{ config, lib, pkgs, ... }:

with lib;

let
  cfg = config.systemd.status-mail;

  systemdCfg = foldr singleCfg {} cfg.onFailure;
  singleCfg = unitName: attrs: attrs // (setAttrByPath ["systemd" "services" unitName "onFailure"] ["unit-status-mail@%n.service"]);
in {
  options = {
    systemd.status-mail = {
      onFailure = mkOption {
        default = [];
        type = types.listOf types.str;
        description = ''
          Send status mail when these units fail
        '';
      };

      recipient = mkOption {
        default = "root";
        type = types.str;
        description = ''
          Recipient of status mails
        '';
      };
    };
  };

  config = mkIf (cfg.onFailure != []) {
    systemd.services."unit-status-mail@" = {
      serviceConfig = {
        Type = "oneshot";
      };
      scriptArgs = "%I \"Hostname: %H\" \"Machine-ID: %m\" \"Boot-ID: %b\"";
      script = ''
        #!${pkgs.stdenv.shell}
        MAILTO="${cfg.recipient}"
        MAILFROM="unit-status-mailer"
        UNIT=$1

        EXTRA=""
        for e in "''${@:2}"; do
          EXTRA+="$e"$'\n'
        done

        UNITSTATUS=$(systemctl status $UNIT)

        ${config.security.wrapperDir}/sendmail $MAILTO <<EOF
        From:$MAILFROM
        To:$MAILTO
        Subject:Status of $UNIT

        Status report for unit: $UNIT
        $EXTRA

        $UNITSTATUS
        EOF
      '';
    };
  };
}