config/lib/mkSystem.nix

# This function creates a NixOS system based on our VM setup for a
# particular architecture.
{
  nixpkgs,
  overlays,
  inputs,
  mkNeovim,
}:
name:
{
  user, # ./users/{name}
  host, # ./users/{name}/{host} (optional)
  system, # arch-os
  extraModules ? [ ],
}:
let
  darwin = nixpkgs.lib.strings.hasSuffix "-darwin" system;
  getInputModule = a: b: inputs.${a}.${if darwin then "darwinModules" else "nixosModules"}.${b};

  # NixOS vs nix-darwin functions
  systemFunc = if darwin then inputs.darwin.lib.darwinSystem else nixpkgs.lib.nixosSystem;

  userDir = ../users + "/${user}";
  userConfig = import (userDir + "/user.nix");
  hostDir = userDir + "/${host}";

  hostConfigPath = hostDir + "/configuration.nix";
  userConfigPath = userDir + "/configuration.nix";
  hostHomePath = hostDir + "/home.nix";
  userHomePath = userDir + "/home.nix";

  pathOrNull = a: if builtins.pathExists a then a else null;

  # Arguments passed to all module files
  args = {
    inherit inputs;
    currentSystem = system;
    # Details about the host machine
    host = {
      inherit darwin name;
      linux = !darwin;
    };
    user =
      (
        {
          # This acts as formal documentation for what is allowed in user.nix
          username, # unix username
          name, # your display name
          email, # for identity in programs such as git
          dotfilesDir, # location to `../.`
          timeZone ? "America/Los_Angeles",
          # Stylix/Theming
          theme ? null, # theme name for stylix
          sexuality ? null, # pride flag for hyfetch
          font ? null, # font to use
          term, # preferred $TERM
          editor, # preferred $EDITOR
          browser ? null, # preferred $BROWSER
        }@user:
        user
      )
        userConfig;
  };
  systemSettings = rec {
    inherit darwin;
    homeDir = "/${if darwin then "Users" else "home"}/${userConfig.username}";
  };

  mainHomeImports = builtins.filter (f: f != null) [
    (pathOrNull userHomePath)
    (pathOrNull hostHomePath)
    {
      home.packages = [
        (mkNeovim user system)
      ];
    }
  ];
in
systemFunc {
  inherit system;

  modules =
    builtins.filter (f: f != null) [
      # Apply our overlays. Overlays are keyed by system type so we have
      # to go through and apply our system type. We do this first so
      # the overlays are available globally.
      { nixpkgs.overlays = overlays; }

      # Modules shared between nix-darwin and NixOS
      ../modules/shared
      # Modules for the specific OS
      (if darwin then ../modules/macos else ../modules/nixos)

      # The user-wide configuration.nix
      (pathOrNull userConfigPath)
      # The host-wide configuration.nix
      (pathOrNull hostConfigPath)

      # Set up nix-index and enable comma for easy one-shot command use
      # https://github.com/nix-community/comma
      (getInputModule "nix-index-database" "nix-index")
      { programs.nix-index-database.comma.enable = true; }

      # Themes for all programs
      (getInputModule "stylix" "stylix")

      # Home manager
      (getInputModule "home-manager" "home-manager")
      {
        home-manager = {
          useGlobalPkgs = true;
          useUserPackages = true;
          backupFileExtension = "hm-backup";
          # Arguments passed to all module files
          extraSpecialArgs = args // {
            inherit mainHomeImports;
          };
          # can't find how to make this an array without the param
          users.${userConfig.username} = ../modules/home;
        };
        users.users.${userConfig.username}.home = systemSettings.homeDir;
      }

      # Arguments passed to all module files
      { config._module.args = args; }
    ]
    # Add extra modules specified from config
    ++ extraModules;
}