#!/bin/bash

usage() {
  cat <<EOF
Create a btrfs snapshot

Usage btrfs-backup <subvolume> <backup_dir> [options]

Will create a snapshot of given subvolume in given backup_dir.

Options:
-h | --help: Display this message
-t | --total: Total amount of allowed backups in the same backup_dir
-n | --name: Name of the snapshot (appended after date)

Example for crontab (/etc/crontab):
15,30,45 * * * * 	 root 	 /usr/local/bin/btrfs-backup /.btrfs/@ /.btrfs/@snapshots/@/quaterly --total 4
15,30,45 * * * * 	 root 	 /usr/local/bin/btrfs-backup /.btrfs/@home /.btrfs/@snapshots/@home/quaterly --total 4
15,30,45 * * * * 	 root 	 /usr/local/bin/btrfs-backup /.btrfs/@data /.btrfs/@snapshots/@data/quaterly --total 4
15,30,45 * * * * 	 root 	 /usr/local/bin/btrfs-backup /.btrfs/@log /.btrfs/@snapshots/@log/quaterly --total 4

0 * * * * 	root 	 /usr/local/bin/btrfs-backup /.btrfs/@ /.btrfs/@snapshots/@/hourly --total 8
0 * * * * 	root 	 /usr/local/bin/btrfs-backup /.btrfs/@home /.btrfs/@snapshots/@home/hourly --total 8
0 * * * * 	root 	 /usr/local/bin/btrfs-backup /.btrfs/@data /.btrfs/@snapshots/@data/hourly --total 8
0 * * * * 	root 	 /usr/local/bin/btrfs-backup /.btrfs/@log /.btrfs/@snapshots/@log/hourly --total 8

Example for Anacrontab (/etc/anacrontab):
@daily   	 10 	 snapshot.daily.@      	 /usr/local/bin/btrfs-backup /.btrfs/@ /.btrfs/@snapshots/@/daily --total 8
@daily   	 10 	 snapshot.daily.@home  	 /usr/local/bin/btrfs-backup /.btrfs/@home /.btrfs/@snapshots/@home/daily --total 8
@daily   	 10 	 snapshot.daily.@data  	 /usr/local/bin/btrfs-backup /.btrfs/@data /.btrfs/@snapshots/@data/daily --total 8
@daily   	 10 	 snapshot.daily.@log   	 /usr/local/bin/btrfs-backup /.btrfs/@log /.btrfs/@snapshots/@log/daily --total 8

@weekly  	 20 	 snapshot.weekly.@     	 /usr/local/bin/btrfs-backup /.btrfs/@ /.btrfs/@snapshots/@/weekly --total 5
@weekly  	 20 	 snapshot.weekly.@home 	 /usr/local/bin/btrfs-backup /.btrfs/@home /.btrfs/@snapshots/@home/weekly --total 5
@weekly  	 20 	 snapshot.weekly.@data 	 /usr/local/bin/btrfs-backup /.btrfs/@data /.btrfs/@snapshots/@data/weekly --total 5
@weekly  	 20 	 snapshot.weekly.@log  	 /usr/local/bin/btrfs-backup /.btrfs/@log /.btrfs/@snapshots/@log/weekly --total 5

@monthly 	 30 	 snapshot.monthly.@     	/usr/local/bin/btrfs-backup /.btrfs/@ /.btrfs/@snapshots/@/monthly --total 3
@monthly 	 30 	 snapshot.monthly.@home 	/usr/local/bin/btrfs-backup /.btrfs/@home /.btrfs/@snapshots/@home/monthly --total 3
@monthly 	 30 	 snapshot.monthly.@data 	/usr/local/bin/btrfs-backup /.btrfs/@data /.btrfs/@snapshots/@data/monthly --total 3
@monthly 	 30 	 snapshot.monthly.@log  	/usr/local/bin/btrfs-backup /.btrfs/@log /.btrfs/@snapshots/@log/monthly --total 3
EOF
}

backup() {
  local now="$(date '+%Y_%M_%dT%H_%M_%S')"
  local name="$now"
  if [[ "$SNAPSHOT_NAME" ]]; then
    name="$name-$SNAPSHOT_NAME"
  fi
  btrfs subvolume snapshot -r "$SUBVOLUME" "$BACKUP_DIR/$name"

  # Clean up older snapshots
  if [[ "$TOTAL_BACKUPS" -ne 0 ]]; then
    for i in $(find "$BACKUP_DIR" -maxdepth 1 | sort | head -n -"${TOTAL_BACKUPS}"); do
      btrfs subvolume delete "$i"
    done
  fi
}

# Extract the last two arguments
SUBVOLUME="$1"
BACKUP_DIR="$2"
shift
shift

if [[ -z "$SUBVOLUME" || -z "$BACKUP_DIR" ]]; then
  echo "Error: Both subvolume and backup_dir must be provided."
  usage
  exit 1
fi

if [[ ! -d "$SUBVOLUME" ]]; then
  echo "Error: Specified subvolume path isn't a valid directory."
  exit 1
fi

if [[ ! -d "$BACKUP_DIR" ]]; then
  echo "Error: Specified backup directory path isn't a valid directory."
  exit 1
fi

TOTAL_BACKUPS=0
SNAPSHOT_NAME=""

while [[ "$1" ]]; do
  case "$1" in
  -h | --help)
    usage
    exit 0
    ;;
  -t | --total)
    shift
    TOTAL_BACKUPS="$1"
    shift
    ;;
  -n | --name)
    shift
    SNAPSHOT_NAME="$1"
    shift
    ;;
  *)
    echo "Error: Unknown argument: $1"
    usage
    exit 1
    ;;
  esac
done

backup