{
  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";

    # Flake helpers
    flake-utils.url = "github:numtide/flake-utils";
    flake-compat.url = "github:edolstra/flake-compat";
    flake-compat.flake = false;

    # Extra sources
    helix.url = "github:helix-editor/helix";
    helix.inputs.nixpkgs.follows = "nixpkgs-unstable";
    dark-mode-notify-src.url = "github:bouk/dark-mode-notify";
    dark-mode-notify-src.flake = false;
    kitty-icon.url = "github:DinkDonk/kitty-icon";
    kitty-icon.flake = false;
  };

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

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

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

      homeManagerStateVersion = "22.05";

      primaryUserInfo = {
        username = "mat";
        fullName = "mat ess";
        email = "mat@mat.services";
        nixConfigDirectory = "/Users/mat/dotfiles.nix";
      };

      workUserInfo = {
        username = "mess";
        fullName = "Matthew Ess";
        email = "mess@yelp.com";
        nixConfigDirectory = "/Users/mess/dotfiles.nix";
      };

      # Modules shared by most `nix-darwin` personal configurations.
      nixDarwinCommonModules = attrValues self.darwinModules ++ [
        # `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>`, darwin-option, etc.
            nix.nixPath = {
              nixpkgs = "${inputs.nixpkgs-unstable}";
              darwin = "${inputs.darwin}";
            };
            # `home-manager` config
            users.users.${primaryUser.username}.home = "/Users/${primaryUser.username}";
            home-manager.useGlobalPkgs = true;
            home-manager.users.${primaryUser.username} = {
              imports = attrValues self.homeManagerModules;
              home.stateVersion = homeManagerStateVersion;
              home.primaryUser = primaryUser;
              home.enableNixpkgsReleaseCheck = true;
            };
            # 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 = primaryUserInfo;
              networking.computerName = "matbook pro m1";
              networking.hostName = "matbook";
              networking.knownNetworkServices = [
                "Wi-Fi"
              ];
              nix.settings.cores = 2;
              nix.settings.max-jobs = 4;

              environment.systemPackages = with pkgs; [
                vscodium
              ];
              games.enable = true;
              home-manager.sharedModules = [{
                programs.fish.shellAliases = {
                  code = "${pkgs.vscodium}/bin/codium";
                };
                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 = workUserInfo;
              networking.knownNetworkServices = [
                "Wi-Fi"
              ];
              nix.settings.cores = 2;
              nix.settings.max-jobs = 5;

              games.enable = false;
              environment.systemPackages = with pkgs; [
                yubiswitch
                vscode
              ];
              homebrew.casks = [ "itsycal" ];
              home-manager.sharedModules = [{
                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 = primaryUserInfo // {
                username = "runner";
                nixConfigDirectory = "/Users/runner/work/nixpkgs/nixpkgs";
              };
              homebrew.enable = lib.mkForce false;
            })
          ];
        };

      };

      # Build and activate on new system with:
      # `nix build .#homeConfigurations.<name>.activationPackage; ./result/activate`
      homeConfigurations = rec {
        cloudVM = home-manager.lib.homeManagerConfiguration {
          pkgs = import inputs.nixpkgs-unstable {
            system = "x86_64-linux";
            inherit (nixpkgsConfig) config overlays;
          };
          modules = attrValues self.homeManagerModules ++ [
            ({ config, ... }: {
              home.username = config.home.primaryUser.username;
              home.homeDirectory = "/home/${config.home.username}";
              home.stateVersion = homeManagerStateVersion;
              home.primaryUser = primaryUserInfo // {
                nixConfigDirectory = "${config.home.homeDirectory}/dotfiles.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;
          };
        };

        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; };
        };
      };

      # `nix-darwin` configs and modules
      darwinModules = {
        # configs
        bootstrap = import ./darwin/bootstrap.nix;
        defaults = import ./darwin/defaults.nix;
        general = import ./darwin/general.nix;
        homebrew = import ./darwin/homebrew.nix;
        # modules
        games = import ./modules/darwin/games.nix;
        primary-user = import ./modules/darwin/primary-user.nix;
      };

      # home manager configurations
      homeManagerModules = {
        # configs
        configs-starship-symbols = import ./home/configs/starship-symbols.nix;
        copyApplications = import ./home/copyApplications.nix;
        # services
        dark-mode-notify-service = import ./home/services/dark-mode-notify.nix;
        tarsnap-service = import ./home/services/tarsnap.nix;
        # etc
        files = import ./home/files.nix;
        fish = import ./home/fish.nix;
        git = import ./home/git.nix;
        kitty = import ./home/kitty.nix;
        programs = import ./home/programs.nix;
        starship = import ./home/starship.nix;
        # modules
        # TODO: migrate to helix
        # programs-kakoune-extras = import ./modules/home/programs/kakoune/extras.nix;
        programs-kitty-extras = import ./modules/home/programs/kitty/extras.nix;
        home-primary-user = { lib, ... }: {
          options.home.primaryUser =
            (self.darwinModules.primary-user { inherit lib; }).options.users.primaryUser;
        };
      };

    } // 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
        ];
      };
    });
}