dotfiles.nix/modules/nix.nix

# https://github.com/LnL7/nix-darwin/issues/277#issuecomment-992866471

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

with lib;

let
  cfg = config.nix;

  nixRegistry = builtins.mapAttrs (name: value: { flake = value; }) inputs;
  etcNixInputs = pkgs.runCommandNoCC "etc-nix-inputs"
    {
      inputNames = builtins.attrNames inputs;
      inputPaths = builtins.map (x: x.outPath) (builtins.attrValues inputs);
    } ''
    mkdir -p $out
    inputNames=($inputNames)
    inputPaths=($inputPaths)
    for (( i=0; i<''${#inputNames[@]}; i++)); do
      source=''${inputPaths[$i]}
      name=''${inputNames[$i]}
      if [[ -f $source/default.nix ]]; then
        ln -s $source $out/$name
      fi
    done
  '';
in

# Based on flake-utils-plus#nixosModules.autoGenFromInputs
  # https://github.com/gytis-ivaskevicius/flake-utils-plus/blob/master/lib/options.nix
  #
  # We're not using that directly because we don't need the rest of the flake, and to work around
  # https://github.com/gytis-ivaskevicius/flake-utils-plus/issues/105 and
  # https://github.com/gytis-ivaskevicius/flake-utils-plus/issues/107

{
  options = {
    nix.generateNixPathFromInputs = mkOption {
      type = types.bool;
      description = ''
        If set, NIX_PATH will be generated from available inputs.
        This requires `nix.linkInputs` to be enabled, and setting this will default
        `nix.linkInputs` to true.
      '';
      default = false;
      example = true;
    };
    nix.generateRegistryFromInputs = mkOption {
      type = types.bool;
      description = ''
        If set, the system Nix registry will be generated from available inputs.
        Otherwise, the registry will still include the `self` flake.
      '';
      default = false;
      example = true;
    };
    nix.linkInputs = mkOption {
      type = types.bool;
      description = "If set, inputs will be symlinked into /etc/nix/inputs.";
      example = true;
    };
  };

  config = {
    assertions = [{
      assertion = cfg.generateNixPathFromInputs -> cfg.linkInputs;
      message = "nix.generateNixPathFromInputs requires nix.linkInputs";
    }];

    nix.linkInputs = mkDefault cfg.generateNixPathFromInputs;

    nix.registry =
      if cfg.generateRegistryFromInputs
      then nixRegistry
      else { self.flake = inputs.self; };

    environment.etc."nix/inputs" = mkIf cfg.linkInputs {
      source = etcNixInputs;
    };

    nix.nixPath = mkIf cfg.generateNixPathFromInputs [ "/etc/nix/inputs" ];
  };
}