{
  config,
  libNginx,
  lib,
  ...
}:
with lib; let
  cfg = config.nixfiles.modules.prometheus;
in {
  options.nixfiles.modules.prometheus = {
    enable = mkEnableOption "Prometheus";

    port = mkOption {
      description = "Port.";
      type = with types; port;
      default = 30111;
    };

    domain = mkOption {
      description = "Domain name sans protocol scheme.";
      type = with types; str;
      default = "prometheus.${config.networking.domain}";
    };
  };

  config = mkIf cfg.enable {
    nixfiles.modules.nginx = with cfg; {
      enable = true;
      upstreams.prometheus.servers."127.0.0.1:${toString cfg.port}" = {};
      virtualHosts.${domain} = {
        locations."/".proxyPass = "http://prometheus";
        extraConfig = libNginx.config.internalOnly;
      };
    };

    services.prometheus = with cfg; {
      enable = true;
      enableReload = true;

      listenAddress = "127.0.0.1";
      inherit port;

      extraFlags = [
        "--web.external-url=https://${domain}"
        "--storage.tsdb.retention.size=50GB"
        "--storage.tsdb.retention.time=1y"
        "--storage.tsdb.wal-compression"
      ];
    };
  };
}