{ config, lib, pkgs, ... }:

with lib;
let
  hostname = config.instance.hostname;

  domain-name = config.fudo.hosts.${hostname}.domain;
  site-name = config.fudo.hosts.${hostname}.site;
  zone-name = config.fudo.domains.${domain-name}.zone;

  site = config.fudo.sites.${site-name};

  cfg = config.fudo.services.local-network;

  resolverOpts = {
    options = {
      ip = mkOption {
        type = str;
        description = "IP address of the upstream recursive resolver.";
        default = "1.1.1.1";
      };

      port = mkOption {
        type = port;
        description = "Port of DNS server on the recursive resolver.";
        default = 53;
      };
    };
  };

in {
  options.fudo.services.local-network = with types; {
    enable = mkEnableOption "Enable local network server.";

    internal-interfaces = mkOption {
      type = listOf str;
      description = ''
        Interfaces on which to:

        * Accept NAT traffic
        * Serve DNS
        * Serve DHCP
      '';
    };

    external-interface = mkOption {
      type = str;
      description = "Interface facing the larger internet.";
      example = "extif0";
    };

    resolvers = mkOption {
      type = listOf (submodule resolverOpts);
      description = "List of upstream DNS servers.";
      default = [
        { ip = "1.1.1.1"; }
        { ip = "1.0.0.1"; }
        { ip = "9.9.9.9"; }
        { ip = "149.112.112.112"; }
      ];
    };

    dns-filter-proxy = {
      enable = mkEnableOption "Enable DNS filter.";

      http-listen-port = mkOption {
        type = port;
        description = "Port on localhost on which to listen for HTTP requests.";
        default = 4080;
      };

      http-host-alias = mkOption {
        type = str;
        description = "Host alias for the DNS filter server.";
        default = "dns-filter";
      };

      dns-listen-port = mkOption {
        type = port;
        description = "Port on localhost on which to listen for DNS requests.";
        default = 4053;
      };

      upstream-dns = mkOption {
        type = listOf str;
        description = "List of upstream DNS-over-HTTPS endpoints.";
        default = [
          "https://1.1.1.1/dns-query"
          "https://1.0.0.1/dns-query"
          # These 11 addrs send the network, so the response can prefer closer answers
          "https://9.9.9.11/dns-query"
          "https://149.112.112.11/dns-query"
          "https://2620:fe::11/dns-query"
          "https://2620:fe::fe:11/dns-query"
        ];
      };
    };
  };

  config = mkIf (site.local-gateway != null) (let
    host-ipv4 = pkgs.lib.network.host-ipv4 config;
    gateway-host =  site.local-gateway;
    nameserver-host = gateway-host;
    gateway-ip = host-ipv4 gateway-host;
    nameserver-ip = host-ipv4 gateway-host;
    is-gateway = hostname == gateway-host;
    agp = cfg.dns-filter-proxy;
    fqdn = hostname: "${hostname}.${domain-name}.";
  in {
    networking = {
      nat = mkIf is-gateway {
        enable = true;
        externalInterface = cfg.external-interface;
        internalInterfaces = cfg.internal-interfaces;
      };

      nameservers = [ nameserver-ip ];

      firewall = if is-gateway then {
        enable = true;
        trustedInterfaces = cfg.internal-interfaces;
      } else {
        enable = false;
      };
    };

    fudo = {
      adguard-dns-proxy = mkIf agp.enable {
        enable = true;
        http = {
          listen-ip = "127.0.0.1";
          listen-port = agp.http-listen-port;
        };
        dns = {
          listen-ips = [ "127.0.0.1" ];
          listen-port = agp.dns-listen-port;
        };
        local-domain-name = domain-name;
      };

      zones.${zone-name} = {
        aliases = {
          ${agp.http-host-alias} = optionalAttrs (agp.enable)
            (fqdn gateway-host);
          ns = (fqdn nameserver-host);
          gw = (fqdn gateway-host);
        };

        hosts = {
          gateway.ipv4-address = gateway-ip;
          nameserver.ipv4-address = nameserver-ip;
        };

        nameservers = [
          "nameserver"
        ];

        srv-records = {
          tcp.domain = [{
            host = "nameserver.${domain-name}";
            port = 53;
          }];
          udp.domain = [{
            host = "nameserver.${domain-name}";
            port = 53;
          }];
        };
      };

      local-network = {
        enable = is-gateway;
        domain = domain-name;
        dns-servers = [ nameserver-ip ];
        gateway = gateway-ip;
        dhcp-interfaces = cfg.internal-interfaces;
        dns-listen-ips = optionals is-gateway [ nameserver-ip "127.0.0.1" "127.0.1.1" ];
        dns-listen-ipv6s = optionals (is-gateway && config.networking.enableIPv6) [ "::1" ];
        recursive-resolver = if agp.enable then {
          host = "127.0.0.1";
          port = agp.dns-listen-port;
        } else {
          host = cfg.resolver.ip;
          port = cfg.resolver.port;
        };
        network = site.network;
        dhcp-dynamic-network = site.dynamic-network;
        search-domains = [ domain-name "fudo.org" ];
        enable-reverse-mappings = true;
        zone-definition = config.fudo.zones.${zone-name};
      };
    };

    services.nginx = mkIf agp.enable {
      enable = true;
      recommendedGzipSettings = true;
      recommendedOptimisation = true;
      recommendedProxySettings = true;

      virtualHosts = {
        "${agp.http-host-alias}.${domain-name}" = {
          locations."/".proxyPass =
            "http://127.0.0.1:${toString agp.http-listen-port}";
        };
      };
    };
  });
}