{
  description = "mat's nix configs";

  inputs = {
    # Package sets
    nixpkgs.url = "github:nixos/nixpkgs/nixpkgs-21.11-darwin";
    nixpkgs-unstable.url = github:NixOS/nixpkgs/nixpkgs-unstable;

    # Environment/system management
    darwin.url = "github:lnl7/nix-darwin/master";
    darwin.inputs.nixpkgs.follows = "nixpkgs-unstable";
    home-manager.url = "github:nix-community/home-manager";
    home-manager.inputs.nixpkgs.follows = "nixpkgs-unstable";

    # Other sources
    flake-compat = { url = github:edolstra/flake-compat; flake = false; };
    flake-utils.url = github:numtide/flake-utils;
  };

  outputs = { self, darwin, nixpkgs, home-manager, flake-utils, ... }@inputs:
    let

      inherit (darwin.lib) darwinSystem;
      inherit (inputs.nixpkgs-unstable.lib) attrValues makeOverridable optionalAttrs singleton;

      # Configuration for `nixpkgs`
      nixpkgsConfig = {
        config = { allowUnfree = true; };
        # overlays = attrValues self.overlays;
        overlays = attrValues self.overlays ++ singleton (
          # Sub in x86 version of packages that don't build on Apple Silicon yet
          final: prev: (optionalAttrs (prev.stdenv.system == "aarch64-darwin") {
            inherit (final.pkgs-x86)
              # idris2
              # nix-index
              # purescript;
              niv;
          })
        );
      };

      # Shared home-manager configs
      homeManagerStateVersion = "22.05";
      homeManagerCommonConfig = {
        imports = attrValues self.homeManagerModules ++ [
          ./home
          { home.stateVersion = homeManagerStateVersion; }
        ];
      };

      # Modules shared by most `nix-darwin` personal configurations.
      nixDarwinCommonModules = attrValues self.darwinModules ++ [
        # Main `nix-darwin` config
        ./darwin
        # `home-manager` module
        home-manager.darwinModules.home-manager
        (
          { config, lib, pkgs, ... }:
          let
            inherit (config.users) primaryUser;
          in
          {
            nixpkgs = nixpkgsConfig;
            # Hack to support legacy worklows that use `<nixpkgs>` etc.
            nix.nixPath = { nixpkgs = "$HOME/dotfiles.nix/nixpkgs.nix"; };
            # `home-manager` config
            users.users.${primaryUser}.home = "/Users/${primaryUser}";
            home-manager.useGlobalPkgs = true;
            home-manager.users.${primaryUser} = homeManagerCommonConfig;
            # Add a registry entry for this flake
            nix.registry.my.flake = self;
          }
        )
      ];
    in
    {
      # `nix-darwin` configs
      darwinConfigurations = rec {
        # Mininal configurations to bootstrap systems
        bootstrap-x86 = makeOverridable darwinSystem {
          system = "x86_64-darwin";
          modules = [ ./darwin/bootstrap.nix { nixpkgs = nixpkgsConfig; } ];
        };
        bootstrap-arm = bootstrap-x86.override { system = "aarch64-darwin"; };

        # M1 MBP
        matbook = darwinSystem {
          system = "aarch64-darwin";
          modules = nixDarwinCommonModules ++ [
            {
              users.primaryUser = "mat";
              networking.computerName = "matbook pro m1";
              networking.hostName = "matbook";
              networking.knownNetworkServices = [
                "Wi-Fi"
              ];
            }
          ];
        };

        # Config with small modifications needed/desired for CI with GitHub workflow
        githubCI = darwinSystem {
          system = "x86_64-darwin";
          modules = nixDarwinCommonModules ++ [
            ({ lib, ... }: {
              users.primaryUser = "runner";
              homebrew.enable = lib.mkForce false;
            })
          ];
        };

        # Build and activate with `nix build .#cloudVM.activationPackage; ./result/activate`
        cloudVM = home-manager.lib.homeManagerConfiguration {
          system = "x86_64-linux";
          stateVersion = homeManagerStateVersion;
          homeDirectory = "/home/mat";
          username = "mat";
          configuration = {
            imports = [ homeManagerCommonConfig ];
            nixpkgs = nixpkgsConfig;
          };
        };

        #     attrValues self.darwinModules ++ [ 
        #       # Main `nix-darwin` config
        #       ./configuration.nix
        #       # `home-manager` module
        #       home-manager.darwinModules.home-manager
        #       {
        #         nixpkgs = nixpkgsConfig;
        #         # `home-manager` config
        #         home-manager.useGlobalPkgs = true;
        #         home-manager.useUserPackages = true;
        #         home-manager.users.mat = import ./home.nix;            
        #       }
        #     ];
        #   };
      };

      # Overlays --------------------------------------------------------------- {{{

      overlays = {
        # nixpkgs overlays
        pkgs-stable = final: prev: {
          pkgs-stable = import inputs.nixpkgs {
            inherit (prev.stdenv) system;
            inherit (nixpkgsConfig) config;
          };
        };

        pkgs-unstable = final: prev: {
          pkgs-unstable = import inputs.nixpkgs-unstable {
            inherit (prev.stdenv) system;
            inherit (nixpkgsConfig) config;
          };
        };

        colors = import ./overlays/colors.nix;

        # Overlay useful on Macs with Apple Silicon
        apple-silicon = final: prev: optionalAttrs (prev.stdenv.system == "aarch64-darwin") {
          # Add access to x86 packages system is running Apple Silicon
          pkgs-x86 = import inputs.nixpkgs-unstable {
            system = "x86_64-darwin";
            inherit (nixpkgsConfig) config;
          };
        };
      };

      # `nix-darwin` modules (some are pending upstream acceptance)
      darwinModules = {
        programs-nix-index = import ./modules/darwin/programs/nix-index.nix;
        security-pam = import ./modules/darwin/security/pam.nix;
        users = import ./modules/darwin/users.nix;
      };

      # home manager configurations
      homeManagerModules = {
        # configs-git-aliases = import ./home/configs/git-aliases.nix;
        # configs-gh-aliases = import ./home/configs/gh-aliases.nix;
        configs-starship-symbols = import ./home/configs/starship-symbols.nix;
        programs-neovim-extras = import ./modules/home/programs/neovim/extras.nix;
        programs-kitty-extras = import ./modules/home/programs/kitty/extras.nix;
      };

    } // flake-utils.lib.eachDefaultSystem (system: {
      legacyPackages = import inputs.nixpkgs-unstable {
        inherit system;
        inherit (nixpkgsConfig) config;
        overlays = with self.overlays; [
          pkgs-unstable
          pkgs-stable
          colors
          apple-silicon
        ];
      };
    });
}