $CMD"
			>&2 echo "# Rollback commands:"

			for ((k=${#_ROLLBACKS[@]}-1; k >= 0; k--));
			do
				eval 'local R=("${'"${_ROLLBACKS[k]}"'_ROLLBACK[@]-"# none"}")'

				>&2 echo "# ${_ROLLBACKS[k]}"

				for ((j=${#R[@]}-1; j >= 0; j--));
				do
					>&2 echo "${R[j]}"
				done
			done

			>&2 echo "# Teardown commands:"

			for ((k=${#_ROLLBACKS[@]}-1; k >= 0; k--));
			do
				eval 'local R=("${'"${_ROLLBACKS[k]}"'_TEARDOWN[@]-"# none"}")'

				>&2 echo "# teardown: ${_ROLLBACKS[k]}"

				for ((j=${#R[@]}-1; j >= 0; j--));
				do
					>&2 echo "${R[j]}"
				done
			done

			exit 1
		fi
	done
}

_saveTeardown()
{
	local NAME=$1
	local WHERE=$2

	shift 2

	local WHAT=("$@")

	echo "Saving $NAME teardown commands to $WHERE"

	cat <<EOF > $WHERE
#!/bin/bash

set -u
set -e

EOF

	for ((i=${#WHAT[@]}-1; i >= 0; i--));
	do
		cat <<< "${WHAT[i]}" >> $WHERE
	done

	chmod +x $WHERE
}

createRollback()
{
	NAME=$1

	_ROLLBACKS+=("$NAME")

	eval "${NAME}_ROLLBACK=()"
	eval "${NAME}_TEARDOWN=()"
	eval "${NAME}_STATUS=0"

	eval "$2"'() { '"$NAME"'_ROLLBACK+=("$*"); }'

	if [ -n "$4" ];
	then
		eval "$4"'() { '"$NAME"'_TEARDOWN+=("$*"); }'

		if [ -n "$5" ];
		then
 			eval "$5"'() { '"$2"' "$*"; '"$4"' "$*"; }'
		fi
	fi

	eval "$NAME"'() { >&2 echo "Encountered an error in '"$NAME"', rolling back"; _doRoll "${'"$NAME"'_ROLLBACK[@]}"; '"$NAME"'_STATUS=1; }'
	eval "$3"'() { echo "Finished in '"$NAME"', running teardown"; _doRoll "${'"$NAME"'_TEARDOWN[@]}"; }'

	if [ -n "$6" ];
	then
		eval "$6"'() { _saveTeardown "'"$NAME"'" "$1" "${'"$NAME"'_TEARDOWN[@]}"; }'
	fi
}