nichts/modules/system/nix/determinate.mod.nix

{
  config,
  lib,
  pkgs,
  sources,
  ...
}:
let
  determinate = (import sources.flake-compat { src = sources.determinate; }).outputs;
  dix =
    (import sources.flake-compat { src = determinate.inputs.nix; })
    .outputs.packages.${pkgs.stdenv.system}.nix;

  # Stronger than mkDefault (1000), weaker than mkForce (50) and the "default override priority"
  # (100).
  mkPreferable = lib.mkOverride 750;

  # Stronger than the "default override priority", as the upstream module uses that, and weaker than mkForce (50).
  mkMorePreferable = lib.mkOverride 75;
in
{
  config = {
    nix = {
      package = dix;
    };
    environment.systemPackages = [
      determinate.packages.${pkgs.stdenv.system}.default
    ];

    # NOTE(cole-h): Move the generated nix.conf to /etc/nix/nix.custom.conf, which is included from
    # the Determinate Nixd-managed /etc/nix/nix.conf.
    environment.etc."nix/nix.conf".target = "nix/nix.custom.conf";
    systemd = {
      services.nix-daemon.serviceConfig = {
        ExecStart = [
          ""
          "@${
            determinate.packages.${pkgs.stdenv.system}.default
          }/bin/determinate-nixd determinate-nixd --nix-bin ${config.nix.package}/bin daemon"
        ];
        KillMode = mkPreferable "process";
        LimitNOFILE = mkMorePreferable 1048576;
        LimitSTACK = mkPreferable "64M";
        TasksMax = mkPreferable 1048576;
      };
      sockets = {
        nix-daemon.socketConfig.FileDescriptorName = "nix-daemon.socket";
        determinate-nixd = {
          description = "Determinate Nixd Daemon Socket";
          wantedBy = [ "sockets.target" ];
          before = [ "multi-user.target" ];

          unitConfig = {
            RequiresMountsFor = [
              "/nix/store"
              "/nix/var/determinate"
            ];
          };

          socketConfig = {
            Service = "nix-daemon.service";
            FileDescriptorName = "determinate-nixd.socket";
            ListenStream = "/nix/var/determinate/determinate-nixd.socket";
            DirectoryMode = "0755";
          };
        };
      };
    };
  };
}