feat: expand systemd notify service with libnotify option

modules/emailNotify.nix

@@ -1,67 +0,0 @@
-{ config, lib, pkgs, ... }:
-
-with lib;
-
-let
-  cfg = config.systemd.emailNotify;
-  sendmail = pkgs.writeScript "sendmail" ''
-    #!${pkgs.runtimeShell}
-
-    ${pkgs.system-sendmail}/bin/sendmail -t <<ERRMAIL
-    To: ${cfg.mailTo}
-    From: ${cfg.mailFrom}
-    Subject: Status of service $1
-    Content-Transfer-Encoding: 8bit
-    Content-Type: text/plain; charset=UTF-8
-    $(systemctl status --full "$1")
-    ERRMAIL
-  '';
-in {
-  options = {
-    systemd.emailNotify = {
-      enable = mkOption {
-        type = types.bool;
-        default = false;
-        description =
-          "Whether to enable email notification for failed services.";
-      };
-
-      mailTo = mkOption {
-        type = types.str;
-        default = null;
-        description =
-          "Email address to which the service status will be mailed.";
-      };
-
-      mailFrom = mkOption {
-        type = types.str;
-        default = null;
-        description =
-          "Email address from which the service status will be mailed.";
-      };
-    };
-
-    systemd.services = mkOption {
-      type = with types;
-        attrsOf (submodule {
-          config.onFailure = optional cfg.enable "email@%n.service";
-        });
-    };
-  };
-
-  config = mkIf cfg.enable {
-    assertions = singleton {
-      assertion = cfg.mailTo != null && cfg.mailFrom != null;
-      message = "You need to specify a sender and a receiver";
-    };
-
-    systemd.services."email@" = {
-      description = "Sends a status mail via sendmail on service failures.";
-      onFailure = lib.mkForce [ ];
-      serviceConfig = {
-        ExecStart = "${sendmail} %i";
-        Type = "oneshot";
-      };
-    };
-  };
-}

modules/systemdNotify.nix

@@ -0,0 +1,108 @@
+{ config, lib, pkgs, ... }:
+
+with lib;
+
+# TODO replace with more secure service, e.g. matrix-sendmail (matrix-commander)
+# needs to support queueing
+# flake: https://github.com/emmanuelrosa/erosanix/blob/master/modules/matrix-sendmail.nix
+# call `matrix-commander --login` with credentials on service start
+let
+  cfg = config.systemd.notify;
+  sendmail = pkgs.writeScript "sendmail" ''
+    #!${pkgs.runtimeShell}
+
+    ${pkgs.system-sendmail}/bin/sendmail -t <<ERRMAIL
+    To: ${cfg.email.mailTo}
+    From: ${cfg.email.mailFrom}
+    Subject: Service $1 failed
+    Content-Transfer-Encoding: 8bit
+    Content-Type: text/plain; charset=UTF-8
+
+    $(systemctl status --full "$1")
+    ERRMAIL
+  '';
+in {
+  options = {
+    systemd.notify = {
+      enable = mkOption {
+        type = types.bool;
+        default = false;
+        description = "Whether to enable notifications for failed services.";
+      };
+
+      method = mkOption {
+        type = types.enum [ "libnotify" "email" ];
+        default = "libnotify";
+        description = "The method for sending notifications.";
+      };
+
+      libnotify.user = mkOption {
+        type = types.str;
+        default = null;
+        description = "User session to which the notification will be sent.";
+      };
+
+      email.mailTo = mkOption {
+        type = types.str;
+        default = null;
+        description =
+          "Email address to which the service status will be mailed.";
+      };
+
+      email.mailFrom = mkOption {
+        type = types.str;
+        default = null;
+        description =
+          "Email address from which the service status will be mailed.";
+      };
+    };
+
+    systemd.services = mkOption {
+      type = with types;
+        attrsOf (submodule {
+          config.onFailure = optional cfg.enable "notify@%n.service";
+        });
+    };
+  };
+
+  config = mkIf cfg.enable {
+    assertions = [
+      {
+        assertion = cfg.method != "libnotify" || cfg.libnotify.user != null;
+        message = "You need to specify a user";
+      }
+      {
+        assertion = cfg.method != "email"
+          || (cfg.email.mailTo != null && cfg.email.mailFrom != null);
+        message = "You need to specify a sender and a receiver";
+      }
+    ];
+
+    systemd.services."notify@" = {
+      onFailure = lib.mkForce [ ];
+    } // optionalAttrs (cfg.method == "libnotify") {
+      description = "Desktop notifications for %i service failure";
+      environment = {
+        DBUS_SESSION_BUS_ADDRESS = "unix:path=/run/user/${
+            toString config.users.users.${cfg.libnotify.user}.uid
+          }/bus";
+        INSTANCE = "%i";
+      };
+      script = ''
+        ${pkgs.libnotify}/bin/notify-send --urgency=critical \
+          "Service '$INSTANCE' failed" \
+          "$(journalctl -n 6 -o cat -u $INSTANCE)"
+      '';
+      serviceConfig = {
+        Type = "oneshot";
+        User = cfg.libnotify.user;
+      };
+    } // optionalAttrs (cfg.method == "email") {
+      description = "E-Mail notifications for %i service failure";
+      serviceConfig = {
+        ExecStart = "${sendmail} %i";
+        Type = "oneshot";
+      };
+    };
+  };
+}