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

let
  cfg = config.local.services.vpn.wireguard;

  addrsViaDefaultInterface = [
    # cache.nixos.org
    "151.101.86.217/32"
    "146.75.118.217/32"
    # tbank.ru
    "178.248.236.218/32"
  ];
in
{
  options.local.services.vpn.wireguard = with lib; {
    enable = mkEnableOption "Enable wireguard vpn";
    ip = mkOption {
      type = types.str;
      example = "10.100.0.1/24";
    };
    privateKeyFile = mkOption {
      type = types.str;
    };
    server = {
      addr = mkOption {
        type = types.str;
      };
      port = mkOption {
        type = types.int;
      };
      publicKey = mkOption {
        type = types.str;
      };
    };
  };

  config = lib.mkIf cfg.enable {
    networking.firewall = {
      allowedUDPPorts = [ cfg.server.port ]; # Clients and peers can use the same port, see listenport
    };
    # Enable WireGuard
    networking.wg-quick.interfaces = {
      # "wg0" is the network interface name. You can name the interface arbitrarily.
      wg0 = {
        # Determines the IP address and subnet of the client's end of the tunnel interface.
        address = [ cfg.ip ];
        dns = [ "10.20.30.1" ];

        listenPort = cfg.server.port; # to match firewall allowedUDPPorts (without this wg uses random port numbers)

        # Path to the private key file.
        privateKeyFile = cfg.privateKeyFile;

        postUp = ''
          addr=`${pkgs.iproute2}/bin/ip route | ${pkgs.gawk}/bin/awk '/default/ {print $3; exit}'`
          interface=`${pkgs.iproute2}/bin/ip route | ${pkgs.gawk}/bin/awk '/default/ {print $5; exit}'`
        '' + lib.concatLines (map
          (addr: "${pkgs.iproute2}/bin/ip route add ${addr} via $addr dev $interface || true")
          addrsViaDefaultInterface
        );

        preDown = ''
          addr=`${pkgs.iproute2}/bin/ip route | ${pkgs.gawk}/bin/awk '/default/ {print $3; exit}'`
          interface=`${pkgs.iproute2}/bin/ip route | ${pkgs.gawk}/bin/awk '/default/ {print $5; exit}'`
        '' + lib.concatLines (map
          (addr: "${pkgs.iproute2}/bin/ip route del ${addr} via $addr dev $interface || true")
          addrsViaDefaultInterface
        );

        peers = [
          # For a client configuration, one peer entry for the server will suffice.

          {
            # Public key of the server (not a file path).
            publicKey = cfg.server.publicKey;

            # Forward all the traffic via VPN.
            allowedIPs = [ "0.0.0.0/0" ];
            # Or forward only particular subnets
            # allowedIPs = [ "192.168.0.0/24" ];

            # Set this to the server IP and port.
            endpoint = "${cfg.server.addr}:${toString cfg.server.port}";

            # Send keepalives every 25 seconds. Important to keep NAT tables alive.
            persistentKeepalive = 15;
          }
        ];
      };
    };
  };
}