##
# systr_rsync_normal <src> <dst> [<link>]
#
# Perform normal rsync operations to transfer files to or from the
# repository.  If <link> is set, it is used as the --link-dest value.
##
function systr_rsync_normal
{
    if [ $# -lt 2 ]; then
        echo "Fatal: too few args to rsync_normal" >&2
        exit 1
    fi

    src="$1"
    dst="$2"

    if [ $# -gt 2 ]; then
        link="--link-dest=$3"
    else
        link=""
    fi

    rsync -az --info=progress2 --info=stats2 --delete \
        --exclude='*.systr' $link "$src" "$dst"
}

##
# systr_rsync_diff <src> <compare> <dst>
#
# Copy files from <src> to <dst>, but only if they've changed
# since the state in <compare>.  Empty directories are
# purged from <dst> afterward.
##
function systr_rsync_diff
{
    if [ $# -lt 3 ]; then
        echo "Fatal: too few args to rsync_diff" >&2
        exit 1
    fi

    src="$1"
    compare="--compare-dest=$2"
    dst="$3"

    rsync -az --delete --exclude='*.systr' $compare \
        "$src" "$dst"

    find "$dst" -type d -empty -delete
}

##
# systr_rsync_del <src> <compare> <dst>
#
# Delete files in <dst>, only if they have been deleted from
# <compare> to <src>.  Deleted files in <dst> are 'backed up',
# in rsync lingo, meaning they are actually renamed with a
# suffix appended to the original filename.
#
# If <src> is the worktree ("."), our file suffix will be
# '&' to signify files deleted by us.  Otherwise, the suffix
# will be '~' to signify files deleted by 'them'.
##
function systr_rsync_del
{
    if [ $# -lt 3 ]; then
        echo "Fatal: too few args to rsync_del" >&2
        exit 1
    fi

    src="$1"
    compare="--compare-dest=$2"
    dst="$3"

    if [[ "$src" == "." ]]; then
        suffix="--suffix='&'"
    else
        suffix="--suffix='~'"
    fi

    rsync -azb $suffix --existing --ignore-existing \
        --delete --exclude='*.systr' $compare \
        "$src" "$dst"
}

##
# systr_rsync_merge <src> <dst>
#
# Finish setting up a merge, by copying files from the
# temporary directory to the merge staging directory.
#
# Files in <dst> overwritten by this operation will
# be suffixed with '*' to signify files modified by
# both of us.
##
function systr_rsync_merge
{
    if [ $# -lt 2 ]; then
        echo "Fatal: too few args to rsync_merge" >&2
        exit 1
    fi

    src="$1"
    dst="$2"

    rsync -azb --suffix='*' --exclude='*.systr' \
        "$src" "$dst"
}