grafana: re-organize

services/grafana/disk-usage-collector.nix

@@ -0,0 +1,38 @@
+{
+  config,
+  pkgs,
+  lib,
+  ...
+}:
+let
+  textfileDir = "/var/lib/prometheus-node-exporter-textfiles";
+
+  diskUsageCollector = pkgs.writeShellApplication {
+    name = "disk-usage-collector";
+    runtimeInputs = with pkgs; [
+      coreutils
+      gawk
+      config.boot.zfs.package
+      util-linux # for mountpoint
+    ];
+    text = builtins.readFile ./disk-usage-collector.sh;
+  };
+in
+lib.mkIf config.services.grafana.enable {
+  systemd.services.disk-usage-collector = {
+    description = "Collect ZFS pool and partition usage metrics for Prometheus";
+    serviceConfig = {
+      Type = "oneshot";
+      ExecStart = lib.getExe diskUsageCollector;
+    };
+    environment.TEXTFILE = "${textfileDir}/disk-usage.prom";
+  };
+
+  systemd.timers.disk-usage-collector = {
+    wantedBy = [ "timers.target" ];
+    timerConfig = {
+      OnCalendar = "minutely";
+      RandomizedDelaySec = "10s";
+    };
+  };
+}