srv:
{ configIniOfService
, srvsrht ? "${srv}srht" # Because "buildsrht" does not follow that pattern (missing an "s").
, iniKey ? "${srv}.sr.ht"
, webhooks ? false
, extraTimers ? {}
, mainService ? {}
, extraServices ? {}
, extraConfig ? {}
, port
}:
{ config, lib, pkgs, ... }:

with lib;
let
  inherit (config.services) postgresql redis;
  inherit (config.users) users;
  cfg = config.services.sourcehut;
  configIni = configIniOfService srv;
  srvCfg = cfg.${srv};
  baseService = serviceName: { allowStripe ? false }: extraService: let
    runDir = "/run/sourcehut/${serviceName}";
    rootDir = "/run/sourcehut/chroots/${serviceName}";
    in
    mkMerge [ extraService {
    after = [ "network.target" ]
      ++ optional cfg.postgresql.enable "postgresql.service"
      ++ optional cfg.redis.enable "redis.service";
    requires =
         optional cfg.postgresql.enable "postgresql.service"
      ++ optional cfg.redis.enable "redis.service";
    path = [ pkgs.gawk ];
    environment.HOME = runDir;
    serviceConfig = {
      User = mkDefault srvCfg.user;
      Group = mkDefault srvCfg.group;
      RuntimeDirectory = [
        "sourcehut/${serviceName}"
        "sourcehut/chroots/${serviceName}"
      ];
      RuntimeDirectoryMode = "2750";
      # No need for the chroot path once inside the chroot
      InaccessiblePaths = [ "-+${rootDir}" ];
      # g+rx is for group members (eg. fcgiwrap or nginx)
      # to read Git/Mercurial repositories, buildlogs, etc.
      # o+x is for intermediate directories created by BindPaths= and like,
      # as they're owned by root:root.
      UMask = "0026";
      RootDirectory = rootDir;
      RootDirectoryStartOnly = true;
      PrivateTmp = true;
      MountAPIVFS = true;
      # config.ini is looked up in there, before /etc/srht/config.ini
      # Note that it fails to be set in ExecStartPre=
      WorkingDirectory = mkDefault ("-"+runDir);
      BindReadOnlyPaths = [
        builtins.storeDir
        "/etc"
        "/run/booted-system"
        "/run/current-system"
        "/run/systemd"
        ] ++
        optional cfg.postgresql.enable "/run/postgresql" ++
        optional cfg.redis.enable "/run/redis";
      # LoadCredential= are unfortunately not available in ExecStartPre=
      # Hence this one is run as root (the +) with RootDirectoryStartOnly=
      # to reach credentials wherever they are.
      # Note that each systemd service gets its own ${runDir}/config.ini file.
      ExecStartPre = mkBefore [("+"+pkgs.writeShellScript "${serviceName}-credentials" ''
        set -x
        # Replace values begining with a '<' by the content of the file whose name is after.
        gawk '{ if (match($0,/^([^=]+=)<(.+)/,m)) { getline f < m[2]; print m[1] f } else print $0 }' ${configIni} |
        ${optionalString (!allowStripe) "gawk '!/^stripe-secret-key=/' |"}
        install -o ${srvCfg.user} -g root -m 400 /dev/stdin ${runDir}/config.ini
      '')];
      # The following options are only for optimizing:
      # systemd-analyze security
      AmbientCapabilities = "";
      CapabilityBoundingSet = "";
      # ProtectClock= adds DeviceAllow=char-rtc r
      DeviceAllow = "";
      LockPersonality = true;
      MemoryDenyWriteExecute = true;
      NoNewPrivileges = true;
      PrivateDevices = true;
      PrivateMounts = true;
      PrivateNetwork = mkDefault false;
      PrivateUsers = true;
      ProcSubset = "pid";
      ProtectClock = true;
      ProtectControlGroups = true;
      ProtectHome = true;
      ProtectHostname = true;
      ProtectKernelLogs = true;
      ProtectKernelModules = true;
      ProtectKernelTunables = true;
      ProtectProc = "invisible";
      ProtectSystem = "strict";
      RemoveIPC = true;
      RestrictAddressFamilies = [ "AF_UNIX" "AF_INET" "AF_INET6" ];
      RestrictNamespaces = true;
      RestrictRealtime = true;
      RestrictSUIDSGID = true;
      #SocketBindAllow = [ "tcp:${toString srvCfg.port}" "tcp:${toString srvCfg.prometheusPort}" ];
      #SocketBindDeny = "any";
      SystemCallFilter = [
        "@system-service"
        "~@aio" "~@keyring" "~@memlock" "~@privileged" "~@resources" "~@timer"
        "@chown" "@setuid"
      ];
      SystemCallArchitectures = "native";
    };
  } ];
in
{
  options.services.sourcehut.${srv} = {
    enable = mkEnableOption "${srv} service";

    user = mkOption {
      type = types.str;
      default = srvsrht;
      description = ''
        User for ${srv}.sr.ht.
      '';
    };

    group = mkOption {
      type = types.str;
      default = srvsrht;
      description = ''
        Group for ${srv}.sr.ht.
        Membership grants access to the Git/Mercurial repositories by default,
        but not to the config.ini file (where secrets are).
      '';
    };

    port = mkOption {
      type = types.port;
      default = port;
      description = ''
        Port on which the "${srv}" backend should listen.
      '';
    };

    postgresql = {
      database = mkOption {
        type = types.str;
        default = "${srv}.sr.ht";
        description = ''
          PostgreSQL database name for the ${srv}.sr.ht service,
          used if <xref linkend="opt-services.sourcehut.postgresql.enable"/> is <literal>true</literal>.
        '';
      };
    };
  };

  config = lib.mkIf (cfg.enable && srvCfg.enable) (mkMerge [ extraConfig {
    users = {
      users = {
        "${srvCfg.user}" = {
          isSystemUser = true;
          group = mkDefault srvCfg.group;
          description = mkDefault "sourcehut user for ${srv}.sr.ht";
        };
      };
      groups = {
        "${srvCfg.group}" = { };
      } // optionalAttrs (cfg.postgresql.enable
        && hasSuffix "0" (postgresql.settings.unix_socket_permissions or "")) {
        "postgres".members = [ srvCfg.user ];
      };
    };

    services.nginx = mkIf cfg.nginx.enable {
      virtualHosts."${srv}.${cfg.settings."sr.ht".global-domain}" = mkMerge [ {
        forceSSL = true;
        locations."/".proxyPass = "http://${cfg.listenAddress}:${toString srvCfg.port}";
        locations."/static" = {
          root = "${pkgs.sourcehut.${srvsrht}}/${pkgs.sourcehut.python.sitePackages}/${srvsrht}";
          extraConfig = mkDefault ''
            expires 30d;
          '';
        };
      } cfg.nginx.virtualHost ];
    };

    services.postgresql = mkIf cfg.postgresql.enable {
      authentication = ''
        local ${srvCfg.postgresql.database} ${srvCfg.user} trust
      ''
      # shrt-keys stores SSH keys in the PostgreSQL database of the service calling it
      + optionalString (elem srv ["builds" "git" "hg"]) ''
        local ${srvCfg.postgresql.database} ${users."sshsrht".name} trust
      '';
      ensureDatabases = [ srvCfg.postgresql.database ];
      ensureUsers = map (name: {
          inherit name;
          ensurePermissions = { "DATABASE \"${srvCfg.postgresql.database}\"" = "ALL PRIVILEGES"; };
        }) ([srvCfg.user] ++ optional (elem srv ["builds" "git" "hg"]) users."sshsrht".name);
    };

    services.sourcehut.services = mkDefault (filter (s: cfg.${s}.enable)
      [ "builds" "dispatch" "git" "hg" "hub" "lists" "man" "meta" "pages" "paste" "todo" ]);

    services.sourcehut.settings = mkMerge [
      {
        "${srv}.sr.ht" = {
          origin = mkDefault "https://${srv}.${cfg.settings."sr.ht".global-domain}";
        };
      }

      (mkIf cfg.postgresql.enable {
        "${srv}.sr.ht".connection-string = mkDefault "postgresql:///${srvCfg.postgresql.database}?user=${srvCfg.user}&host=/run/postgresql";
      })
    ];

    systemd.services = mkMerge [
      {
        "${srvsrht}" = baseService srvsrht { allowStripe = srv == "meta"; } (mkMerge [
        {
          description = "sourcehut ${srv}.sr.ht website service";
          before = optional cfg.nginx.enable "nginx.service";
          wants = optional cfg.nginx.enable "nginx.service";
          wantedBy = [ "multi-user.target" ];
          path = optional cfg.postgresql.enable postgresql.package;
          # Beware: change in credentials' content will not trigger restart.
          restartTriggers = [ configIni ];
          serviceConfig = {
            Type = "simple";
            Restart = mkDefault "always";
            #RestartSec = mkDefault "2min";
            StateDirectory = [ "sourcehut/${srvsrht}" ];
            StateDirectoryMode = "2750";
            ExecStart = "${cfg.python}/bin/gunicorn ${srvsrht}.app:app -b ${cfg.listenAddress}:${toString srvCfg.port}";
          };
          preStart = let
            version = pkgs.sourcehut.${srvsrht}.version;
            stateDir = "/var/lib/sourcehut/${srvsrht}";
            in mkBefore ''
            set -x
            # Use the /run/sourcehut/${srvsrht}/config.ini
            # installed by a previous ExecStartPre= in baseService
            cd /run/sourcehut/${srvsrht}

            if test ! -e ${stateDir}/db; then
              # Setup the initial database.
              # Note that it stamps the alembic head afterward
              ${cfg.python}/bin/${srvsrht}-initdb
              echo ${version} >${stateDir}/db
            fi

            ${optionalString cfg.settings.${iniKey}.migrate-on-upgrade ''
              if [ "$(cat ${stateDir}/db)" != "${version}" ]; then
                # Manage schema migrations using alembic
                ${cfg.python}/bin/${srvsrht}-migrate -a upgrade head
                echo ${version} >${stateDir}/db
              fi
            ''}

            # Update copy of each users' profile to the latest
            # See https://lists.sr.ht/~sircmpwn/sr.ht-admins/<20190302181207.GA13778%40cirno.my.domain>
            if test ! -e ${stateDir}/webhook; then
              # Update ${iniKey}'s users' profile copy to the latest
              ${cfg.python}/bin/srht-update-profiles ${iniKey}
              touch ${stateDir}/webhook
            fi
          '';
        } mainService ]);
      }

      (mkIf webhooks {
        "${srvsrht}-webhooks" = baseService "${srvsrht}-webhooks" {}
          {
            description = "sourcehut ${srv}.sr.ht webhooks service";
            before = [ "${srvsrht}.service" ];
            requiredBy = [ "${srvsrht}.service" ];
            serviceConfig = {
              Type = "simple";
              Restart = "always";
              # --queues enables sharing the Redis database amongst different celery workers
              ExecStart = "${cfg.python}/bin/celery -A ${srvsrht}.webhooks worker --queues sourcehut.${srvsrht}-webhooks --loglevel INFO --pool eventlet";
              # Avoid crashing: os.getloadavg()
              ProcSubset = mkForce "all";
              InaccessiblePaths = [ "-+/run/postgresql" ];
            };
          };
      })

      (mapAttrs (timerName: timer: (baseService timerName {} (mkMerge [
        {
          description = "sourcehut ${timerName} service";
          after = [ "network.target" "${srvsrht}.service" ];
          serviceConfig = {
            Type = "oneshot";
            ExecStart = "${cfg.python}/bin/${timerName}";
          };
        }
        (timer.service or {})
      ]))) extraTimers)

      (mapAttrs (serviceName: extraService: baseService serviceName {} (mkMerge [
        {
          description = "sourcehut ${serviceName} service";
          # So that extraServices have the PostgreSQL database initialized.
          after = [ "${srvsrht}.service" ];
          requiredBy = [ "${srvsrht}.service" ];
          serviceConfig = {
            Type = "simple";
            Restart = mkDefault "always";
          };
        }
        extraService
      ])) extraServices)
    ];

    systemd.timers = mapAttrs (timerName: timer:
      {
        description = "sourcehut timer for ${timerName}";
        wantedBy = [ "timers.target" ];
        inherit (timer) timerConfig;
      }) extraTimers;
  } ]);
}