set -o pipefail

retention_days="30"
scan_roots=(
  /
  /home
  /root
  /srv
  /opt
  /tmp
  /var/tmp
  /var/lib
)

root_seen() {
  local candidate="$1"
  local seen

  for seen in "${seen_roots[@]}"; do
    [ "$candidate" = "$seen" ] && return 0
  done

  return 1
}

has_recent_activity() {
  local path="$1"

  find "$path" \
    -xdev \
    \( -name .git -o -name .hg -o -name .svn -o -name node_modules -o -name target \) -prune \
    -o -mindepth 1 -mtime "-$retention_days" -print -quit 2>/dev/null \
    | grep -q .
}

is_nix_store_symlink() {
  local link="$1"
  local target

  target="$(readlink "$link" 2>/dev/null || true)"
  case "$target" in
    /nix/store/*) return 0 ;;
    *) return 1 ;;
  esac
}

cleanup_direnv() {
  local direnv_dir="$1"
  local project_dir

  project_dir="$(dirname "$direnv_dir")"

  if [ ! -e "$project_dir/flake.nix" ] \
    && [ ! -e "$direnv_dir/flake-profile" ] \
    && [ ! -e "$direnv_dir/gcroots" ]; then
    return
  fi

  if has_recent_activity "$project_dir"; then
    return
  fi

  echo "Removing stale nix-direnv cache: $direnv_dir"
  rm -rf --one-file-system "$direnv_dir"
}

cleanup_result_link() {
  local link="$1"

  if ! is_nix_store_symlink "$link"; then
    return
  fi

  echo "Removing stale Nix build result symlink: $link"
  rm -f "$link"
}

seen_roots=()

for root in "${scan_roots[@]}"; do
  [ -d "$root" ] || continue
  root="$(readlink -f "$root")"
  root_seen "$root" && continue
  seen_roots+=("$root")

  find "$root" \
    -xdev \
    \( -path /nix -o -path /proc -o -path /sys -o -path /dev -o -path /run -o -path /boot \) -prune \
    -o -type d -name .direnv -mtime "+$retention_days" -print0 2>/dev/null \
    | while IFS= read -r -d "" direnv_dir; do
      cleanup_direnv "$direnv_dir"
    done

  find "$root" \
    -xdev \
    \( -path /nix -o -path /proc -o -path /sys -o -path /dev -o -path /run -o -path /boot \) -prune \
    -o -type l \( -name result -o -name "result-*" \) -mtime "+$retention_days" -print0 2>/dev/null \
    | while IFS= read -r -d "" link; do
      cleanup_result_link "$link"
    done
done