# settings, target must end in /
backup='/home'
target='/backup'
ssh_user='username'
ssh_server='localhost'

# Create the connection string.
ssh_connect="${ssh_user}@${ssh_server}"

# Check if the ssh connection can be made, a ssh keypair without keyphrase must exist.
ssh -q -q -o 'BatchMode=yes' -o 'ConnectTimeout 3' ${ssh_connect} exit &> /dev/null

if [ $? != 0 ]
then
echo "SSH connection ${ssh_connect} failed."
exit 69 # service unavailable
fi

# check if target exists
if ssh ${ssh_connect} "[ ! -d '${target}' ]"
then
echo "Target '${target}' does not exist, backup stopped."
exit 66 # cannot open input
fi

# Get the current host and append it to target, create a folder for the host if it doesn't exist.
host=`hostname -s`
target="${target}${host}/"

if ssh ${ssh_connect} "[ ! -d '${target}' ]"
then
ssh ${ssh_connect} "mkdir '${target}'"
fi

# Create rotation folders if neccessary.
# Note: this is not a real array since bin/bash can't be used.
folders0='hourly'
folders1='daily'
folders2='weekly'
folders3='monthly'
folders4='yearly'

index=0
max_index=5

while [ ${index} -lt ${max_index} ]
do
eval folder="\${target}\${folders${index}}"

if ssh ${ssh_connect} "[ ! -d '${folder}' ]"
then
ssh ${ssh_connect} "mkdir '${folder}'"
fi

index=`expr ${index} + 1`
done

# Date for this backup.
date=`date '+%Y-%m-%d_%Hh%Mm%Ss'`

# Check and create lockfile.
lockfile=${target}lockfile

if ssh ${ssh_connect} "[ -f '${lockfile}' ]"
then
echo "Lockfile '${lockfile}' already exists, backup stopped."
exit 73 # can't create (user) output file
else
ssh ${ssh_connect} "touch '${lockfile}'"
fi

# -- make backup
# Make the actual backup, note: the first time this is run, the latest folder
# can't be found. rsync will display this but will proceed.
rsync \
--archive \
--xattrs \
--compress \
--human-readable \
--delete \
--link-dest=${target}latest \
${backup} \
${ssh_connect}:${target}${date}-incomplete

# Backup complete, it will be moved to the hourly folder.
ssh ${ssh_connect} "mv ${target}${date}-incomplete ${target}hourly/${date}"
# Create a symlink to new backup .
ssh ${ssh_connect} "ln -s ${target}hourly/${date} ${target}latest-${date}"
# Replace old current symlink with newly created symlink, it's done with mv to
# avoid having a moment where there is no symlink 'current' (-f avoids prompt
# when a target already exists).
ssh ${ssh_connect} "mv -fT ${target}latest-${date} ${target}latest"
# Set the modification moment to now for the new backup, this way, when rotating,
# the time when a backup was finished is used.
ssh ${ssh_connect} "touch ${target}hourly/${date}"

# -- rotate backups
# To determine when to rotate a backup from ie hourly to daily, the latter must
# be checked to see if there is a backup present up until the amount of days
# ago. If there isn't, and the former folder has more then 1 backup, the oldest
# is moved to the latter folder.
rotate1='2' # Rotate the oldest hourly if there is no daily in the last 2 days
rotate2='14' # Rotate the oldest daily if there is no weekly in the last 14 days
rotate3='60' # Rotate the oldest weekly if there is no monthly in the last 60 days (approx. 2 months)
rotate4='730' # Rotate the oldest monthly if there is no yearly in the last 730 days (approx. 2 years)

index=0 # Start with 0, this ways the first from folder can be determined.
max_index=4

while [ ${index} -lt ${max_index} ]
do
eval from="\${target}\${folders${index}}"

# Increase index now so the amount of days and the to folder can be determined.
index=`expr ${index} + 1`

eval days="\${rotate${index}}"
eval to="\${target}\${folders${index}}"

# The -name '20*' is there to limit the files which can be found to everything
# starting with 20*. This means the script only works for the years 2000-2099 but
# this should be enough :).
if [ `ssh ${ssh_connect} "find ${from} -maxdepth 1 -name '20*' | wc -l"` -gt 1 ] && [ `ssh ${ssh_connect} "find ${to} -maxdepth 1 -type d -mtime -${days} -name '20*' | wc -l"` -eq 0 ]
then
oldest=`ssh ${ssh_connect} "ls -1 -tr ${from} | head -1"`
ssh ${ssh_connect} "mv ${from}/$oldest ${to}"
fi

done

# -- delete old backups
# To determine when to delete a backup from ie hourly it must be older then
# the given amount of days. Note, because of this deletion, the rotation is
# done before it.
delete0='0' # Hourly backups older then 1 day are removed.
delete1='7' # Daily backups older then 7 days are removed.
delete2='30' # Weekly backups older then 30 days (approx. 1 month) are removed.
delete3='365' # Monthly backups older then 365 days (approx. 1 year) are removed.
delete4='1095' # Yearly backups older then 1095 days (approx. 3 years) are removed.

index=0
max_index=5

while [ ${index} -lt ${max_index} ]
do
eval from="\${target}\${folders${index}}"
eval days="\${delete${index}}"

ssh ${ssh_connect} "find ${from} -maxdepth 1 -type d -mtime +${days} | xargs rm -rf"

index=`expr ${index} + 1`
done