{
  lib,
  pkgs,
  config,
  nodes,
  ...
}:
let
  inherit (config.lib) ports;
  targets = lib.mapAttrsToList (_name: node: node.fqdn) nodes ++ [ "pek0.ny4.dev" ];
in
{
  services.prometheus = {
    enable = true;
    listenAddress = "127.0.0.1";
    port = ports.prometheus;
    webExternalUrl = "https://prom.ny4.dev";

    exporters.blackbox = {
      enable = true;
      listenAddress = "127.0.0.1";
      port = ports.blackbox;
      configFile = (pkgs.formats.yaml { }).generate "config.yaml" {
        modules.http_2xx = {
          prober = "http";
          http.fail_if_not_ssl = true;
        };
      };
    };

    scrapeConfigs = [
      {
        job_name = "node_exporter";
        metrics_path = "/metrics";
        basic_auth = {
          username = "prometheus";
          password_file = config.sops.secrets."prometheus/auth".path;
        };
        static_configs = lib.singleton { inherit targets; };
      }
      {
        job_name = "caddy";
        metrics_path = "/caddy";
        basic_auth = {
          username = "prometheus";
          password_file = config.sops.secrets."prometheus/auth".path;
        };
        static_configs = lib.singleton { inherit targets; };
      }
      {
        job_name = "blackbox_exporter";
        static_configs = lib.singleton { targets = [ "127.0.0.1:${toString ports.blackbox}" ]; };
      }
      {
        job_name = "blackbox_probe";
        metrics_path = "/probe";
        params = {
          module = [ "http_2xx" ];
        };
        static_configs = lib.singleton {
          targets = [
            "https://blog.ny4.dev"
            "https://cinny.ny4.dev"
            "https://element.ny4.dev"
            "https://git.ny4.dev"
            "https://id.ny4.dev"
            "https://mastodon.ny4.dev"
            "https://matrix.ny4.dev"
            "https://ntfy.ny4.dev"
            "https://pb.ny4.dev"
            "https://reddit.ny4.dev"
            "https://rss.ny4.dev"
            "https://vault.ny4.dev"
          ];
        };
        relabel_configs = [
          {
            source_labels = [ "__address__" ];
            target_label = "__param_target";
          }
          {
            source_labels = [ "__param_target" ];
            target_label = "instance";
          }
          {
            target_label = "__address__";
            replacement = "127.0.0.1:${toString ports.blackbox}";
          }
        ];
      }

    ];

    rules = lib.singleton (
      builtins.toJSON {
        groups = lib.singleton {
          name = "metrics";
          rules = [
            {
              alert = "NodeDown";
              expr = ''up{job="node_exporter"} == 0'';
              for = "5m";
              annotations = {
                summary = "Node exporter down on {{ $labels.instance }}";
                description = "Node exporter on {{ $labels.instance }} has been down for more than 5 minutes.";
              };
            }
            {
              alert = "HTTPDown";
              expr = ''up{job="blackbox_probe"} == 0 or probe_success{job="blackbox_probe"} == 0'';
              for = "5m";
              annotations = {
                summary = "HTTP probe failure on {{ $labels.instance }}";
                description = "The HTTP blackbox probe on {{ $labels.instance }} has failed for more than 5 minutes.";
              };
            }
            {
              alert = "MemoryFull";
              expr = ''node_memory_MemAvailable_bytes / node_memory_MemTotal_bytes < 0.1'';
              for = "5m";
              annotations = {
                summary = "Low available memory on {{ $labels.instance }}";
                description = "{{ $labels.instance }} has less than 10% available memory for more than 5 minutes.";
              };
            }
            {
              alert = "DiskFull";
              expr = ''node_filesystem_avail_bytes{mountpoint=~"/|/persist|/mnt"} / node_filesystem_size_bytes < 0.1'';
              annotations = {
                summary = "Low disk space on {{ $labels.instance }}";
                description = "The disk {{ $labels.device }} mounted at {{ $labels.mountpoint }} on {{ $labels.instance }} has less than 10% of empty space available.";
              };
            }
            {
              alert = "UnitFailed";
              expr = ''node_systemd_unit_state{state="failed"} == 1'';
              annotations = {
                summary = "Systemd unit {{ $labels.name }} failure on {{ $labels.instance }}";
                description = "The systemd unit {{ $labels.name }} on {{ $labels.instance }} has entered a {{ $labels.state }} state.";
              };
            }
          ];
        };
      }
    );

    alertmanagers = lib.singleton {
      static_configs = lib.singleton { targets = [ "127.0.0.1:${toString ports.alertmanager}" ]; };
    };

    alertmanager = {
      enable = true;
      listenAddress = "127.0.0.1";
      port = ports.alertmanager;

      configuration = {
        receivers = lib.singleton {
          name = "ntfy";
          webhook_configs = lib.singleton {
            # https://docs.ntfy.sh/publish/#message-templating
            url =
              let
                tmpl = lib.escapeURL ''
                  {{ range .alerts }}- Status: {{ .status }}
                    Summary: {{ .annotations.summary }}
                    Description: {{ .annotations.description }}
                    Source: {{ .generatorURL }}
                  {{ end }}
                '';
              in
              "https://ntfy.ny4.dev/alert?tpl=yes&md=yes&m=${tmpl}";
          };
        };
        route = {
          receiver = "ntfy";
        };
      };
    };
  };

  services.caddy.settings.apps.http.servers.srv0.routes = lib.singleton {
    match = lib.singleton { host = [ "prom.ny4.dev" ]; };
    handle = lib.singleton {
      handler = "reverse_proxy";
      upstreams = [ { dial = "127.0.0.1:${toString ports.prometheus}"; } ];
    };
  };
}