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

with lib;

let
  inherit (lib.types) attrsOf coercedTo listOf oneOf str int bool;
  cfg = config.services.smartdns;

  confFile = pkgs.writeText "smartdns.conf" (with generators;
    toKeyValue {
      mkKeyValue = mkKeyValueDefault {
        mkValueString = v:
          if isBool v then
            if v then "yes" else "no"
          else
            mkValueStringDefault { } v;
      } " ";
      listsAsDuplicateKeys =
        true; # Allowing duplications because we need to deal with multiple entries with the same key.
    } cfg.settings);
in {
  options.services.smartdns = {
    enable = mkEnableOption (lib.mdDoc "SmartDNS DNS server");

    bindPort = mkOption {
      type = types.port;
      default = 53;
      description = lib.mdDoc "DNS listening port number.";
    };

    settings = mkOption {
      type =
      let atom = oneOf [ str int bool ];
      in attrsOf (coercedTo atom toList (listOf atom));
      example = literalExpression ''
        {
          bind = ":5353 -no-rule -group example";
          cache-size = 4096;
          server-tls = [ "8.8.8.8:853" "1.1.1.1:853" ];
          server-https = "https://cloudflare-dns.com/dns-query -exclude-default-group";
          prefetch-domain = true;
          speed-check-mode = "ping,tcp:80";
        };
      '';
      description = lib.mdDoc ''
        A set that will be generated into configuration file, see the [SmartDNS README](https://github.com/pymumu/smartdns/blob/master/ReadMe_en.md#configuration-parameter) for details of configuration parameters.
        You could override the options here like {option}`services.smartdns.bindPort` by writing `settings.bind = ":5353 -no-rule -group example";`.
      '';
    };
  };

  config = lib.mkIf cfg.enable {
    services.smartdns.settings.bind = mkDefault ":${toString cfg.bindPort}";

    systemd.packages = [ pkgs.smartdns ];
    systemd.services.smartdns.wantedBy = [ "multi-user.target" ];
    systemd.services.smartdns.restartTriggers = [ confFile ];
    environment.etc."smartdns/smartdns.conf".source = confFile;
    environment.etc."default/smartdns".source =
      "${pkgs.smartdns}/etc/default/smartdns";
  };
}