#!/bin/bash

# Script to perform incremental backups using rsync
# It is often ran as crontab rule for automated backup solution
#
# This script will respect .rsync-filter files, which can be used
# to define custom exclude rules for files/dirs in which it is present

if [ $# -lt 2 ]; then
  echo "Invalid amount of arguments passed!"
  echo "Arguments: <Source path> <Backup path> [--note]"
  echo "  <Source path>: directory to be backed up, usually '/'"
  echo "  <Backup path>: directory to back up to (destination), usually mounted drive"
  exit
fi

SOURCE_DIR="$1"
BACKUP_DIR="$2"
DATETIME="$(date '+%Y-%m-%d_%H:%M:%S')"
BACKUP_PATH="${BACKUP_DIR}/${DATETIME}"
LATEST_LINK="${BACKUP_DIR}/latest"
NOTE_FILE="${BACKUP_PATH}/note.md"

mkdir -p "$BACKUP_DIR"

rsync -avHAXS \
  --delete \
  --filter='dir-merge /.rsync-filter' \
  --link-dest "${LATEST_LINK}" \
  "${@:3}" "${SOURCE_DIR}/" "${BACKUP_PATH}"

# Only attempt to override the symlink if we made new backup_path
# user might've passed --dry-run option in which case we wouldn't
# want to override latest symlink to non-existent location
if [ -d "${BACKUP_PATH}" ]; then
  rm "${LATEST_LINK}" 2>/dev/null
  ln -s "$(basename "$BACKUP_PATH")" "${LATEST_LINK}"
fi

# Lastly, open a note file with $EDITOR insite of the backup dir,
# so the user can put in any personal notes about this backup (such
# as reason it was made, making it easy to identify it).
#
# If this command is ran with sudo (like for system wide backups),
# open the note file with user's editor, not root's
if [ "${SUDO_USER:-$USER}" != "$USER" ]; then
  # Run command as the original user via sudo, with -s argument, to
  # also load the user's shell, so the user's env variables ($EDITOR)
  # gets set. Then make the user run sudoedit, opening a temp file,
  # which when saved, will get written to the note file as user we're
  # sudoed as. Note: this will re-prompt for sudo password.
  NOTE_FILE="$NOTE_FILE" sudo -s --preserve-env="NOTE_FILE" -u "$SUDO_USER" sh -c 'sudoedit -u "$SUDO_USER" "$NOTE_FILE"'
else
  $EDITOR "$NOTE_FILE"
fi