nixos-servers/lib/monitoring.nix

{ lib }:
let
  # Extract IP address from CIDR notation (e.g., "10.69.13.5/24" -> "10.69.13.5")
  extractIP = address:
    let
      parts = lib.splitString "/" address;
    in
    builtins.head parts;

  # Check if a network interface name looks like a VPN/tunnel interface
  isVpnInterface = ifaceName:
    lib.hasPrefix "wg" ifaceName ||
    lib.hasPrefix "tun" ifaceName ||
    lib.hasPrefix "tap" ifaceName ||
    lib.hasPrefix "vti" ifaceName;

  # Extract monitoring info from a single host configuration
  # Returns null if host should not be included
  extractHostMonitoring = name: hostConfig:
    let
      cfg = hostConfig.config;
      monConfig = (cfg.homelab or { }).monitoring or { enable = true; scrapeTargets = [ ]; };
      dnsConfig = (cfg.homelab or { }).dns or { enable = true; };
      hostname = cfg.networking.hostName;
      networks = cfg.systemd.network.networks or { };

      # Filter out VPN interfaces and find networks with static addresses
      physicalNetworks = lib.filterAttrs
        (netName: netCfg:
          let
            ifaceName = netCfg.matchConfig.Name or "";
          in
          !(isVpnInterface ifaceName) && (netCfg.address or [ ]) != [ ])
        networks;

      # Get addresses from physical networks only
      networkAddresses = lib.flatten (
        lib.mapAttrsToList
          (netName: netCfg: netCfg.address or [ ])
          physicalNetworks
      );

      firstAddress = if networkAddresses != [ ] then builtins.head networkAddresses else null;
    in
    if !(monConfig.enable or true) || !(dnsConfig.enable or true) || firstAddress == null then
      null
    else
      {
        inherit hostname;
        ip = extractIP firstAddress;
        scrapeTargets = monConfig.scrapeTargets or [ ];
      };

  # Generate node-exporter targets from all flake hosts
  generateNodeExporterTargets = self: externalTargets:
    let
      nixosConfigs = self.nixosConfigurations or { };
      hostList = lib.filter (x: x != null) (
        lib.mapAttrsToList extractHostMonitoring nixosConfigs
      );
      flakeTargets = map (host: "${host.hostname}.home.2rjus.net:9100") hostList;
    in
    flakeTargets ++ (externalTargets.nodeExporter or [ ]);

  # Generate scrape configs from all flake hosts and external targets
  generateScrapeConfigs = self: externalTargets:
    let
      nixosConfigs = self.nixosConfigurations or { };
      hostList = lib.filter (x: x != null) (
        lib.mapAttrsToList extractHostMonitoring nixosConfigs
      );

      # Collect all scrapeTargets from all hosts, grouped by job_name
      allTargets = lib.flatten (map
        (host:
          map
            (target: {
              inherit (target) job_name port metrics_path scheme scrape_interval honor_labels;
              hostname = host.hostname;
            })
            host.scrapeTargets
        )
        hostList
      );

      # Group targets by job_name
      grouped = lib.groupBy (t: t.job_name) allTargets;

      # Generate a scrape config for each job
      flakeScrapeConfigs = lib.mapAttrsToList
        (jobName: targets:
          let
            first = builtins.head targets;
            targetAddrs = map
              (t:
                let
                  portStr = toString t.port;
                in
                "${t.hostname}.home.2rjus.net:${portStr}")
              targets;
            config = {
              job_name = jobName;
              static_configs = [{
                targets = targetAddrs;
              }];
            }
            // (lib.optionalAttrs (first.metrics_path != "/metrics") {
              metrics_path = first.metrics_path;
            })
            // (lib.optionalAttrs (first.scheme != "http") {
              scheme = first.scheme;
            })
            // (lib.optionalAttrs (first.scrape_interval != null) {
              scrape_interval = first.scrape_interval;
            })
            // (lib.optionalAttrs first.honor_labels {
              honor_labels = true;
            });
          in
          config
        )
        grouped;

      # External scrape configs
      externalScrapeConfigs = map
        (ext: {
          job_name = ext.job_name;
          static_configs = [{
            targets = ext.targets;
          }];
        } // (lib.optionalAttrs (ext ? metrics_path) {
          metrics_path = ext.metrics_path;
        }) // (lib.optionalAttrs (ext ? scheme) {
          scheme = ext.scheme;
        }) // (lib.optionalAttrs (ext ? scrape_interval) {
          scrape_interval = ext.scrape_interval;
        }))
        (externalTargets.scrapeConfigs or [ ]);
    in
    flakeScrapeConfigs ++ externalScrapeConfigs;

in
{
  inherit extractHostMonitoring generateNodeExporterTargets generateScrapeConfigs;
}