#!/bin/bash
#
# Backups the configuration files of this docker-composed service.
# This is a general purpose worker script, doesn't requires customization.
#
# Author: Kovács Zoltán <kovacs.zoltan@smartfront.hu>
# License: GNU/GPL v3+ (https://www.gnu.org/licenses/gpl-3.0.en.html)
# 2021-09-03 v0.1 Initial release

# Accepted environment variables and their defaults.
PAR_BASEDIR=${PAR_BASEDIR:-""}                  # Service's base folder
PAR_BACKUPDIR=${PAR_BACKUPDIR:-""}              # Folder to dump within

# Other initialisations.
BACKUPDIR="storage/backups/tarballs"            # Folder to dump within
USER=${USER:-LOGNAME}                           # Fix for cron enviroment only
YMLFILE="docker-compose.yml"

# Messages.
MSG_MISSINGDEP="Fatal: missing dependency"
MSG_MISSINGYML="Fatal: didn't find the docker-compose.yml file"
MSG_NONWRITE="The target directory isn't writable"

# Checks the dependencies.
TR=$(which tr 2>/dev/null)
if [ -z "$TR" ]; then echo "$MSG_MISSINGDEP tr."; exit 1 ; fi
for item in date dirname hostname readlink tar
do
    if [ -n "$(which $item)" ]
    then export $(echo $item | "$TR" '[:lower:]' '[:upper:]' | "$TR" '-' '_')=$(which $item)
    else echo "$MSG_MISSINGDEP $item." >&2; exit 1; fi
done

# Where I'm?
# https://gist.github.com/TheMengzor/968e5ea87e99d9c41782
SOURCE="$0"
while [ -h "$SOURCE" ]; do
    # resolve $SOURCE until the file is no longer a symlink
    SCRPATH="$( cd -P "$("$DIRNAME" "$SOURCE" )" && pwd )" #"
    SOURCE="$("$READLINK" "$SOURCE")"
    # if $SOURCE was a relative symlink, we need to resolve it
    # relative to the path where the symlink file was located
    [[ $SOURCE != /* ]] && SOURCE="$SCRPATH/$SOURCE"
done; SCRPATH="$( cd -P "$("$DIRNAME" "$SOURCE" )" && pwd )" #"

# Searches the base folder, containing a docker-compose.yml file.
# Called from the base folder (./)?
BASE_DIR="$PAR_BASEDIR"
TEST_DIR="$SCRPATH"
[[ -z "$BASE_DIR" ]] && [[ -r "$TEST_DIR/$YMLFILE" ]] && BASE_DIR="$TEST_DIR"
# Called from ./tools?
TEST_DIR="$("$DIRNAME" "$TEST_DIR")"
[[ -z "$BASE_DIR" ]] && [[ -r "$TEST_DIR/$YMLFILE" ]] && BASE_DIR="$TEST_DIR"
# Called from ./tools/*.d?
TEST_DIR="$("$DIRNAME" "$TEST_DIR")"
[[ -z "$BASE_DIR" ]] && [[ -r "$TEST_DIR/$YMLFILE" ]] && BASE_DIR="$TEST_DIR"
# On failure gives it up here.
if [ -z "$BASE_DIR" -o ! -r "$BASE_DIR/$YMLFILE" ]; then
    echo "$MSG_MISSINGYML" >&2; exit 1
fi
# Sets the absolute paths.
BACKUPDIR="${PAR_BACKUPDIR:-$BASE_DIR/$BACKUPDIR}"

# The dump target folder must be writable.
[[ ! -w "$BACKUPDIR" ]] \
&& echo "$MSG_NONWRITE: $BACKUPDIR" >&2 && exit 1

# Tries the FS backup.
if [ -w "$BACKUPDIR" ]; then
    BACKUP_NAME="configs.$("$DATE" '+%Y%m%d_%H%M%S').$("$HOSTNAME")"
    ( cd "$BASE_DIR"
      "$TAR" czf "$BACKUPDIR/$BACKUP_NAME.tgz" \
             "$YMLFILE" configs docker \
	     2>>"$BACKUPDIR/$BACKUP_NAME.log"
    )
fi

# That's all, Folks! :)