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

with lib;

let
  cfg = config.services.zerotierone;
in
{
  options.services.zerotierone.enable = mkEnableOption (lib.mdDoc "ZeroTierOne");

  options.services.zerotierone.joinNetworks = mkOption {
    default = [];
    example = [ "a8a2c3c10c1a68de" ];
    type = types.listOf types.str;
    description = lib.mdDoc ''
      List of ZeroTier Network IDs to join on startup.
      Note that networks are only ever joined, but not automatically left after removing them from the list.
      To remove networks, use the ZeroTier CLI: `zerotier-cli leave <network-id>`
    '';
  };

  options.services.zerotierone.port = mkOption {
    default = 9993;
    type = types.port;
    description = lib.mdDoc ''
      Network port used by ZeroTier.
    '';
  };

  options.services.zerotierone.package = mkOption {
    default = pkgs.zerotierone;
    defaultText = literalExpression "pkgs.zerotierone";
    type = types.package;
    description = lib.mdDoc ''
      ZeroTier One package to use.
    '';
  };

  config = mkIf cfg.enable {
    systemd.services.zerotierone = {
      description = "ZeroTierOne";

      wantedBy = [ "multi-user.target" ];
      after = [ "network.target" ];
      wants = [ "network-online.target" ];

      path = [ cfg.package ];

      preStart = ''
        mkdir -p /var/lib/zerotier-one/networks.d
        chmod 700 /var/lib/zerotier-one
        chown -R root:root /var/lib/zerotier-one
      '' + (concatMapStrings (netId: ''
        touch "/var/lib/zerotier-one/networks.d/${netId}.conf"
      '') cfg.joinNetworks);
      serviceConfig = {
        ExecStart = "${cfg.package}/bin/zerotier-one -p${toString cfg.port}";
        Restart = "always";
        KillMode = "process";
        TimeoutStopSec = 5;
      };
    };

    # ZeroTier does not issue DHCP leases, but some strangers might...
    networking.dhcpcd.denyInterfaces = [ "zt*" ];

    # ZeroTier receives UDP transmissions
    networking.firewall.allowedUDPPorts = [ cfg.port ];

    environment.systemPackages = [ cfg.package ];

    # Prevent systemd from potentially changing the MAC address
    systemd.network.links."50-zerotier" = {
      matchConfig = {
        OriginalName = "zt*";
      };
      linkConfig = {
        AutoNegotiation = false;
        MACAddressPolicy = "none";
      };
    };
  };
}