BACKUP_DIR=${HOME}/.local/config_backup

# list_clones
#
# list cloned files
# print a tab separated file pair (original file, clonded file)
#
# /mandatory
# @param 1: directory of original file
# @param 2: directory of clones
list_clones () {
    ORIG=$1
    CLONE=$2
    if [ -z "$1" -o -z "$2" ]; then return; fi

    find "${CLONE}/" -maxdepth 1 -mindepth 1 -type f | while read f; do
        filename=$( basename "${f}" )
        if [ -f "${ORIG}/${filename}" ]; then
            echo -e "${ORIG}/${filename}\t${f}"
        fi
    done
}

# list_file_pairs
#
# list files where a clone exists
# print a tab separated file pair (original file, clonded file)
list_file_pairs () {
    # /usr/lib vs. /etc
    ORIG=/usr/lib
    CLONE=/etc
    for d in udev/rules.d
        do
        list_clones "${ORIG}/${d}" "${CLONE}/${d}"
    done

    # /usr/share vs. /etc
    ORIG=/usr/share
    CLONE=/etc
    for d in eg25-manager
        do
        list_clones "${ORIG}/${d}" "${CLONE}/${d}"
    done
}

# create_dir
#
# create a (sub)-directory if it does not exist
#
# /mandatory
# @param 1: directory name
create_dir () {
    dir=$1
    echo "${dir}" | grep -q '/../'
    result=$?
    if [ ${result} -eq 0 ]; then
        echo "directory must not contain .."
        exit 1
    fi
    [ -d "${dir}" ] || mkdir -p "${dir}"
}

# main
#
# the main program
main () {
    list_file_pairs | while read pair; do
        orig_file=$( echo "${pair}" | awk -v FS='\t' '{print $1}' )
        clone_file=$( echo "${pair}" | awk -v FS='\t' '{print $2}' )
        diff -q "${orig_file}" "${clone_file}" > /dev/null
        result=$?
        if [ ${result} -ne 0 ]; then
            create_dir $( dirname "${BACKUP_DIR}/${orig_file}" )
            if [ ! -f "${BACKUP_DIR}/${orig_file}" ]; then
                cp "${orig_file}" "${BACKUP_DIR}/${orig_file}"
            else
                diff -q "${orig_file}" "${BACKUP_DIR}/${orig_file}" > /dev/null
                result=$?
                if [ ${result} -ne 0 ]; then
                    echo "## config file \"${orig_file}\" changed, see diff below"
                    diff -u "${BACKUP_DIR}/${orig_file}" "${orig_file}"
                    echo "## remove backup file \"${BACKUP_DIR}/${orig_file}\" after checking the impact"
                    echo -e "\n\n"
                fi
            fi
        fi
    done
}

main