{
  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;
    nixpkgs-master.url = github:NixOS/nixpkgs/master;

    # 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";

    # Config "flag" for disabling homebrew
    homebrew-enabled.url = github:boolean-option/true;

    # Other sources
    flake-utils.url = github:numtide/flake-utils;
    flake-compat = {
      url = github:edolstra/flake-compat;
      flake = false;
    };
    dark-mode-notify-src = {
      url = github:bouk/dark-mode-notify;
      flake = false;
    };
    luar-src = {
      url = github:gustavo-hms/luar;
      flake = false;
    };
    smarttab-kak-src = {
      url = github:andreyorst/smarttab.kak;
      flake = false;
    };
    auto-pairs-kak-src = {
      url = github:alexherbo2/auto-pairs.kak;
      flake = false;
    };
    kakoune-sudo-write-src = {
      url = github:occivink/kakoune-sudo-write;
      flake = false;
    };
    kitty-icon = {
      url = github:DinkDonk/kitty-icon;
      flake = false;
    };
  };

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

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

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

      # 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 ++ [
            ({ pkgs, ... }: {
              users.primaryUser = "mat";
              networking.computerName = "matbook pro m1";
              networking.hostName = "matbook";
              networking.knownNetworkServices = [
                "Wi-Fi"
              ];
              nix.buildCores = 2;
              nix.maxJobs = 4;

              environment.systemPackages = with pkgs; [
                vscodium
              ];
              games.enable = true;
              home-manager.sharedModules = [{
                programs.git.userEmail = "mat@mat.services";
                programs.git.userName = "mat ess";
                programs.ssh.matchBlocks.remarkable = {
                  hostname = "10.11.99.1";
                  user = "root";
                  port = 22;
                };
                programs.vscode.package = pkgs.vscodium;
              }];
            })
          ];
        };

        yelpbook-m1 = darwinSystem {
          system = "aarch64-darwin";
          modules = nixDarwinCommonModules ++ [
            ({ pkgs, ... }: {
              users.primaryUser = "mess";
              networking.knownNetworkServices = [
                "Wi-Fi"
              ];
              nix.buildCores = 2;
              nix.maxJobs = 5;

              games.enable = false;
              environment.systemPackages = with pkgs; [
                yubiswitch
                vscode
              ];
              homebrew.casks = [ "itsycal" ];
              home-manager.sharedModules = [{
                programs.git.userEmail = "mess@yelp.com";
                programs.git.userName = "Matthew Ess";
                programs.ssh.matchBlocks.devbox = {
                  hostname = "amp1";
                  forwardAgent = true;
                  serverAliveInterval = 120;
                };
                programs.fish.functions.devbox.body = ''
                  ssh -t devbox "agenttmux attach; or agenttmux new -s yelp"
                '';
              }];
            })
          ];
        };

        # 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;
          };
        };
      };

      # 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;
          };
        };

        pkgs-master = final: prev: {
          pkgs-master = import inputs.nixpkgs-master {
            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;
          };
        };

        patched = final: prev: optionalAttrs prev.stdenv.isDarwin {
          inherit (inputs) kitty-icon;
          lib = prev.lib // { homebrew-enabled = inputs.homebrew-enabled.value; };
          kakounePlugins = prev.kakounePlugins // {
            auto-pairs-kak = prev.kakounePlugins.auto-pairs-kak.overrideAttrs (attrs: {
              src = inputs.auto-pairs-kak-src;
            });
          };
        };
      };

      # `nix-darwin` modules (some are pending upstream acceptance)
      darwinModules = {
        games = import ./modules/darwin/games.nix;
        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-kakoune-extras = import ./modules/home/programs/kakoune/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-master
          pkgs-stable
          colors
          apple-silicon
          patched
        ];
      };
    });
}