# Suspend:
#   sudo systemctl suspend
# Suspend for 60 seconds:
#   sudo rtcwake -m mem -s 60

# Power consumption:
#    2.4W powered off, with 1 RAM, 1 SSD
#    2.6W suspended, with 1 RAM, 1 SSD
#    2.6W suspended, with 1 RAM, 1 SSD, 2 HDDs
#   18.9W idle, with 1 RAM, 1 SSD, 2 HDDs

# View service log:
#   journalctl -u daily-backup-and-suspend

# Print unit file:
#   cat "$(systemctl show -P FragmentPath daily-backup-and-suspend.service)"

{ config, pkgs, ... }:
let
  backup-source = "rootNas";
  # The "stay-awake" file is located at `${backup-source}:${stay-awake-file}`.
  stay-awake-file = "${config.networking.hostName}.stay-awake";
in
{
  yoda.de-p1st-monitor = (builtins.readFile ../../assets/de-p1st-monitor/yodaHedgehog.ini);

  assertions = [{
    assertion = config.services.openssh.enable;
    message = "systemd service daily-backup-and-suspend requires SSH.";
  } {
    assertion = config.services.journalwatch.enable;
    message = "systemd service daily-backup-and-suspend requires journalwatch.";
  }];

  systemd.timers."daily-backup-and-suspend" = {
    wantedBy = [ "multi-user.target" ];
    timerConfig = {
      OnCalendar = [
        # Daily
        "*-*-* 00:00:05"
      ];
      WakeSystem = true;
    };
  };
  systemd.services."daily-backup-and-suspend" = {
    # Packages required for this script.
    # For `ssh` and `journalwatch`, there are assertions above.
    path = with pkgs; [
      # Provides `ssh`
      openssh
      # Provides `awk`, `grep`, `sleep`, `printf`, `echo`, 'sendmail'
      busybox
      # Provides `smtpctl`
      opensmtpd
    ];
    # Script to execute as main process.
    script = ''
      set -eu -o pipefail
      printf '%s\n' 'Starting backup script.'

      # TODO: Backup: Pull BTRFS snapshots from ${backup-source}.

      # Don't suspend as long as `${backup-source}:${stay-awake-file}` exists.
      while :; do
        result="$(ssh ${backup-source} 'ls ${stay-awake-file} 2>&1')" ||:
        case "''${result}" in
          *"No such file or directory")
            break
            ;;
          "${stay-awake-file}")
            printf '%s\n' 'Delaying suspend due to ${stay-awake-file} file.'
            ;;
          *)
            printf '%s\n' 'Delaying suspend due to SSH connectivity problems.'
            ;;
        esac
        sleep 10s
      done

      # Wait until no BTRFS scrub service is running.
      while :; do
        running_services="$(systemctl list-units --type=service --plain --quiet | awk '{ print $1 }')"
        if ! printf '%s' "''${running_services}" | grep '^btrfs-scrub'; then
          break;
        fi
        printf '%s\n' 'Delaying suspend due to running BTRFS scrub service.'
        sleep 60s
      done

      # Send filtered journal by email.
      systemctl start journalwatch.service ||:
      # Send notification by email.
      printf '%s\n\n%s' 'Subject: ${config.networking.hostName}' 'Finished backup.' | sendmail -f langbein@mail.de daniel@systemli.org

      # Let sendmail send emails.
      #while :; do
      #  # TODO: Plain usage of `smtpctl` gives the error:
      #  #   smtpctl: this program must be setgid smtpq
      #  queue="$(smtpctl show queue)"
      #  if [ "''${queue}" = "" ]; then
      #    break
      #  fi
      #  printf '%s\n' 'Delaying suspend due to non-empty smtpd email queue.'
      #  sleep 1s
      #done
      sleep 15s

      printf '%s\n' 'Finished backup script.'
      # Suspend to save power.
      systemctl suspend
    '';
  };
}