#!/bin/bash
# backup.sh - Backup directory to compressed tar archive
# 
# Copyright (C) 2025 Coffey Labs
# 
# This program is free software: you can redistribute it and/or modify it 
# under the terms of the GNU General Public License as published by the 
# Free Software Foundation, version 3 of the License.
# 
# This program is distributed in the hope that it will be useful, but 
# WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY 
# or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License 
# for more details.
# 
# You should have received a copy of the GNU General Public License along 
# with this program. If not, see <https://www.gnu.org/licenses/>.
# 
# Usage: backup.sh <source_directory> <destination_directory>
# Description: Creates a tar.gz archive of the source directory in the destination.

set -euo pipefail

SRC="${1:-}"
DEST="${2:-}"
if [ -z "$SRC" ] || [ -z "$DEST" ]; then
  echo "Usage: $0 <source_directory> <destination_directory>"
  exit 1
fi
if [ ! -d "$SRC" ]; then
  echo "Source directory '$SRC' not found!"; exit 1
fi
if [ ! -d "$DEST" ]; then
  # create destination dir if it doesn't exist
  mkdir -p "$DEST" || { echo "Failed to create destination '$DEST'"; exit 1; }
fi

base_name="$(basename "$SRC")"
# Seconds, not just the date. The old %Y%m%d name meant a second run on
# the same day silently overwrote the first -- losing a good backup at
# the exact moment someone was trying to take another one.
date_str="$(date +%Y%m%d-%H%M%S)"
archive_name="${base_name}-backup-${date_str}.tar.gz"
archive_path="$DEST/$archive_name"

if [ -e "$archive_path" ]; then
  echo "Refusing to overwrite existing archive: $archive_path"
  exit 1
fi

# Write to a partial name and rename only on success, so an interrupted
# run cannot leave a truncated file sitting there looking like a backup.
tmp_path="${archive_path}.partial"
trap 'rm -f -- "$tmp_path"' EXIT

if tar -czf "$tmp_path" -C "$(dirname "$SRC")" "$base_name"; then
  mv -- "$tmp_path" "$archive_path"
  trap - EXIT
  echo "Backup successful: $archive_path"
  ls -lh -- "$archive_path"
else
  echo "Backup failed for $SRC" >&2
  exit 1
fi