nix: move dev outputs to subflake

nix/module.nix

@@ -0,0 +1,149 @@
+self: {
+  config,
+  lib,
+  pkgs,
+  ...
+}: let
+  cfg = config.services.refraction;
+  defaultUser = "refraction";
+
+  inherit
+    (lib)
+    getExe
+    literalExpression
+    mdDoc
+    mkEnableOption
+    mkIf
+    mkOption
+    mkPackageOption
+    optionals
+    types
+    ;
+in {
+  options.services.refraction = {
+    enable = mkEnableOption "refraction";
+    package = mkPackageOption self.packages.${pkgs.stdenv.hostPlatform.system} "refraction" {};
+
+    user = mkOption {
+      description = mdDoc ''
+        User under which the service should run. If this is the default value,
+        the user will be created, with the specified group as the primary
+        group.
+      '';
+      type = types.str;
+      default = defaultUser;
+      example = literalExpression ''
+        "bob"
+      '';
+    };
+
+    group = mkOption {
+      description = mdDoc ''
+        Group under which the service should run. If this is the default value,
+        the group will be created.
+      '';
+      type = types.str;
+      default = defaultUser;
+      example = literalExpression ''
+        "discordbots"
+      '';
+    };
+
+    redisUrl = mkOption {
+      description = mdDoc ''
+        Connection to a redis server. If this needs to include credentials
+        that shouldn't be world-readable in the Nix store, set environmentFile
+        and override the `REDIS_URL` entry.
+        Pass the string `local` to setup a local Redis database.
+      '';
+      type = types.str;
+      default = "local";
+      example = literalExpression ''
+        "redis://localhost/"
+      '';
+    };
+
+    environmentFile = mkOption {
+      description = mdDoc ''
+        Environment file as defined in {manpage}`systemd.exec(5)`
+      '';
+      type = types.nullOr types.path;
+      default = null;
+      example = literalExpression ''
+        "/run/agenix.d/1/refraction"
+      '';
+    };
+  };
+
+  config = mkIf cfg.enable {
+    services.redis.servers.refraction = mkIf (cfg.redisUrl == "local") {
+      enable = true;
+      inherit (cfg) user;
+      port = 0; # disable tcp listener
+    };
+
+    systemd.services."refraction" = {
+      enable = true;
+      wantedBy = ["multi-user.target"];
+      after =
+        ["network.target"]
+        ++ optionals (cfg.redisUrl == "local") ["redis-refraction.service"];
+
+      script = ''
+        ${getExe cfg.package}
+      '';
+
+      environment = {
+        BOT_REDIS_URL =
+          if cfg.redisUrl == "local"
+          then "unix:${config.services.redis.servers.refraction.unixSocket}"
+          else cfg.redisUrl;
+      };
+
+      serviceConfig = {
+        Type = "simple";
+        Restart = "on-failure";
+
+        EnvironmentFile = mkIf (cfg.environmentFile != null) cfg.environmentFile;
+
+        User = cfg.user;
+        Group = cfg.group;
+
+        # hardening
+        NoNewPrivileges = true;
+        PrivateDevices = true;
+        PrivateTmp = true;
+        PrivateUsers = true;
+        ProtectClock = true;
+        ProtectControlGroups = true;
+        ProtectHome = true;
+        ProtectHostname = true;
+        ProtectKernelLogs = true;
+        ProtectKernelModules = true;
+        ProtectKernelTunables = true;
+        ProtectSystem = "strict";
+        RestrictNamespaces = true;
+        RestrictSUIDSGID = true;
+        SystemCallArchitectures = "native";
+        SystemCallFilter = [
+          "@system-service"
+          "~@resources"
+          "~@privileged"
+        ];
+      };
+    };
+
+    users = {
+      users = mkIf (cfg.user == defaultUser) {
+        ${defaultUser} = {
+          isSystemUser = true;
+          inherit (cfg) group;
+        };
+      };
+
+      groups = mkIf (cfg.group == defaultUser) {
+        ${defaultUser} = {};
+      };
+    };
+  };
+}