env = ''export NIX_REMOTE=daemon ''
      + ''HYDRA_DBI="${cfg.dbi}" ''
      + ''HYDRA_CONFIG=${cfg.baseDir}/data/hydra.conf ''
      + ''HYDRA_DATA=${cfg.baseDir}/data ''
      + ''HYDRA_PORT="${toString cfg.port}" ''
      + (if cfg.logo != null
         then ''HYDRA_LOGO="${cfg.logo}" ''
         else "")
      + ''HYDRA_TRACKER="${cfg.tracker}" ;'';

  env =
    { NIX_REMOTE = "daemon";
      HYDRA_DBI = cfg.dbi;
      HYDRA_CONFIG = "${cfg.baseDir}/data/hydra.conf";
      HYDRA_DATA = "${cfg.baseDir}/data";
      HYDRA_PORT = "${toString cfg.port}";
      OPENSSL_X509_CERT_FILE = "/etc/ssl/certs/ca-bundle.crt";
    };
  
  serverEnv = env //
    { HYDRA_LOGO = if cfg.logo != null then cfg.logo else "";
      HYDRA_TRACKER = cfg.tracker;
    };

        default = pkgs.hydra;

        #default = pkgs.hydra;

      
      useWAL = mkOption {
        default = true;
        description = ''
          Whether to use SQLite's Write-Ahead Logging, which may improve performance.
        '';
      };

      
      # Online log compression makes it impossible to get the tail of
      # builds that are in progress.
      build-compress-log = false

      use-sqlite-wal = false

      use-sqlite-wal = ${if cfg.useWAL then "true" else "false"}

    jobs.hydra_init =
      { description = "hydra-init";
        startOn = "started network-interfaces";
        preStart = ''

    jobs."hydra-init" =
      { wantedBy = [ "multi-user.target" ];
        script = ''

        exec = ''
          echo done
        '';

        task = true;
      };
    
    systemd.services."hydra-server" =
      { wantedBy = [ "multi-user.target" ];
        wants = [ "hydra-init.service" ];
        after = [ "hydra-init.service" ];
        environment = serverEnv;
        serviceConfig =
          { ExecStart = "@${cfg.hydra}/bin/hydra-server hydra-server -f -h \* --max_spare_servers 5 --max_servers 25 --max_requests 100";
            User = cfg.user;
            Restart = "always";
          };

    jobs.hydra_server =
      { description = "hydra-server";
        startOn = if cfg.autoStart then "started network-interfaces hydra-init" else "never";
        exec = ''
          ${pkgs.su}/bin/su - ${cfg.user} -c '${env} ${cfg.hydra}/bin/hydra-server > ${cfg.baseDir}/data/server.log 2>&1'
        '';

    systemd.services."hydra-queue-runner" =
      { wantedBy = [ "multi-user.target" ];
        wants = [ "hydra-init.service" ];
        after = [ "hydra-init.service" "network.target" ];
        path = [ pkgs.nettools pkgs.ssmtp ];
        environment = env;
        serviceConfig =
          { ExecStartPre = "${cfg.hydra}/bin/hydra-queue-runner --unlock";
            ExecStart = "@${cfg.hydra}/bin/hydra-queue-runner hydra-queue-runner";
            User = cfg.user;
            Restart = "always";
          };

    jobs.hydra_queue_runner =
      { description = "hydra-queue-runner";
        startOn = if cfg.autoStart then "started network-interfaces hydra-init" else "never";
        preStart = "${pkgs.su}/bin/su - ${cfg.user} -c '${env} ${cfg.hydra}/bin/hydra-queue-runner --unlock'";
        exec = ''
          ${pkgs.su}/bin/su - ${cfg.user} -c '${env} nice -n 8 ${cfg.hydra}/bin/hydra-queue-runner > ${cfg.baseDir}/data/queue-runner.log 2>&1'
        '';

    systemd.services."hydra-evaluator" =
      { wantedBy = [ "multi-user.target" ];
        wants = [ "hydra-init.service" ];
        after = [ "hydra-init.service" "network.target" ];
        path = [ pkgs.nettools pkgs.ssmtp ];
        environment = env;
        serviceConfig =
          { ExecStart = "@${cfg.hydra}/bin/hydra-evaluator hydra-evaluator";
            User = cfg.user;
            Restart = "always";
          };

    jobs.hydra_evaluator =
      { description = "hydra-evaluator";
        startOn = if cfg.autoStart then "started network-interfaces hydra-init" else "never";
        exec = ''
          ${pkgs.su}/bin/su - ${cfg.user} -c '${env} nice -n 5 ${cfg.hydra}/bin/hydra-evaluator > ${cfg.baseDir}/data/evaluator.log 2>&1'
        '';

    systemd.services."hydra-update-gc-roots" =
      { wants = [ "hydra-init.service" ];
        after = [ "hydra-init.service" ];
        environment = env;
        serviceConfig =
          { ExecStart = "@${cfg.hydra}/bin/hydra-update-gc-roots hydra-update-gc-roots";
            User = cfg.user;
          };

          stop hydra_queue_runner

                stop hydra_queue_runner

        if [ $(($(stat -f -c '%a' /nix/store) * $(stat -f -c '%S' /nix/store))) -lt $((${toString cfg.minimumDiskFreeEvaluator} * 1024**3)) ]; then
          stop hydra_evaluator
        fi
          '';
        collect = pkgs.writeScript "collect-some-garbage"
          # Arrange to always have at least 100 GiB free.
          '' #!/bin/sh -e
             available="$(df -B1 /nix/store | tail -n 1 | awk '{ print $4 }')"
             target="$((100 * 1024**3))"
             to_free="$(($available > $target ? 200 * 1024**2 : $target - $available))"
             echo "$available B available, and targeting $target B available"
             echo "thus, freeing $to_free B"
             exec "${pkgs.nix}/bin/nix-collect-garbage" --max-freed "$to_free"

            if [ $(($(stat -f -c '%a' /nix/store) * $(stat -f -c '%S' /nix/store))) -lt $((${toString cfg.minimumDiskFreeEvaluator} * 1024**3)) ]; then
                stop hydra_evaluator
            fi

        [ "15 03 * * * root  ${collect} &> ${cfg.baseDir}/data/gc.log"
          "15 13 * * * root  ${collect} &> ${cfg.baseDir}/data/gc.log"
          "*/5 * * * * root  ${checkSpace} &> ${cfg.baseDir}/data/checkspace.log"

        [ "*/5 * * * * root  ${checkSpace} &> ${cfg.baseDir}/data/checkspace.log"

          "15 02 * * * ${cfg.user} ${env} ${cfg.hydra}/bin/hydra-update-gc-roots &> ${cfg.baseDir}/data/gc-roots.log"

          "15 2 * * * root  ${pkgs.systemd}/bin/systemctl start hydra-update-gc-roots.service"