{
  lib,
  config,
  ...
}:
let
  inherit (import ./constants.nix) targetMachines pathToRoot;
  escapedJson = v: lib.replaceStrings [ "\"" ] [ "\\\\\"" ] (lib.strings.toJSON v);
in
{
  _class = "nixosTest";
  name = "deployment-model";
  sourceFileset = lib.fileset.unions [
    ../../data-model.nix
    ../../function.nix
    ./constants.nix
    ./deployment.nix
  ];

  nodes.deployer =
    { pkgs, ... }:
    {
      environment.systemPackages = with pkgs; [
        jq
      ];
      system.extraDependenciesFromModule =
        { pkgs, ... }:
        {
          environment.systemPackages = with pkgs; [
            hello
          ];
        };
    };

  extraTestScript = ''
    ${lib.concatStringsSep "\n" (
      lib.lists.map (nodeName: ''
        with subtest("Check the status before deployment"):
          ${nodeName}.fail("${nodeName} 1>&2")

        with subtest("Run the deployment for ${nodeName}"):
          deployer.succeed("""
            set -euo pipefail

            # INSTANTIATE
            command=(nix-instantiate --expr '
              import ${pathToRoot}/deployment/nixos.nix {
                configuration = import ${pathToRoot}/deployment/check/data-model/deployment.nix {
                  config = builtins.fromJSON "${
                    escapedJson {
                      inherit (config) enableAcme;
                      acmeNodeIP = if config.enableAcme then config.nodes.acme.networking.primaryIPAddress else null;
                    }
                  }";
                };
              }
            ')
            # DEPLOY
            host="root@${nodeName}"
            sshOpts=(
              -o StrictHostKeyChecking=no
              -o "ConnectTimeout=1"
              -o "ServerAliveInterval=1"
            )
            # instantiate the config in /nix/store
            "''${command[@]}" -A out_path
            # get the realized derivation to deploy
            outPath=$(nix-store --realize "$("''${command[@]}" --eval --strict --json | jq -r '.drv_path')")
            # deploy the config by nix-copy-closure
            NIX_SSHOPTS="''${sshOpts[*]}" nix-copy-closure --to "$host" "$outPath" --gzip --use-substitutes
            # switch the remote host to the config
            output=$(ssh "''${sshOpts[@]}" "$host" "nix-env --profile /nix/var/nix/profiles/system --set $outPath; nohup $outPath/bin/switch-to-configuration switch &" 2>&1) || echo "status code: $?"
            echo "output: $output"
            if [[ $output != *"Timeout, server ${nodeName} not responding"* ]]; then
              echo "non-timeout error: $output"
              exit 1
            else
              exit 0
            fi
          """)
          ${nodeName}.wait_for_unit("multi-user.target")
          ${nodeName}.succeed("${nodeName} 1>&2")
      '') targetMachines
    )}
  '';
}