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

with lib;

let

  cfg = config.services.hydra;

  baseDir = "/var/lib/hydra";

  hydraConf = pkgs.writeScript "hydra.conf" cfg.extraConfig;

  hydraEnv =
    { HYDRA_DBI = cfg.dbi;
      HYDRA_CONFIG = "${baseDir}/hydra.conf";
      HYDRA_DATA = "${baseDir}";
    };

  env =
    { NIX_REMOTE = "daemon";
      SSL_CERT_FILE = "/etc/ssl/certs/ca-certificates.crt"; # Remove in 16.03
      PGPASSFILE = "${baseDir}/pgpass";
    } // hydraEnv // cfg.extraEnv;

  serverEnv = env //
    { HYDRA_TRACKER = cfg.tracker;
      COLUMNS = "80";
      PGPASSFILE = "${baseDir}/pgpass-www"; # grrr
    } // (optionalAttrs cfg.debugServer { DBIC_TRACE = 1; });

  localDB = "dbi:Pg:dbname=hydra;user=hydra;";

  haveLocalDB = cfg.dbi == localDB;

in

{
  ###### interface
  options = {

    services.hydra = rec {

      enable = mkOption {
        type = types.bool;
        default = false;
        description = ''
          Whether to run Hydra services.
        '';
      };

      dbi = mkOption {
        type = types.str;
        default = localDB;
        example = "dbi:Pg:dbname=hydra;host=postgres.example.org;user=foo;";
        description = ''
          The DBI string for Hydra database connection.
        '';
      };

      package = mkOption {
        type = types.path;
        #default = pkgs.hydra;
        description = "The Hydra package.";
      };

      hydraURL = mkOption {
        type = types.str;
        description = ''
          The base URL for the Hydra webserver instance. Used for links in emails.
        '';
      };

      listenHost = mkOption {
        type = types.str;
        default = "*";
        example = "localhost";
        description = ''
          The hostname or address to listen on or <literal>*</literal> to listen
          on all interfaces.
        '';
      };

      port = mkOption {
        type = types.int;
        default = 3000;
        description = ''
          TCP port the web server should listen to.
        '';
      };

      minimumDiskFree = mkOption {
        type = types.int;
        default = 0;
        description = ''
          Threshold of minimum disk space (GiB) to determine if the queue runner should run or not.
        '';
      };

      minimumDiskFreeEvaluator = mkOption {
        type = types.int;
        default = 0;
        description = ''
          Threshold of minimum disk space (GiB) to determine if the evaluator should run or not.
        '';
      };

      notificationSender = mkOption {
        type = types.str;
        description = ''
          Sender email address used for email notifications.
        '';
      };

      tracker = mkOption {
        type = types.str;
        default = "";
        description = ''
          Piece of HTML that is included on all pages.
        '';
      };

      logo = mkOption {
        type = types.nullOr types.path;
        default = null;
        description = ''
          Path to a file containing the logo of your Hydra instance.
        '';
      };

      debugServer = mkOption {
        type = types.bool;
        default = false;
        description = "Whether to run the server in debug mode.";
      };

      extraConfig = mkOption {
        type = types.lines;
        description = "Extra lines for the Hydra configuration.";
      };

      extraEnv = mkOption {
        type = types.attrsOf types.str;
        default = {};
        description = "Extra environment variables for Hydra.";
      };

      gcRootsDir = mkOption {
        type = types.path;
        default = "/nix/var/nix/gcroots/hydra";
        description = "Directory that holds Hydra garbage collector roots.";
      };
    };

  };


  ###### implementation

  config = mkIf cfg.enable {

    users.extraGroups.hydra = { };

    users.extraUsers.hydra =
      { description = "Hydra";
        group = "hydra";
        createHome = true;
        home = baseDir;
        useDefaultShell = true;
      };

    users.extraUsers.hydra-queue-runner =
      { description = "Hydra queue runner";
        group = "hydra";
        useDefaultShell = true;
        home = "${baseDir}/queue-runner"; # really only to keep SSH happy
      };

    users.extraUsers.hydra-www =
      { description = "Hydra web server";
        group = "hydra";
        useDefaultShell = true;
      };

    nix.trustedUsers = [ "hydra-queue-runner" ];

    services.hydra.package = mkDefault ((import ./release.nix {}).build.x86_64-linux);

    services.hydra.extraConfig =
      ''
        using_frontend_proxy 1
        base_uri ${cfg.hydraURL}
        notification_sender ${cfg.notificationSender}
        max_servers 25
        ${optionalString (cfg.logo != null) ''
          hydra_logo ${cfg.logo}
        ''}
        gc_roots_dir ${cfg.gcRootsDir}
      '';

    environment.systemPackages = [ cfg.package ];

    environment.variables = hydraEnv;

    nix.extraOptions = ''
      gc-keep-outputs = true
      gc-keep-derivations = true

      # The default (`true') slows Nix down a lot since the build farm
      # has so many GC roots.
      gc-check-reachability = false
    '';

    systemd.services.hydra-init =
      { wantedBy = [ "multi-user.target" ];
        requires = optional haveLocalDB "postgresql.service";
        after = optional haveLocalDB "postgresql.service";
        environment = env;
        preStart = ''
          mkdir -p ${baseDir}
          chown hydra.hydra ${baseDir}
          chmod 0750 ${baseDir}

          ln -sf ${hydraConf} ${baseDir}/hydra.conf

          mkdir -m 0700 -p ${baseDir}/www
          chown hydra-www.hydra ${baseDir}/www

          mkdir -m 0700 -p ${baseDir}/queue-runner
          mkdir -m 0750 -p ${baseDir}/build-logs
          chown hydra-queue-runner.hydra ${baseDir}/queue-runner ${baseDir}/build-logs

          ${optionalString haveLocalDB ''
            if ! [ -e ${baseDir}/.db-created ]; then
              ${config.services.postgresql.package}/bin/createuser hydra
              ${config.services.postgresql.package}/bin/createdb -O hydra hydra
              touch ${baseDir}/.db-created
            fi
          ''}

          if [ ! -e ${cfg.gcRootsDir} ]; then

            # Move legacy roots directory.
            if [ -e /nix/var/nix/gcroots/per-user/hydra/hydra-roots ]; then
              mv /nix/var/nix/gcroots/per-user/hydra/hydra-roots ${cfg.gcRootsDir}
            fi

            mkdir -p ${cfg.gcRootsDir}
          fi

          # Move legacy hydra-www roots.
          if [ -e /nix/var/nix/gcroots/per-user/hydra-www/hydra-roots ]; then
            find /nix/var/nix/gcroots/per-user/hydra-www/hydra-roots/ -type f \
              | xargs -r mv -f -t ${cfg.gcRootsDir}/
            rmdir /nix/var/nix/gcroots/per-user/hydra-www/hydra-roots
          fi

          chown hydra.hydra ${cfg.gcRootsDir}
          chmod 2775 ${cfg.gcRootsDir}
        '';
        serviceConfig.ExecStart = "${cfg.package}/bin/hydra-init";
        serviceConfig.PermissionsStartOnly = true;
        serviceConfig.User = "hydra";
        serviceConfig.Type = "oneshot";
        serviceConfig.RemainAfterExit = true;
      };

    systemd.services.hydra-server =
      { wantedBy = [ "multi-user.target" ];
        requires = [ "hydra-init.service" ];
        after = [ "hydra-init.service" ];
        environment = serverEnv;
        serviceConfig =
          { ExecStart =
              "@${cfg.package}/bin/hydra-server hydra-server -f -h '${cfg.listenHost}' "
              + "-p ${toString cfg.port} --max_spare_servers 5 --max_servers 25 "
              + "--max_requests 100 ${optionalString cfg.debugServer "-d"}";
            User = "hydra-www";
            PermissionsStartOnly = true;
            Restart = "always";
          };
      };

    systemd.services.hydra-queue-runner =
      { wantedBy = [ "multi-user.target" ];
        requires = [ "hydra-init.service" ];
        after = [ "hydra-init.service" "network.target" ];
        path = [ cfg.package pkgs.nettools pkgs.ssmtp pkgs.openssh pkgs.bzip2 ];
        environment = env // {
          PGPASSFILE = "${baseDir}/pgpass-queue-runner"; # grrr
          IN_SYSTEMD = "1"; # to get log severity levels
        };
        serviceConfig =
          { ExecStart = "@${cfg.package}/bin/hydra-queue-runner hydra-queue-runner -v --option build-use-substitutes false";
            ExecStopPost = "${cfg.package}/bin/hydra-queue-runner --unlock";
            User = "hydra-queue-runner";
            Restart = "always";

            # Ensure we can get core dumps.
            LimitCORE = "infinity";
            WorkingDirectory = "${baseDir}/queue-runner";
          };
      };

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

    systemd.services.hydra-update-gc-roots =
      { requires = [ "hydra-init.service" ];
        after = [ "hydra-init.service" ];
        environment = env;
        serviceConfig =
          { ExecStart = "@${cfg.package}/bin/hydra-update-gc-roots hydra-update-gc-roots";
            User = "hydra";
          };
        startAt = "2,14:15";
      };

    systemd.services.hydra-send-stats =
      { wantedBy = [ "multi-user.target" ];
        after = [ "hydra-init.service" ];
        environment = env;
        serviceConfig =
          { ExecStart = "@${cfg.package}/bin/hydra-send-stats hydra-send-stats";
            User = "hydra";
          };
      };

    # If there is less than a certain amount of free disk space, stop
    # the queue/evaluator to prevent builds from failing or aborting.
    systemd.services.hydra-check-space =
      { script =
          ''
            if [ $(($(stat -f -c '%a' /nix/store) * $(stat -f -c '%S' /nix/store))) -lt $((${toString cfg.minimumDiskFree} * 1024**3)) ]; then
                echo "stopping Hydra queue runner due to lack of free space..."
                systemctl stop hydra-queue-runner
            fi
            if [ $(($(stat -f -c '%a' /nix/store) * $(stat -f -c '%S' /nix/store))) -lt $((${toString cfg.minimumDiskFreeEvaluator} * 1024**3)) ]; then
                echo "stopping Hydra evaluator due to lack of free space..."
                systemctl stop hydra-evaluator
            fi
          '';
        startAt = "*:0/5";
      };

    # Periodically compress build logs. The queue runner compresses
    # logs automatically after a step finishes, but this doesn't work
    # if the queue runner is stopped prematurely.
    systemd.services.hydra-compress-logs =
      { path = [ pkgs.bzip2 ];
        script =
          ''
            find /var/lib/hydra/build-logs -type f -name "*.drv" -mtime +3 -size +0c | xargs -r bzip2 -v -f
          '';
        startAt = "Sun 01:45";
      };

    services.postgresql.enable = mkIf haveLocalDB true;

    services.postgresql.identMap = optionalString haveLocalDB
      ''
        hydra-users hydra hydra
        hydra-users hydra-queue-runner hydra
        hydra-users hydra-www hydra
        hydra-users root hydra
      '';

    services.postgresql.authentication = optionalString haveLocalDB
      ''
        local hydra all ident map=hydra-users
      '';

  };

}