grobi: add module

This adds a service module for [grobi](https://github.com/fd0/grobi),
which can be used to automatically configure monitors/outputs for Xorg
via RANDR.

modules/misc/news.nix

@@ -1303,6 +1303,14 @@ in
           A new module is available: 'xsession.windowManager.bspwm'.
         '';
       }
+
+      {
+        time = "2020-01-26T12:49:40+00:00";
+        condition = hostPlatform.isLinux;
+        message = ''
+          A new module is available: 'services.grobi'.
+        '';
+      }
     ];
   };
 }

modules/modules.nix

@@ -115,6 +115,7 @@ let
     (loadModule ./services/getmail.nix { condition = hostPlatform.isLinux; })
     (loadModule ./services/gnome-keyring.nix { })
     (loadModule ./services/gpg-agent.nix { })
+    (loadModule ./services/grobi.nix { condition = hostPlatform.isLinux; })
     (loadModule ./services/hound.nix { condition = hostPlatform.isLinux; })
     (loadModule ./services/imapnotify.nix { condition = hostPlatform.isLinux; })
     (loadModule ./services/kbfs.nix { })

modules/services/grobi.nix

@@ -0,0 +1,101 @@
+{ config, lib, pkgs, ... }:
+
+with lib;
+
+let
+
+  cfg = config.services.grobi;
+
+  eitherStrBoolIntList =
+    with types; either str (either bool (either int (listOf str)));
+
+in
+
+{
+  meta.maintainers = [ maintainers.mbrgm ];
+
+  options = {
+    services.grobi = {
+      enable = mkEnableOption "the grobi display setup daemon";
+
+      executeAfter = mkOption {
+        type = with types; listOf str;
+        default = [];
+        example = [ "setxkbmap dvorak" ];
+        description = ''
+          Commands to be run after an output configuration was
+          changed. The Nix value declared here will be translated to
+          JSON and written to the <option>execute_after</option> key
+          in <filename>~/.config/grobi.conf</filename>.
+        '';
+      };
+
+      rules = mkOption {
+        type = with types; listOf (attrsOf eitherStrBoolIntList);
+        default = [];
+        example = literalExample ''
+          [
+            {
+              name = "Home";
+              outputs_connected = [ "DP-2" ];
+              configure_single = "DP-2";
+              primary = true;
+              atomic = true;
+              execute_after = [
+                "${pkgs.xorg.xrandr}/bin/xrandr --dpi 96"
+                "${pkgs.xmonad-with-packages}/bin/xmonad --restart";
+              ];
+            }
+            {
+              name = "Mobile";
+              outputs_disconnected = [ "DP-2" ];
+              configure_single = "eDP-1";
+              primary = true;
+              atomic = true;
+              execute_after = [
+                "${pkgs.xorg.xrandr}/bin/xrandr --dpi 120"
+                "${pkgs.xmonad-with-packages}/bin/xmonad --restart";
+              ];
+            }
+          ]
+        '';
+        description = ''
+          These are the rules grobi tries to match to the current
+          output configuration. The rules are evaluated top to bottom,
+          the first matching rule is applied and processing stops. See
+          <link xlink:href="https://github.com/fd0/grobi/blob/master/doc/grobi.conf"/>
+          for more information. The Nix value declared here will be
+          translated to JSON and written to the <option>rules</option>
+          key in <filename>~/.config/grobi.conf</filename>.
+        '';
+      };
+    };
+  };
+
+  config = mkIf cfg.enable {
+    systemd.user.services.grobi = {
+      Unit = {
+        Description = "grobi display auto config daemon";
+        After = [ "graphical-session-pre.target" ];
+        PartOf = [ "graphical-session.target" ];
+      };
+
+      Service = {
+        Type = "simple";
+        ExecStart = "${pkgs.grobi}/bin/grobi watch -v";
+        Restart = "always";
+        RestartSec = "2s";
+        Environment = "PATH=${pkgs.xorg.xrandr}/bin:${pkgs.bash}/bin";
+      };
+
+      Install = {
+        WantedBy = [ "graphical-session.target" ];
+      };
+    };
+
+    xdg.configFile."grobi.conf".text = builtins.toJSON {
+      execute_after = cfg.executeAfter;
+      rules = cfg.rules;
+    };
+  };
+}