#!/bin/bash
#
# rsync-backup.sh - a backup script using rsync.
#
# Copyright 2015 - 2018 Einhard Leichtfuß
#
# This file is part of rsync-backup.
#
# rsync-backup is free software: you can redistribute it and/or modify
# it under the terms of the GNU Affero General Public License as published
# by the Free Software Foundation, either version 3 of the License, or
# (at your option) any later version.
# 
# rsync-backup is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
# GNU General Public License for more details.
# 
# You should have received a copy of the GNU Affero General Public License
# along with rsync-backup.  If not, see <https://www.gnu.org/licenses/>.
#

RSYNC=rsync

typeset -a rsync_args
typeset -a rsync_inc_args
typeset -A bakpath
typeset filter_file_all			# Applied after specific filter.
typeset -A filter_file

# Default arguments for rsync (-rptogAXlHS, --timeout, --info).
rsync_args=(
	--recursive
	--perms --times --owner --group
	--acls --xattrs
	--links
	--hard-links
	--sparse
	--timeout=60
	#-vv
	--info=progress2
	)

# Supplemental arguments for rsync; only used when an actual incremental
# update is performed, i.e. when --link-dest is used.
rsync_inc_args=(
	--fuzzy --fuzzy
	)

filter_file_all=/etc/rsync-backup/filter

config=/etc/rsync-backup/backup.conf
source "$config"

src=/home/respiranto/txt/bash/rsync-backup/src
dest=/home/respiranto/txt/bash/rsync-backup/dest

typeset -l reply
typeset -i i n

# RSYNC args.
# basic args:  --recursive --perms --times --owner --group --links
# extra args:  --sparse --acls --xattrs --hard-links --timeout=60
#              --fuzzy --fuzzy
#              --filter="merge <file>"
# likely:      --compress
#              --partial{,dir=DIR}
#              --progress
# possibly:    --devices --specials
#              --max-size=SIZE-OF-FILE
#              --one-file-system
#              --log-file=FILE --log-file-format=FORMAT
#              --human-readable
# unlikely:    --omit-{dir,link}-times --update (!--inplace) --delete
#              --exclude
# great:       --link-dest=DIR (timestamps?)
# testing:     --verbose --dry-run (-vn)
# interesting: --sockopts --itemize-changes --out-format=FORMAT
#              --stats

function main
{
	# In case of a non-matching wildcard, return nothing.
	shopt -s nullglob
	# Include dotfiles (except . and ..) in regex matching.
	shopt -s dotglob

	get_args "$@" || return $?

	check_paths || return $?

	# Change the separation char to $'\n' to avoid confusion with filenames
	# containing spaces (default is $' \t\n').
	IFS=$'\n'

	find_existing_backup_dirs || return $?

	perform_backup || return $?

	refresh_symlinks || return $?
}


function get_args
{
	if [ $# -eq 0 ]
	then
		echo "Usage: $0 <src> [<dest>]"
		return 1
	fi

	dirpath="$(realpath "$1")"

	if [ $# -gt 1 ]
	then
		bakpath="$(realpath $2)"
	elif test -v bakpath[$dirpath]
	then
		bakpath="${bakpath[$dirpath]}"
	else
		echo "Error: Backup path for $dirpath not configured."
		return 1
	fi

	filter_args=()
	if test -v filter_file[$dirpath] && test -f "${filter_file[$dirpath]}"
	then
		filter_args+=("--filter=merge ${filter_file[$dirpath]}")
	fi
	if test -v filter_file_all -a -f "$filter_file_all"
	then
		filter_args+=("--filter=merge ${filter_file_all}")
	fi
}


function check_paths
{
	# Test whether the dirs exist already.
	if ! test -d "$dirpath"
	then
		echo "Source (\"$dirpath\") does not exist."
		return 1
	fi

	if ! test -d "$bakpath"
	then
		echo "Target (\"$bakpath\") does not exist."
		echo -n "Do you want do create it [y/N]? "
		read reply
		if [[ "$reply" != "y" && "$reply" != "yes" ]]
		then
			return 1
		fi

		if ! mkdir -p "$bakpath"
		then
			echo "Backup creation has failed."
			echo "\"$bakpath\" could not be created."
			return 1
		fi
	fi
}


function find_existing_backup_dirs
{
	n=0
	for file in `ls "$bakpath"`; do
		if test -d $bakpath/$file \
			&& [[ "$file" =~ ^[0-9]{4}-[0-1][0-9]-[0-3][0-9]_[0-2][0-9]([0-5][0-9]){2}.backup$ ]]
		then
			dirs[n]="$file"
			n+=1
		fi
	done
}


# $1 path
# $2 error message: string
function clear_file
{
	if test -e "$1" -o -L "$1"; then
		echo "It seems like the last backup process failed or you have created" \
		 	"the file \"$1\" manually."
		echo -n "Do you want to delete it [y/N]? "
		read reply
		if [[ "$reply" == "y" || "$reply" == "yes" ]]
		then
			printf "Deleting"
			if rm -rf "$1"; then
				printf " - done\n"
				return 0
			else
				printf '\n%s\n' "$2"
				printf 'The file \"%s\" could not be deleted.\n' "$1"
				return 1
			fi
		else
			printf '%s\n' "$2"
			printf '%s %s\n' "Please remove the above mentioned file manually" \
				"or run this script once more."
			return 1
		fi
	fi
	return 0
}


function perform_backup
{
	bakdate=`date +%Y-%m-%d_%H%M%S.backup`
	finaldir="$bakpath/$bakdate"
	tempdir="$bakpath/new.backup"
	clear_file "$tempdir" "Backup creation has failed." || return 1
	clear_file "$finaldir" "Backup creation has failed." || return 1

	# note: $n == ${#dirs[@]}
	printf 'Starting backup nr. %u.\n' "$n"
	if [ $n -eq 0 ]
	then
		# Perform first backup, not incremental.
		$RSYNC "${rsync_args[@]}" \
			"${filter_args[@]}" \
			"$dirpath"/ "$tempdir" \
			|| return 1
	else
		# Perform incremental backup on the basis of the last.
		$RSYNC "${rsync_args[@]}" \
			"${rsync_inc_args[@]}" --link-dest="${bakpath}/${dirs[n-1]}" \
			"${filter_args[@]}" \
			"$dirpath"/ "$tempdir" \
			|| return 1
	fi

	mv "$tempdir" "$finaldir" || return 1
	printf '\nCreating of backup nr. %u succesfully executed.\n' "$n"
}


function refresh_symlinks
{
	linkdir="$bakpath/latest"
	if test -L "$linkdir"
	then
		rm "$linkdir"
		ln -s "$bakdate" "$linkdir"
	elif clear_file "$linkdir" "Creation of softlink \"$linkdir\" failed."
	then
		ln -s "$bakdate" "$linkdir"
	fi

	# by_number
	numdir="$bakpath/by_number"
	if ! test -d "$numdir"
	then
		if clear_file "$numdir" "Creating directory $numdir failed."
		then
			mkdir "$numdir"
		else
			return 1
		fi
	fi

	for file in "$numdir"/*
	do
		if test -L "$file"
		then
			rm "$file"
		else
			if ! clear_file "$file" "Setting up numbered softlinks failed."
			then
				return 1
			fi
		fi
	done

	dirs[$n]="$bakdate" # Set last dir on current.

	max_digits=${#n}
	zeros[max_digits]=''
	i=$max_digits-1
	while [ $i -ge 1 ]
	do
		zeros[i]=${zeros[i+1]}0
		i+=-1
	done

	i=0
	while [ $i -le $n ]
	do
		ln -s "../${dirs[i]}" "$numdir/${zeros[${#i}]}$i"
		i+=1
	done
}


main "$@"