#!/bin/bash

#
# Cmdline arguments, and they must be in order:
#
# 1: The name of the folder, and only the folder.
#    If you want /var/spool/mail you write mail here.
#
# 2: Remote parent folder, with final /.
#    E.g. root@remote.host:/var/spool/
#    Or rsync://remote.host/var/spool/
#    Or just /var/spool/ if local to local backup.
#
# 3: Parent folder to store the backup, again with /.
#    E.g. /backup/
#
# 4: Number of increments to keep. Defaults to 4.
#
# Examples:
# /usr/bin/incremental.sh mail root@hostname:/var/spool/ /backup/hostname/ 7
# /usr/bin/incremental.sh home root@hostname:/ /backup/hostname/ 7
# /usr/bin/incremental.sh etc rsync://hostname/ /backup/hostname/ 7
#
# The script will exclude files based on an exclude.x file in rsync format.
# In the above home example the exclude file should be:
# /backup/hostname/exclude.home
#
# Going from the home example, the directory structure would after a few
# iterations look akin to:
# /backup/homename/home.0/
# /backup/homename/home.1/
# /backup/homename/home.2/
# /backup/homename/home.std.log.0
# /backup/homename/home.std.log.1
# /backup/homename/home.std.log.2
# /backup/homename/home.err.log.0
# /backup/homename/home.err.log.1
# /backup/homename/home.err.log.2
# /backup/homename/exclude.home
#

let LEVELS="$4"+0
if [ "$LEVELS" -le "0" ]
then
	LEVELS=4
fi

# If target folder doesn't exist, create it.
if [ ! -d "$3" ]
then
	mkdir -p "$3"
	if [ ! -d "$3" ]
	then
		echo "Couldn't create $3!"
		exit
	fi
	chmod 0700 "$3"
fi

cd "$3"

if [ ! -f "exclude.$1" ]
then
	touch "exclude.$1"
	chmod 0600 "exclude.$1"
fi

# If there is a .0 level, shuffle all levels down one
if [ -d "$1.0" ]
then
	if [ -d "$1.$LEVELS" ]
	then
		rm -rf "$1.$LEVELS"
	fi

	if [ -f "$1.std.log.$LEVELS" ]
	then
		rm -f "$1.std.log.$LEVELS"
	fi
	if [ -f "$1.err.log.$LEVELS" ]
	then
		rm -f "$1.err.log.$LEVELS"
	fi

	for ((a=$LEVELS-1,b=$LEVELS ; a>=0 ; a--,b--))
	do
		if [ -d "$1.$a" ]
		then
			mv "$1.$a" "$1.$b"
		fi
		if [ -f "$1.std.log.$a" ]
		then
			mv "$1.std.log.$a" "$1.std.log.$b"
		fi
		if [ -f "$1.err.log.$a" ]
		then
			mv "$1.err.log.$a" "$1.err.log.$b"
		fi
	done
fi

# Capture all output from here on to the specific logs
{
	if [ -d "$1.1" ]
	then
		# If the .1 level exists, consider it the most recent to link against
		rsync -azSvy --partial "--exclude-from=exclude.$1" --numeric-ids --delete --delete-excluded "--link-dest=../$1.1" "$2$1/" "$1.0/"
	else
		# If it doesn't exist, make a full copy into .0
		rsync -azSvy --partial "--exclude-from=exclude.$1" --numeric-ids --delete --delete-excluded "$2$1/" "$1.0/"
	fi
} > "$1.std.log.0" 2> "$1.err.log.0"