# NAS auto-shutdown
# Powers the machine off when all of the following are true:
#   1. No active SSH session
#   2. pyload is not downloading (no non-local TCP peers)
#   3. pyload has no hook children (extraction, filebot, unrar, ...)
#   4. Both spinning HDDs are in standby
#   5. At least 15 minutes have passed since boot (via OnBootSec)
# The fw host re-wakes the NAS on demand via WOL
# (see hosts/fw/modules/nas-wake-on-access.nix).
{ config, lib, pkgs, ... }:

let
  # Spinning disks whose power state gates the shutdown decision.
  # Only the Toshiba HDDs; NVMe drives do not spin down.
  hdds = [
    "/dev/disk/by-id/ata-TOSHIBA_MG10ACA20TE_8582A01SF4MJ"
    "/dev/disk/by-id/ata-TOSHIBA_MG10ACA20TE_75V2A0H3F4MJ"
  ];

  # Peer addresses that do not count as "real download traffic":
  # loopback, internal VLAN (10.42.0.0/16), and IPv6 loopback / link-local.
  localPeerRegex = "^(127\\.|10\\.42\\.|\\[::1\\]|\\[fe80)";

  autoShutdownScript = pkgs.writeShellScript "nas-auto-shutdown" ''
    set -euo pipefail
    log() { echo "auto-shutdown: $*"; }

    # 1. SSH sessions. Cheapest check and it prevents shutting down while an
    # admin is logged in. Uses ss at the socket layer so it catches
    # forwarding-only sessions and `ssh host 'cmd'` runs that utmp misses.
    # NOTE: SSH port hardcoded to 22 — keep in sync with configuration.nix.
    ssh_sessions=$(${pkgs.iproute2}/bin/ss -H -t -n state established '( sport = :22 )' || true)
    if [[ -n "$ssh_sessions" ]]; then
      log "active SSH session present, staying up"
      exit 0
    fi

    # 2. pyload active downloads: any established/outgoing pyload-owned socket
    # to a non-local peer means a download is in flight.
    pyload_conns=$(${pkgs.iproute2}/bin/ss -H -t -n -p \
        state established state syn-sent state syn-recv 2>/dev/null \
      | grep -F 'pyload' \
      | awk '{print $5}' \
      | grep -Ev '${localPeerRegex}' || true)
    if [[ -n "$pyload_conns" ]]; then
      log "pyload has active non-local connections, staying up"
      exit 0
    fi

    # 3. pyload hook children (extraction, filebot, unrar, 7z, java, ...).
    # The package_finished hook is launched by pyload's ExternalScripts
    # plugin, so every child lives in pyload.service's cgroup. cgroup.procs
    # contains PIDs/TGIDs only, not TIDs, so pyload's internal thread pool
    # cannot false-positive. Fail-safe: if the file is unreadable, stay up.
    cgroup_procs=/sys/fs/cgroup/system.slice/pyload.service/cgroup.procs
    if [[ ! -r "$cgroup_procs" ]]; then
      log "pyload cgroup procs file unreadable ($cgroup_procs), staying up"
      exit 0
    fi
    main_pid=$(${pkgs.systemd}/bin/systemctl show -p MainPID --value pyload.service)
    children=$(grep -v -x -F "$main_pid" "$cgroup_procs" || true)
    if [[ -n "$children" ]]; then
      log "pyload hook children running ($(echo "$children" | tr '\n' ' ')), staying up"
      exit 0
    fi

    # 4. Both spinning HDDs must be in standby. hdparm -C is non-disturbing
    # (does not wake the disk). The udev rule in power-management.nix runs
    # hdparm -S 180, so standby implies >= 15 min of firmware-level idle —
    # no extra shell-level debounce needed.
    for disk in ${lib.concatStringsSep " " hdds}; do
      if [[ ! -e "$disk" ]]; then
        log "disk $disk missing, staying up"
        exit 0
      fi
      device=$(readlink -f "$disk")
      power_state=$(${pkgs.hdparm}/bin/hdparm -C "$device" 2>/dev/null \
        | grep -oP '(standby|active/idle|active|idle)' | head -1 || echo "unknown")
      if [[ "$power_state" != "standby" ]]; then
        log "$disk is $power_state, staying up"
        exit 0
      fi
    done

    # 5. All clear.
    log "all checks clear, powering off"
    ${pkgs.systemd}/bin/systemctl poweroff
  '';
in
{
  systemd.services.nas-auto-shutdown = {
    description = "Power off NAS when idle (HDD standby + pyload/filebot quiet + no SSH)";
    path = with pkgs; [ coreutils gawk gnugrep iproute2 hdparm systemd ];
    serviceConfig = {
      Type = "oneshot";
      User = "root";
      ExecStart = "${autoShutdownScript}";
    };
  };

  systemd.timers.nas-auto-shutdown = {
    description = "Run NAS idle check every minute";
    wantedBy = [ "timers.target" ];
    timerConfig = {
      # Requirement: earliest shutdown is 15 min after boot, so a
      # WOL-triggered wake is not immediately followed by another poweroff.
      OnBootSec = "15min";
      OnUnitActiveSec = "1min";
      AccuracySec = "10s";
      Persistent = false;
    };
  };
}