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

with lib;

let
  cfg = config.services.minecraft-servers;

  eulaFile = builtins.toFile "eula.txt" ''
    # eula.txt managed by NixOS Configuration
    eula=true
  '';

  whitelistFile = server:
    pkgs.writeText "whitelist.json" (builtins.toJSON (mapAttrsToList (n: v: {
      name = n;
      uuid = v;
    }) server.whitelist));

  cfgToString = v: if builtins.isBool v then boolToString v else toString v;

  serverPropertiesFile = server:
    pkgs.writeText "server.properties" (''
      # server.properties managed by NixOS configuration
    '' + concatStringsSep "\n"
      (mapAttrsToList (n: v: "${n}=${cfgToString v}") server.serverProperties));

  tmux = "${getBin pkgs.tmux}/bin/tmux";

  stopScript = name:
    pkgs.writeScript "minecraft-stop" ''
      #!${pkgs.runtimeShell}

      if ! [ -d "/proc/$1" ]; then
        exit 0
      fi

      ${tmux} -S ${cfgdataDir}/${name}.sock send-keys Enter stop Enter
      ${getBin pkgs.coreutils}/bin/tail --pid-"$1" -f /dev/null
    '';

  cfgdataDir = "/var/lib/minecraft";

  mkService = name: inst:
    builtins.trace "${name} building" {
      name = "minecraft-server-${name}";
      value = builtins.trace "${name}: value: build" {
        description = "Minecraft Server Service: ${name}";
        wantedBy = [ "multi-user.target" ];
        after = [ "network.target" ];

        serviceConfig =
          builtins.trace "${name}: value: serviceConfig: building" {
            ExecStart = ''
                    ${tmux} -S ${cfgdataDir}/${name}.sock new \
                      -d ${inst.package}/bin/minecraft-server ${inst.jvmOpts}
              #     '';
            ExecStop = "${stopScript name} $MAINPID";
            Restart = "always";
            Type = "forking";
            GuessMainPIP = true;
            User = "minecraft";
            WorkingDirectory = "${cfgdataDir}/${name}";
          };

        preStart = ''
          ln -sf ${eulaFile} eula.txt
        '' + (if inst.declarative then ''
          if [ -e .declarative ]; then
            # Was declarative before, no need to back up anything
            ln -sf ${whitelistFile inst} whitelist.json
            cp -f ${serverPropertiesFile inst} server.properties
          else
            # Declarative for the first time, backup stateful files
            ln -sb --suffix=.stateful ${whitelistFile inst} whitelist.json
            cp -b --suffix=.stateful ${
              serverPropertiesFile inst
            } server.properties
            # server.properties must have write permissions, because every time
            # the server starts it first parses the file and then regenerates it..
            chmod +w server.properties
            echo "Autogenerated file that signifies that this server configuration is managed declaratively by NixOS" \
              > .declarative
          fi
        '' else ''
          if [ -e .declarative ]; then
            rm .declarative
          fi
        '');

        postStart = ''
          ${pkgs.coreutils}/bin/chmod 660 ${cfgdataDir}/${name}.sock
          ${pkgs.coreutils}/bin/chgrp minecraft ${cfgdataDir}/${name}.sock
        '';
      };
    };

  generatedServices = mapAttrs' mkService cfg.servers;

in {
  options = {
    services.minecraft-servers = {
      enable = mkEnableOption "minecraft servers";
      # TODO: verbose minecraft-servers enable option

      openFirewall =
        mkEnableOption "opening the firewall for each server by default";
      # TODO: verbose outer openFirewall option

      dataDir = mkOption {
        type = types.path;
        default = "/var/lib/minecraft";
        # TODO: verbose dataDir option
      };

      servers = mkOption {
        type = types.attrsOf (types.submodule {
          enable = mkEnableOption "this minecraft server";
          # TODO: verbose server enable option

          declarative = mkEnableOption "declarative server management";
          # TODO: verbose declarative option

          eula = mkEnableOption "accepting the eula";
          # TODO: verbose eula option

          openFirewall = mkOption {
            type = types.bool;
            default = true; # cfg.openFirewall;
            # TODO: openFirewall description
          };

          jvmOpts = mkOption {
            type = types.separatedString " ";
            default = "-Xmx2048M -Xms2048M";
            # TODO: verbose jvmOpts option
          };

          package = mkOption {
            type = types.package;
            default = pkgs.minecraft-server;
            # TODO: verbose package option
          };

          whitelist = mkOption {
            type = let
              minecraftUUID = types.strMatching
                "[0-9a-f]{8}-[0-9a-f]{4}-[0-9a-f]{4}-[0-9a-f]{4}-[0-9a-f]{12}"
                // {
                  description = "Minecraft UUID";
                };
            in types.attrsOf minecraftUUID;
            default = { };
            # TODO: verbose whitelist option
          };

          serverProperties = mkOption {
            type = with types; attrsOf (oneOf [ bool int str ]);
            default = { server-port = 25565; };
            # TODO: verbose serverProperties option
          };
        });
      };
    };
  };

  config = mkIf cfg.enable {
    users.users.minecraft = {
      description = "Minecraft server service user";
      home = cfg.dataDir;
      createHome = true;
      isSystemUser = true;
      group = "minecraft";
    };

    users.groups.minecraft = { };

    systemd.services =
      mkIf (cfg.enable && cfg.servers != { }) generatedServices;

  };

  # networking.firewall = let

  #   propertyFunc = attrsets.mapAttrsToList (name: value:
  #     let props = value.serverProperties;
  #     in (if value.declarative then [
  #       (props.server-port or 25565)
  #       (if props.enable-rcon or false then
  #         props."rcon.port" or 25575
  #       else
  #         null)
  #       (if props.enable-query or false then
  #         props "query.port" or 25565
  #       else
  #         null)
  #     ] else
  #       null)) cfg.servers;

  #   openedPorts = lists.flatten [ serverPorts queryPorts rconPorts ];
  # in {
  #   allowedUDPPorts = openedPorts;
  #   allowedTCPPorts = openedPorts;
  # };

  # assertions = [{
  #   assertion = all (i: i.eula == true) (attrValues cfg.servers);
  #   message = "You must agree to Mojangs EULA to run minecraft-server."
  #     + " Read https://account.mojang.com/documents/minecraft_eula and"
  #     + " set `services.minecraft-servers.servers.<name>.eula` to `true` for all servers if you agree.";
  # }];
}