{ nixpkgs, system, overlay }:

with import (nixpkgs + "/nixos/lib/testing-python.nix") {
  inherit system;
  extraConfigurations = [ { nixpkgs.overlays = [ overlay ]; } ];
};

let
  nix-fetch = pkgs.writeText "fetch.nix" ''
    derivation {
        # This derivation is an copy from what is available over at
        # nix.git:corepkgs/fetchurl.nix
        builder = "builtin:fetchurl";

        # We're going to fetch data from the http_dns instance created before
        # we expect the content to be the same as the content available there.
        # ```
        # $ nix-hash --type sha256 --to-base32 $(echo "hello world" | sha256sum | cut -d " " -f 1)
        # 0ix4jahrkll5zg01wandq78jw3ab30q4nscph67rniqg5x7r0j59
        # ```
        outputHash = "0ix4jahrkll5zg01wandq78jw3ab30q4nscph67rniqg5x7r0j59";
        outputHashAlgo = "sha256";
        outputHashMode = "flat";

        name = "example.com";
        url = "http://example.com";

        unpack = false;
        executable = false;

        system = "builtin";

        preferLocalBuild = true;

        impureEnvVars = [
            "http_proxy" "https_proxy" "ftp_proxy" "all_proxy" "no_proxy"
        ];

        urls = [ "http://example.com" ];
      }
  '';
in

makeTest (

rec {
  name = "nss-preload";

  nodes = {
    http_dns = { lib, pkgs, config, ... }: {
      networking.firewall.enable = false;
      networking.interfaces.eth1.ipv6.addresses = lib.mkForce [
        { address = "fd21::1"; prefixLength = 64; }
      ];
      networking.interfaces.eth1.ipv4.addresses = lib.mkForce [
        { address = "192.168.0.1"; prefixLength = 24; }
      ];

      services.unbound = {
        enable = true;
        enableRootTrustAnchor = false;
        settings = {
          server = {
            interface = [ "192.168.0.1" "fd21::1" "::1" "127.0.0.1" ];
            access-control = [ "192.168.0.0/24 allow" "fd21::/64 allow" "::1 allow" "127.0.0.0/8 allow" ];
            local-data = [
              ''"example.com. IN A 192.168.0.1"''
              ''"example.com. IN AAAA fd21::1"''
              ''"tarballs.nixos.org. IN A 192.168.0.1"''
              ''"tarballs.nixos.org. IN AAAA fd21::1"''
            ];
          };
        };
      };

      services.nginx = {
        enable = true;
        virtualHosts."example.com" = {
          root = pkgs.runCommand "testdir" {} ''
            mkdir "$out"
            echo hello world > "$out/index.html"
          '';
        };
      };
    };

    # client consumes a remote resolver
    client = { lib, nodes, pkgs, ... }: {
      networking.useDHCP = false;
      networking.nameservers = [
        (lib.head nodes.http_dns.config.networking.interfaces.eth1.ipv6.addresses).address
        (lib.head nodes.http_dns.config.networking.interfaces.eth1.ipv4.addresses).address
      ];
      networking.interfaces.eth1.ipv6.addresses = [
        { address = "fd21::10"; prefixLength = 64; }
      ];
      networking.interfaces.eth1.ipv4.addresses = [
        { address = "192.168.0.10"; prefixLength = 24; }
      ];

      nix.sandboxPaths = lib.mkForce [];
      nix.binaryCaches = lib.mkForce [];
      nix.useSandbox = lib.mkForce true;
    };
  };

  testScript = { nodes, ... }: ''
    http_dns.wait_for_unit("nginx")
    http_dns.wait_for_open_port(80)
    http_dns.wait_for_unit("unbound")
    http_dns.wait_for_open_port(53)

    client.start()
    client.wait_for_unit('multi-user.target')

    with subtest("can fetch data from a remote server outside sandbox"):
        client.succeed("nix --version >&2")
        client.succeed("curl -vvv http://example.com/index.html >&2")

    with subtest("nix-build can lookup dns and fetch data"):
        client.succeed("""
          nix-build ${nix-fetch} >&2
          """)
  '';
})