#!/usr/bin/env bash
# ─────────────────────────────────────────────────────────────────────────────
# arcline-snapshot — btrfs snapshot manager (ships at /usr/local/sbin)
#
#   arcline-snapshot snapshot            take a snapshot of @ and @home
#   arcline-snapshot list                list stored snapshots
#   arcline-snapshot prune [--keep N]    keep N newest, delete the rest
#
# Snapshots are read-only copies under /.snapshots, so they survive a failed
# upgrade. Run as root (or via sudo). Configured through the
# arcline-snapshot.timer unit (see overlays/base/usr/lib/systemd/system/).
# ─────────────────────────────────────────────────────────────────────────────
set -euo pipefail

ACTION="${1:-list}"
SNAP_ROOT="/.snapshots"
KEEP="${ARCLINE_SNAPSHOT_KEEP:-5}"
TOP="/run/arcline-btrfs"

require_root() {
  if [[ $EUID -ne 0 ]] && command -v sudo >/dev/null; then
    exec sudo -E "$0" "$@"
  elif [[ $EUID -ne 0 ]]; then
    echo "error: needs root" >&2; exit 1
  fi
}

ROOT_FS_TYPE="$(findmnt -no FSTYPE / 2>/dev/null || true)"
if [[ "$ROOT_FS_TYPE" != "btrfs" ]]; then
  echo "info: root filesystem is '$ROOT_FS_TYPE', not btrfs — snapshots disabled"
  exit 0
fi
ROOT_DEV="$(findmnt -no SOURCE / | head -1)"

mount_top() {
  mkdir -p "$TOP"
  mount -o subvolid=5,ro "$ROOT_DEV" "$TOP"
  trap 'umount "$TOP" 2>/dev/null || true; rmdir "$TOP" 2>/dev/null || true' EXIT
}

stamp() { date +%Y%m%dT%H%M%S; }

case "$ACTION" in
  snapshot)
    require_root "$0" "$@"
    mount_top
    ts="$(stamp)"
    for sub in "@" "@home"; do
      [[ -d "$TOP/$sub" ]] || { echo "warn: subvolume $sub not found, skipping"; continue; }
      dst="$TOP/@snapshots/$ts-$sub"
      echo "snapshotting $sub → $dst"
      btrfs subvolume snapshot -r "$TOP/$sub" "$dst" >/dev/null
    done
    echo "snapshot taken: $ts"
    ;;

  list)
    require_root "$0" "$@"
    mount_top
    if ! compgen -G "$TOP/@snapshots/*-@*" >/dev/null; then
      echo "no snapshots yet"
      exit 0
    fi
    for snap in "$TOP"/@snapshots/*-@*; do
      [[ -d "$snap" ]] || continue
      echo "$(basename "$snap")"
    done | sort -r
    ;;

  prune)
    require_root "$0" "$@"
    mount_top
    if [[ "${2:-}" == "--keep" ]]; then KEEP="${3:-$KEEP}"; fi
    mapfile -t snaps < <(for s in "$TOP"/@snapshots/*-@*; do [[ -d "$s" ]] && echo "$s"; done | sort -r)
    if [[ ${#snaps[@]} -le $KEEP ]]; then
      echo "nothing to prune (${#snaps[@]} ≤ keep $KEEP)"
      exit 0
    fi
    for old in "${snaps[@]:$KEEP}"; do
      echo "deleting $(basename "$old")"
      btrfs subvolume delete "$old" >/dev/null
    done
    ;;

  *)
    echo "usage: arcline-snapshot {snapshot|list|prune [--keep N]}" >&2
    exit 1
    ;;
esac