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

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

          data = [
            # Query A: Calculate CPU usage percentage
            {
              refId = "A";
              datasourceUid = "vm-datasource-uid";
              queryType = "prometheus";
              relativeTimeRange = { from = 60; to = 0; }; # Query over the last minute
              model = {
                # Calculate average CPU usage over 1m, grouped by instance and job
                expr = ''(1 - avg by (instance, job) (rate(node_cpu_seconds_total{mode="idle"}[1m]))) * 100'';
                legendFormat = "CPU usage on {{instance}} ({{job}})";
                instant = false; # This is a range query
              };
            }
            # 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 > 90"; # Alert if CPU usage from C is > 90%
              };
            }
          ];

          for = "5m"; # Duration the condition must be met
          noDataState = "NoData";
          execErrState = "Error";

          annotations = {
            summary = "High CPU usage on {{ $labels.instance }}";
            description = ''CPU usage on {{ $labels.instance }} (job: {{ $labels.job }}) has been above 90% for more than 5 minutes. Current value: {{ if $values.C }}{{ $values.C | humanizePercentage }}{{ else }}N/A{{ end }}%.'';
          };
          labels = {
            severity = "warning";
            category = "performance";
          };
        }
      ];
    }
  ];
}