#!/bin/sh

set -eu

umask 077

ROTATED=30

CONFDIR="/etc/rsync-backup"
DESTDIR="/srv/backup"
LOGDIR="/var/log/rsync-backup"
RUNDIR="/var/run/rsync-backup"

find_rotated() {
    # sort dailys from oldest to newest, daily.7 daily.6 daily.5 ...
    find "$1" -mindepth 1 -maxdepth 1 -type d -name "daily.*" | sort -V -r
}

rotate_dirs() {
    for host in "$@"; do
        # rotate dailys starting from oldest
        if [ ! -d "${DESTDIR}/${host}" ]; then
            continue
        fi
        find_rotated "${DESTDIR}/${host}" | while read -r dir; do
            ext="${dir##*.}"
            next="${dir%.*}.$((ext+1))"
            mv "$dir" "$next"
        done
    done
    # compress logs over 1 day old
    find "$LOGDIR" -type f -name '*.log' -mtime +1 -execdir gzip -f {} ';'
}

prune_dirs() {
    for host in "$@"; do
        # remove oldest dailys
        find_rotated "${DESTDIR}/${host}" | while read -r dir ; do
            num="$(basename "$dir" | sed -e 's/^daily.//')"
            if [ "$num" -gt $ROTATED ]; then
                rm -rf "$dir"
            fi
        done
    done
    # remove logs over ROTATED*2 days old
    find "$LOGDIR" -type f -name '*.log.gz' -mtime +$((ROTATED*2)) -delete
}

rsync_pull() {
    dirs=""
    opts=""
    host="$1"
    conf="${CONFDIR}/${host}.conf"
    if [ -s "$conf" ] && [ -x "$conf" ]; then
        # shellcheck source=/dev/null
        . "$conf" || return
    else
        echo "skipped: ${1}" 1>&2
        return
    fi

    lockdir="${RUNDIR}/${host}.lock"
    mkdir -m 0755 "$lockdir" || return

    if [ "$host" = "$(hostname)" ]; then
        # skip ssh for localhost
        set -- $dirs
    else
        set -- $(for d in $dirs; do echo "${host}:${d}" ; done)
    fi

    base="${DESTDIR}/${host}"
    if [ ! -d "$base" ]; then
        mkdir -m 0700 "$base" || return
    fi
    dest="${base}/daily.0"
    last="${base}/daily.1"
    if [ ! -d "$dest" ]; then
        mkdir -m 0700 "$dest" || return
    fi
    if [ -d "$last" ]; then
        # hardlink unchanged files to previous daily
	opts="--ignore-existing --link-dest=${last}"
    fi

    logfile="${LOGDIR}/${host}.$(date +%Y%m%d-%H%M%S).log"
    if ! /usr/local/bin/rsync \
        -e "ssh -o BatchMode=yes -i ${CONFDIR}/id_ed25519" \
	-Raqxz --no-devices $opts \
        --log-file="$logfile" \
	"$@" "$dest"
    then
        echo "rsync log: ${logfile}" 1>&2
    fi
    rmdir "$lockdir"
}

if [ ! -d "$DESTDIR" ]; then
    echo "ERROR: ${DESTDIR} does not exist" 1>&2
    exit 1
fi

if [ ! -d "$LOGDIR" ]; then
    echo "ERROR: ${LOGDIR} does not exist" 1>&2
    exit 1
fi

if [ ! -d "$RUNDIR" ]; then
    mkdir -m 0755 "$RUNDIR"
fi

ALL=false
PRUNE=false
ROTATE=false
while getopts "apr" OPT; do
    case "$OPT" in
        a)
            ALL=true
            ;;
        p)
            PRUNE=true
            ;;
        r)
            ROTATE=true
            ;;
        *)
            echo "Usage: $(basename "$0") [-apr] [host ...]" 1>&2
            exit 1
            ;;
    esac
done
shift $((OPTIND-1))

mkdir -m 0755 "${RUNDIR}/daily.lock"
trap 'rmdir "${RUNDIR}/daily.lock"' EXIT

if [ $ALL ]; then
    for conf in "${CONFDIR}"/*.conf ; do
        host="$(basename "$conf" ".conf")"
        set -- "$host" "$@"
    done
fi

$ROTATE && rotate_dirs "$@"

for host in "$@" ; do
    rsync_pull "$host"
done

$PRUNE && prune_dirs "$@"