#!/bin/bash

## A user callback for backintime
## Copyright 2021 Fancesco Potortì, released under AGPL 3.0 or later version
##
## Return 0 if everything is alright.
## Any other return code cancels the running snapshot

################################################################
## User variables

PATH=/bin:/sbin:/usr/bin:/usr/sbin

## It is possible to store the backup files on a volume which is mounted before the backup and
## unmounted afterwards.  If this is what you do, then set the following variables
mount_point=			# leave blank if no mounting and unmounting is necessary
mount_point=/backup		# the mount point for storing the backup files
if [ "$mount_point" ]; then
    ## The device to mount for storing the backup files
    mount_dev=			# leave blank if reading device from fstab
    mount_dev=$(/usr/sbin/findfs LABEL=backup)
    ## The options used when mounting the device
    mount_opts=			# leave blank if reading options from fstab
    mount_opts="-o barrier,compress=zstd:15"
fi

## Log
maxlogs=40
## TODO: log options: short or long log, send email, store to /var/log/


################################################################
## Internal variables and code

## Parameters
profile_id="$1"
profile_name="$2"
reason="$3"

local_dir=$HOME/.local/share/backintime/	# where the log file resides
shortlog=$local_dir/shortlog			# short log of the backup process
tmplog=$local_dir/tmplog-$PPID
size_file=$local_dir/init-size-$PPID

((running_under_schedule = (SHLVL == 1)))

function print_free_space () {
    ## Indent df output by two spaces
    df --sync --human-readable --output=target,ipcent,used,avail,pcent $mount_point | sed 's/^/  /'
    echo
}

case $reason in
    1) ## Backup process begins
	if ((running_under_schedule)); then	# running under Cron
	    rm --force $tmplog
	fi
	;;
esac

if ((running_under_schedule)); then		# running under Cron
    exec &>>$tmplog		# all output goes to the tmplog file
fi
    
case $reason in
    1) ## Backup process begins
	date; echo
	echo "- Backup process begins"

	if [ "$mount_point" ]; then
	    ## Store initial filesystem size
	    df --sync --block-size=1M --output=used $mount_point | tail -1 > $size_file
	    print_free_space
	fi
        ;;
    
    2) ## Backup process ends
	echo "- Backup process ends"

	## Read takesnapshot_.log, excluding all lines containing 'BACKINTIME' and including
	## only lines starting with '[I] ', remove the '[I] ' and indent by two spaces
	sed -n '/BACKINTIME/d; /Smart remove/d; /^\[I] /s//  /p' $local_dir/takesnapshot_.log

	if [ "$mount_point" ]; then
	    ## Check file system
	    echo -n "  Checking file system..."
	    mount -o remount,ro $mount_point
	    fstype=$(df --output=fstype $mount_point | tail -1)
	    device=$(df --output=source $mount_point | tail -1)
	    case $fstype in
		btrfs)
		    ## --mode lowmem on an SSD 1TB filesystem increases checking time from 8
		    ## to 180 minutes and decreases resident memory occupancy from 7 to 5 GB
		    #fsck="btrfs check --force --check-data-csum --mode lowmem"
		    fsck="btrfs check --force --check-data-csum"
		    ;;
		ext*)
		    fsck="fsck -T -pf -t ext2"
		    ;;
		*)
		    fsck="fsck -T"
		    ;;
	    esac
	    chkout=$($fsck $device 2>&1)
	    chkret=$?
	    if ((chkret == 0)); then
		echo " success"
	    else
		if ((chkret == 137)); then
		    echo " FAILED: killed by the oom killer"
		    echo "Not enough memory available at the moment"
		else
		    echo " FAILED: $fsck $device returned $chkret"
		    echo $chkout
		fi
	    fi

	    print_free_space

	    ## Compute used space
	    isz=$(cat $size_file)
	    fsz=$(df --block-size=1M --output=used $mount_point | tail -1)
	    echo "  ${fsz}-${isz} = *** $((fsz-isz)) MB used ***"
	    rm --force $size_file
	fi
	
	echo; date
	if ((running_under_schedule)); then	# running under Cron
	    if command -v mailx &>/dev/null; then
		mailx -s backintime $LOGNAME < $tmplog
	    fi
	    if command -v savelog &>/dev/null; then
		savelog -lc $maxlogs  $shortlog
	    fi
	    mv $tmplog $shortlog
	fi
        ;;
    
    3) ## A new snapshot was taken
        snapshot_id="$4"
        snapshot_name="$5"
	echo -e "- A new snapshot $snapshot_id was taken"
        ;;

    4) ## There was an error
        errorcode="$4"
	echo "- Signaling error code $errorcode"
        case $errorcode in
            1) ## ERROR The application is not configured
		msg="ERROR The application is not configured"
		;;
            2) ## ERROR A 'take snapshot' process is already running
		msg="ERROR A 'take snapshot' process is already running"
		;;
            3) ## ERROR Can't find snapshots folder (is it on a removable drive ?)
		msg="ERROR Can't find snapshots folder (is it on a removable drive ?)"
		;;
            4) ## ERROR A snapshot for 'now' already exist
		msg="ERROR A snapshot for 'now' already exist"
		;;
	    *) ## ERROR Unknown error
		msg="ERROR Unknown error, probably this callback handler is outdated"
		;;
        esac
	echo "$msg"
        ;;

    5) ## backintime-qt4 (GUI) started
	echo "- GUI started"
        ;;

    6) ## backintime-qt4 (GUI) closed
	echo "- GUI closed"
        ;;

    7) ## Mount drives
	echo "- Mounting drives"
	if [ "$mount_point" ]; then
	    echo "Mounting $mount_point"
            umount $mount_point 2> /dev/null || true
	    mount $mount_opts $mount_dev $mount_point
	fi
	;;

    8) ## Unmount the drives
	echo "- Unmounting drives"
	if [ "$mount_point" ]; then
	    echo "Unmounting $mount_point"
            umount $mount_point 2> /dev/null || true
	fi
	;;

    *) ## Unknown reason
	echo "- Unknown callback reason, probably this callback handler is outdated"
	;;
    
esac