{ lib, entities, ... }:

with lib;
let
  getHostSite = hostname:
    let site-name = entities.hosts."${hostname}".site;
    in entities.sites."${site-name}";
  getHostDomain = hostname:
    let domain-name = entities.hosts."${hostname}".domain;
    in entities.domains."${domain-name}";
  getHostRealm = hostname: (getHostDomain hostname).gssapi-realm;
  getHostFqdn = hostname:
    let hostDomain = entities.hosts."${hostname}".domain;
    in "${hostname}.${hostDomain}";

  getHostNetworkSettings = hostname:
    let
      hostDomain = entities.hosts."${hostname}".domain;
      hostNetwork = entities.zones."${hostDomain}";
    in hostNetwork.hosts."${hostname}";

  getIfAttr = as: a: if hasAttr as a then getAttr as a else null;

  getHostIpv4 = hostname:
    getIfAttr "ipv4-address" (getHostNetworkSettings hostname);
  getHostIpv6 = hostname:
    getIfAttr "ipv6-address" (getHostNetworkSettings hostname);
  getHostIps = hostname:
    filter (o: o != null) [ (getHostIpv4 hostname) (getHostIpv6 hostname) ];

  getDomainPostgresqlServer = domain:
    getHostFqdn entities.domains."${domain}".postgresql-server;

  getSiteHosts = site:
    attrNames (filterAttrs (_: hostOpts: hostOpts.site == site) entities.hosts);
  getDomainHosts = domain:
    attrNames
    (filterAttrs (_: hostOpts: hostOpts.domain == domain) entities.hosts);

  getSiteGatewayV4 = siteName:
    let site = entities.sites."${siteName}";
    in if hasAttr "local-gateway" site then
      getHostIpv4 site.local-gateway
    else
      site.gateway-v4;

  getHostGatewayV4 = hostname:
    getSiteGatewayV4 entities.hosts."${hostname}".site;

  getSiteGatewayV6 = siteName:
    let site = entities.sites."${siteName}";
    in if hasAttr "local-gateway" site then
      getHostIpv6 site.local-gateway
    else
      site.gateway-v6;

  getHostGatewayV6 = hostname:
    getSiteGatewayV6 entities.hosts."${hostname}".site;

  getSiteNetwork = siteName: entities.sites."${siteName}".network;

  getSiteV4PrefixLength = siteName:
    toInt (elemAt (splitString "/" (getSiteNetwork siteName)));

  getSiteV6PrefixLength = siteName:
    abort "not implemented: getSiteV6PrefixLength";

in {
  inherit getHostSite getHostDomain getHostRealm getHostFqdn getHostIpv4
    getHostIpv6 getHostIps getDomainPostgresqlServer getSiteHosts getDomainHosts
    getSiteGatewayV4 getHostGatewayV4 getSiteGatewayV6 getHostGatewayV6
    getSiteV4PrefixLength getSiteV6PrefixLength;

  fudo-types = with lib.types; {
    networkHost.options = {
      hostname = mkOption {
        type = str;
        description = "Hostname";
      };

      ipv4-address = mkOption {
        type = nullOr str;
        description = "The V4 IP of a given host, if any.";
        default = null;
      };

      ipv6-address = mkOption {
        type = nullOr str;
        description = "The V6 IP of a given host, if any.";
        default = null;
      };

      mac-address = mkOption {
        type = nullOr str;
        description =
          "The MAC address of a given host, if desired for IP reservation.";
        default = null;
      };

      description = mkOption {
        type = nullOr str;
        description = "Description of the host.";
        default = null;
      };

      sshfp-records = mkOption {
        type = listOf str;
        description = "List of SSHFP records for this host.";
        default = [ ];
      };
    };

    networkHosts = let
      # This is necessary because of the default 'name'...sigh.
      networkHostOpt = { name, ... }: {
        options = {
          hostname = mkOption {
            type = str;
            description = "Hostname";
            default = name;
          };

          ipv4-address = mkOption {
            type = nullOr str;
            description = "The V4 IP of a given host, if any.";
            default = null;
          };

          ipv6-address = mkOption {
            type = nullOr str;
            description = "The V6 IP of a given host, if any.";
            default = null;
          };

          mac-address = mkOption {
            type = nullOr str;
            description =
              "The MAC address of a given host, if desired for IP reservation.";
            default = null;
          };

          description = mkOption {
            type = nullOr str;
            description = "Description of the host.";
            default = null;
          };

          sshfp-records = mkOption {
            type = listOf str;
            description = "List of SSHFP records for this host.";
            default = [ ];
          };
        };
      };
    in attrsOf (submodule networkHostOpt);
  };
}