{ pkgs, serverPkg, clientPkg }:
{
  name = "lightscale-lab-netem";
  nodes = {
    node1 = { ... }: {
      networking.hostName = "node1";
      networking.usePredictableInterfaceNames = false;
      virtualisation.vlans = [ 1 ];
      networking.interfaces.eth1.useDHCP = false;
      networking.interfaces.eth1.ipv4.addresses = [
        { address = "10.0.0.1"; prefixLength = 24; }
      ];
      networking.firewall.enable = false;
      boot.kernelModules = [ "wireguard" ];
      environment.systemPackages = [
        serverPkg
        clientPkg
        pkgs.wireguard-tools
        pkgs.iproute2
        pkgs.iputils
        pkgs.netcat-openbsd
        pkgs.curl
      ];
    };

    natgw = { ... }: {
      networking.hostName = "natgw";
      networking.usePredictableInterfaceNames = false;
      virtualisation.vlans = [ 1 2 ];
      networking.interfaces.eth1.useDHCP = false;
      networking.interfaces.eth1.ipv4.addresses = [
        { address = "10.0.0.2"; prefixLength = 24; }
      ];
      networking.interfaces.eth2.useDHCP = false;
      networking.interfaces.eth2.ipv4.addresses = [
        { address = "192.168.50.1"; prefixLength = 24; }
      ];
      networking.firewall.enable = false;
      boot.kernel.sysctl."net.ipv4.ip_forward" = 1;
      environment.systemPackages = [
        pkgs.iproute2
        pkgs.iputils
        pkgs.iptables
        pkgs.conntrack-tools
      ];
    };

    node3 = { ... }: {
      networking.hostName = "node3";
      networking.usePredictableInterfaceNames = false;
      virtualisation.vlans = [ 2 ];
      networking.interfaces.eth1.useDHCP = false;
      networking.interfaces.eth1.ipv4.addresses = [
        { address = "192.168.50.10"; prefixLength = 24; }
      ];
      networking.defaultGateway = {
        address = "192.168.50.1";
        interface = "eth1";
      };
      networking.firewall.enable = false;
      boot.kernelModules = [ "wireguard" ];
      environment.systemPackages = [
        clientPkg
        pkgs.wireguard-tools
        pkgs.iproute2
        pkgs.iputils
        pkgs.curl
      ];
    };
  };

  testScript = ''
    start_all()
    node1.wait_for_unit("multi-user.target")
    natgw.wait_for_unit("multi-user.target")
    node3.wait_for_unit("multi-user.target")

    node1.wait_until_succeeds("ip -4 addr show dev eth1 | grep -q '10.0.0.1/24'")
    natgw.wait_until_succeeds("ip -4 addr show dev eth1 | grep -q '10.0.0.2/24'")
    natgw.wait_until_succeeds("ip -4 addr show dev eth2 | grep -q '192.168.50.1/24'")
    node3.wait_until_succeeds("ip -4 addr show dev eth1 | grep -q '192.168.50.10/24'")
    node3.wait_until_succeeds("ip -4 route show default | grep -q 'via 192.168.50.1'")

    natgw.succeed("iptables -P FORWARD ACCEPT")
    natgw.succeed("iptables -F")
    natgw.succeed("iptables -t nat -F")

    def set_nat_port(port):
        natgw.succeed("iptables -t nat -F")
        natgw.succeed(
            f"iptables -t nat -A PREROUTING -i eth1 -p udp --dport {port} "
            "-j DNAT --to-destination 192.168.50.10:51820"
        )
        natgw.succeed(
            f"iptables -t nat -A POSTROUTING -o eth1 -p udp -s 192.168.50.10 "
            f"--sport 51820 -j SNAT --to-source 10.0.0.2:{port}"
        )
        natgw.succeed("iptables -t nat -A POSTROUTING -o eth1 -j MASQUERADE")
        natgw.execute("conntrack -F || true")

    set_nat_port(40000)

    node1.succeed("touch /tmp/lightscale-server.log")
    node1.execute("sh -c 'tail -n +1 -f /tmp/lightscale-server.log >/dev/console 2>&1 &'")
    node1.succeed(
        "systemd-run --no-block --unit=lightscale-server --service-type=simple "
        "--property=Restart=on-failure --property=RestartSec=1 "
        "--property=TimeoutStartSec=30 "
        "--property=StandardOutput=append:/tmp/lightscale-server.log "
        "--property=StandardError=append:/tmp/lightscale-server.log "
        "--setenv=RUST_LOG=info --setenv=LIGHTSCALE_ADMIN_TOKEN=test-admin -- "
        "lightscale-server --listen 10.0.0.1:8080 --state /tmp/lightscale-state.json"
    )
    node1.wait_for_unit("lightscale-server.service")
    node1.wait_for_open_port(8080, addr="10.0.0.1", timeout=120)

    import json

    net = json.loads(node1.succeed(
        "curl -sSf -X POST http://10.0.0.1:8080/v1/networks "
        "-H 'authorization: Bearer test-admin' "
        "-H 'content-type: application/json' "
        "-d '{\"name\":\"netem\",\"bootstrap_token_ttl_seconds\":600,"
        "\"bootstrap_token_uses\":10,\"bootstrap_token_tags\":[\"netem\"]}'"
    ))
    token = net["bootstrap_token"]["token"]

    def enroll(node, name, endpoints):
        node.succeed(
            "lightscale-client --profile netem --config /tmp/ls-config.json "
            "init http://10.0.0.1:8080"
        )
        node.succeed(
            f"lightscale-client --profile netem --config /tmp/ls-config.json "
            f"--state-dir /tmp/ls-state register --node-name {name} -- {token}"
        )
        cmd = (
            "lightscale-client --profile netem --config /tmp/ls-config.json "
            "--state-dir /tmp/ls-state heartbeat"
        )
        for endpoint in endpoints:
            cmd += f" --endpoint {endpoint}"
        node.succeed(cmd)

    enroll(node1, "node1", ["10.0.0.1:51820"])
    enroll(node3, "node3", ["10.0.0.2:40000", "10.0.0.2:41000"])

    def start_agent(node, endpoints):
        node.succeed("touch /tmp/lightscale-agent.log")
        cmd = (
            "lightscale-client --profile netem --config /tmp/ls-config.json "
            "--state-dir /tmp/ls-state agent --listen-port 51820 "
            "--heartbeat-interval 5 --longpoll-timeout 5 "
            "--endpoint-stale-after 5 --endpoint-max-rotations 2"
        )
        for endpoint in endpoints:
            cmd += f" --endpoint {endpoint}"
        node.succeed(
            "systemd-run --no-block --unit=lightscale-agent --service-type=simple "
            "--property=Restart=on-failure --property=RestartSec=1 "
            "--property=TimeoutStartSec=30 "
            "--property=StandardOutput=append:/tmp/lightscale-agent.log "
            "--property=StandardError=append:/tmp/lightscale-agent.log -- "
            + cmd
        )
        node.wait_for_unit("lightscale-agent.service")
        node.wait_until_succeeds("ip link show ls-netem", timeout=60)

    start_agent(node1, ["10.0.0.1:51820"])
    start_agent(node3, ["10.0.0.2:40000", "10.0.0.2:41000"])

    data1 = json.loads(node1.succeed("cat /tmp/ls-state/state.json"))
    data3 = json.loads(node3.succeed("cat /tmp/ls-state/state.json"))
    node1_ip = data1["ipv4"]
    node3_ip = data3["ipv4"]

    node1.wait_until_succeeds(f"ping -c 3 {node3_ip}", timeout=180)
    node3.wait_until_succeeds(f"ping -c 3 {node1_ip}", timeout=180)

    # Impair WAN path between node1 and natgw to validate behavior under delay/loss.
    natgw.succeed("tc qdisc replace dev eth1 root netem delay 120ms 20ms loss 8%")
    natgw.succeed("tc -s qdisc show dev eth1 | grep -q netem")

    def eventually_ping(src, dst):
        src.wait_until_succeeds(
            f"for i in $(seq 1 20); do ping -c 1 -W 1 {dst} && exit 0; sleep 1; done; exit 1",
            timeout=180,
        )

    eventually_ping(node1, node3_ip)
    eventually_ping(node3, node1_ip)

    natgw.succeed("tc qdisc del dev eth1 root")

    # Simulate NAT rebinding by changing external UDP port for node3.
    set_nat_port(41000)

    node1.wait_until_succeeds("wg show ls-netem endpoints | grep -q ':41000'", timeout=180)
    node1.wait_until_succeeds(f"ping -c 3 {node3_ip}", timeout=180)
    node3.wait_until_succeeds(f"ping -c 3 {node1_ip}", timeout=180)
  '';
}