{ lib, pkgs, config, ... }:
{
  services.grafana.provision.alerting.rules.settings.groups = [
    {
      name = "InodeUsageAlerts";
      folder = "System Alerts";
      interval = "1m";

      rules = [
        {
          uid = "high-inode-usage-alert-uid";
          title = "HighInodeUsage";
          condition = "D"; # Condition is now D

          data = [
            # Query A: Calculate inode usage percentage
            {
              refId = "A";
              datasourceUid = "vm-datasource-uid";
              queryType = "prometheus";
              relativeTimeRange = { from = 60; to = 0; };
              model = {
                expr = ''
                  (
                    node_filesystem_files{fstype!~"tmpfs|rootfs",mountpoint!=""} - node_filesystem_files_free{fstype!~"tmpfs|rootfs",mountpoint!=""}
                  ) / (node_filesystem_files{fstype!~"tmpfs|rootfs",mountpoint!=""} > 0) * 100
                  and node_filesystem_files{fstype!~"tmpfs|rootfs",mountpoint!=""}
                  and node_filesystem_files_free{fstype!~"tmpfs|rootfs",mountpoint!=""}
                '';
                legendFormat = "{{mountpoint}} on {{instance}}";
                instant = false;
              };
            }
            # Expression C: Reduce Query A to its last value, preserving labels
            {
              refId = "C";
              datasourceUid = "__expr__";
              model = {
                type = "reduce";
                expression = "A"; # Input is Query A
                reducer = "last"; # Get the last value of each series in A
              };
            }
            # Expression D: Apply math condition to the reduced values from C
            {
              refId = "D";
              datasourceUid = "__expr__";
              model = {
                type = "math";
                expression = "$C > 80"; # Alert if inode usage from C is > 80%
              };
            }
          ];

          for = "30m"; # Duration the condition must be met
          noDataState = "NoData";
          execErrState = "Error";

          annotations = {
            summary = "High inode usage on {{ $labels.instance }} at {{ $labels.mountpoint }}";
            description = ''Inode usage on {{ $labels.instance }} for mount point {{ $labels.mountpoint }} (fstype: {{ $labels.fstype }}) has been above 80% for more than 30 minutes. Current value: {{ if $values.C }}{{ $values.C | humanizePercentage }}{{ else }}N/A{{ end }}%.'';
          };
          labels = {
            severity = "warning";
            category = "capacity";
          };
        }
      ];
    }
  ];
}