# This module automatically discovers zones in BIND and NSD NixOS
# configurations and creates zones for all definitions of networking.extraHosts
# (except those that point to 127.0.0.1 or ::1) within the current test network
# and delegates these zones using a fake root zone served by a BIND recursive
# name server.
{ config, nodes, pkgs, lib, ... }:

{
  options.test-support.resolver.enable = lib.mkOption {
    type = lib.types.bool;
    default = true;
    internal = true;
    description = ''
      Whether to enable the resolver that automatically discovers zone in the
      test network.

      This option is <literal>true</literal> by default, because the module
      defining this option needs to be explicitly imported.

      The reason this option exists is for the
      <filename>nixos/tests/common/letsencrypt</filename> module, which
      needs that option to disable the resolver once the user has set its own
      resolver.
    '';
  };

  config = lib.mkIf config.test-support.resolver.enable {
    networking.firewall.enable = false;
    services.bind.enable = true;
    services.bind.cacheNetworks = lib.mkForce [ "any" ];
    services.bind.forwarders = lib.mkForce [];
    services.bind.zones = lib.singleton {
      name = ".";
      file = let
        addDot = zone: zone + lib.optionalString (!lib.hasSuffix "." zone) ".";
        mkNsdZoneNames = zones: map addDot (lib.attrNames zones);
        mkBindZoneNames = zones: map (zone: addDot zone.name) zones;
        getZones = cfg: mkNsdZoneNames cfg.services.nsd.zones
                     ++ mkBindZoneNames cfg.services.bind.zones;

        getZonesForNode = attrs: {
          ip = attrs.config.networking.primaryIPAddress;
          zones = lib.filter (zone: zone != ".") (getZones attrs.config);
        };

        zoneInfo = lib.mapAttrsToList (lib.const getZonesForNode) nodes;

        # A and AAAA resource records for all the definitions of
        # networking.extraHosts except those for 127.0.0.1 or ::1.
        #
        # The result is an attribute set with keys being the host name and the
        # values are either { ipv4 = ADDR; } or { ipv6 = ADDR; } where ADDR is
        # the IP address for the corresponding key.
        recordsFromExtraHosts = let
          getHostsForNode = lib.const (n: n.config.networking.extraHosts);
          allHostsList = lib.mapAttrsToList getHostsForNode nodes;
          allHosts = lib.concatStringsSep "\n" allHostsList;

          reIp = "[a-fA-F0-9.:]+";
          reHost = "[a-zA-Z0-9.-]+";

          matchAliases = str: let
            matched = builtins.match "[ \t]+(${reHost})(.*)" str;
            continue = lib.singleton (lib.head matched)
                    ++ matchAliases (lib.last matched);
          in if matched == null then [] else continue;

          matchLine = str: let
            result = builtins.match "[ \t]*(${reIp})[ \t]+(${reHost})(.*)" str;
          in if result == null then null else {
            ipAddr = lib.head result;
            hosts = lib.singleton (lib.elemAt result 1)
                 ++ matchAliases (lib.last result);
          };

          skipLine = str: let
            rest = builtins.match "[^\n]*\n(.*)" str;
          in if rest == null then "" else lib.head rest;

          getEntries = str: acc: let
            result = matchLine str;
            next = getEntries (skipLine str);
            newEntry = acc ++ lib.singleton result;
            continue = if result == null then next acc else next newEntry;
          in if str == "" then acc else continue;

          isIPv6 = str: builtins.match ".*:.*" str != null;
          loopbackIps = [ "127.0.0.1" "::1" ];
          filterLoopback = lib.filter (e: !lib.elem e.ipAddr loopbackIps);

          allEntries = lib.concatMap (entry: map (host: {
            inherit host;
            ${if isIPv6 entry.ipAddr then "ipv6" else "ipv4"} = entry.ipAddr;
          }) entry.hosts) (filterLoopback (getEntries (allHosts + "\n") []));

          mkRecords = entry: let
            records = lib.optional (entry ? ipv6) "AAAA ${entry.ipv6}"
                   ++ lib.optional (entry ? ipv4) "A ${entry.ipv4}";
            mkRecord = typeAndData: "${entry.host}. IN ${typeAndData}";
          in lib.concatMapStringsSep "\n" mkRecord records;

        in lib.concatMapStringsSep "\n" mkRecords allEntries;

        # All of the zones that are subdomains of existing zones.
        # For example if there is only "example.com" the following zones would
        # be 'subZones':
        #
        #  * foo.example.com.
        #  * bar.example.com.
        #
        # While the following would *not* be 'subZones':
        #
        #  * example.com.
        #  * com.
        #
        subZones = let
          allZones = lib.concatMap (zi: zi.zones) zoneInfo;
          isSubZoneOf = z1: z2: lib.hasSuffix z2 z1 && z1 != z2;
        in lib.filter (z: lib.any (isSubZoneOf z) allZones) allZones;

        # All the zones without 'subZones'.
        filteredZoneInfo = map (zi: zi // {
          zones = lib.filter (x: !lib.elem x subZones) zi.zones;
        }) zoneInfo;

      in pkgs.writeText "fake-root.zone" ''
        $TTL 3600
        . IN SOA ns.fakedns. admin.fakedns. ( 1 3h 1h 1w 1d )
        ns.fakedns. IN A ${config.networking.primaryIPAddress}
        . IN NS ns.fakedns.
        ${lib.concatImapStrings (num: { ip, zones }: ''
          ns${toString num}.fakedns. IN A ${ip}
          ${lib.concatMapStrings (zone: ''
          ${zone} IN NS ns${toString num}.fakedns.
          '') zones}
        '') (lib.filter (zi: zi.zones != []) filteredZoneInfo)}
        ${recordsFromExtraHosts}
      '';
    };
  };
}