#!/bin/bash
#
# Duplicity Control Tool -- description at far below (after "exec duplicity")

if [ $# -lt 2 ] ; then
    cat <<EOF >&2
** Usage: dupltool [options] source url
** Source directory and store url are required, and the url
** MUST be of form "pexpect+scp:/\$HOST/\$REMOTEDIR"
EOF
    exit 1
fi

#-- Grab command line arguments 
DUPL=( $* )
STORE="${DUPL[-1]}"
SOURCE="${DUPL[-2]}"

#-- Confirm that the STORE url was of expected format

if [ -n "${STORE##pexpect+scp:/*/*}" ] ; then
    echo "** Bad store URL: $STORE" >&2
    echo "** Required format: pexpect+scp:/$HOST/$REMOTEDIR" >&2
    exit 1
fi

## Helper function to read duplicity pathnames and prefix them with
## their from and to months, as in ${FROM}${TO}:${FILENAME}
## both $FROM and $TO are 6 digits (yyyymm).
remote_from_to_month_prefix() {
    sftp $SFTP <<< "ls" | while read F ; do
	case "$F" in
	    duplicity-full-signatures.*) echo "${F:26:6}${F:26:6}:$F" ; ;;
	    duplicity-full.*) echo "${F:15:6}${F:15:6}:$F" ; ;;
	    duplicity-inc.*) echo "${F:14:6}${F:34:6}:$F" ; ;;
	    duplicity-new-signatures.*) echo "${F:25:6}${F:45:6}:$F" ; ;;
	esac
    done | sort -r
}

THISMONTH="$(date -u "+%Y%m")" # UTC date

SFTP="${STORE##pexpect+scp://}"
HOST="${SFTP%%/*}"
REMOTEDIR="${SFTP#*/}"
SFTP="sftp://$SFTP" # openssh-client=1:8.4p1-5+deb11u1
#SFTP="$HOST:$REMOTEDIR" # openssh-client=1:7.6p1-4ubuntu0.7

# Obtain remote pathnames with from-to prefix in reverse date order,
# i.e., newest first.
FILES=( $(remote_from_to_month_prefix) )

if [ -n "$FILES" ] ; then
    THATMONTH="${FILES[0]:0:6}" # to-month of newest
    if [ "$THISMONTH" != "$THATMONTH" ] ; then
	echo "** New monthly snapshot; stashing daily into .$THATMONTH" >&2
	{ # Generate command stream for sftp
	    echo "mkdir .$THATMONTH"
	    FX=
	    for F in ${FILES[@]} ; do
		[ "${F:0:6}" != "$THATMONTH" ] && break
		[ -n "$FX" ] && echo "rename $FX .$THATMONTH/$FX"
		FX="${F#*:}"
		[ -z "${FX%duplicity-full*}" ] && break
	    done
	} | sftp $SFTP
	echo "** Stashing into .$THATMONTH completed" >&2
    fi
fi

exec duplicity ${DUPL[@]}
exit 1 # jic

# Duplicity Control Tool
# ======================
#
# This Duplicity Control Tool should be run as a daily anacron job (or
# daily as a cron job) so as to make regular snapshots of a directory
# tree using duplicity with the pexpect+scp backend.
#
# Ideally the backup store should be set up with password-less scp
# access, preferrably as a non-root remote user, or at the very least
# be accessed by means of a local ssh-agent.
#
# The store is then managed by this Duplicity Control Tool to keep a
# multi-level history, which ends up as a succession of monthly
# snapshots with a most recent tail of daily snapshots. Specifically,
# at the first snapshot event each month, the store is revised by
# stashing away the snapshots of the most recent previous month, to
# leave the first one (or the most recent full) as the start point for
# a new snapshot, which thus becomes a "monthly" snapshot.
#
# The chain of daily snapshots from that first (monthly or full)
# snapshot remain stashed in the ".%Y%m" directory.
#
# Note that the Duplicity Control Tool considers "the month of the
# last snapshot or full" to be "the previous month" regardless of how
# many months back from today that might be, i.e., it will stash
# snapshots just as if that month was the prior month. In other words,
# if you would happen to have a huge temporal hole in the snapshot
# series you might consider running a plain duplicity snapshot first
# and then let the subsequent, regular runs of the Duplicity Control
# Tool build its multi-level snapshot history henceforth.
#
# === These are the examples of the various duplicity snapshot files:
# duplicity-full.20230128T010719Z.vol1.difftar.gz
# duplicity-full-signatures.20230128T010719Z.sigtar.gz
# duplicity-new-signatures.20221216T230345Z.to.20221217T230403Z.sigtar.gz
# duplicity-inc.20230128T010719Z.to.20230130T082241Z.manifest
# duplicity-inc.20230127T061825Z.to.20230130T081002Z.vol1.difftar.gz