{
  description = "pbsds' system/home flake";

  inputs = {
    nixpkgs.url      = "github:NixOS/nixpkgs/nixos-23.05";
    unstable.url     = "github:NixOS/nixpkgs/nixos-unstable";
    home-manager.url = "github:nix-community/home-manager/release-23.05";
    home-manager.inputs.nixpkgs.follows = "nixpkgs";
    nixos-hardware.url = "github:NixOS/nixos-hardware";

    #TODO:
    #sops-nix.url = "github:Mic92/sops-nix";
    #sops-nix.inputs.nixpkgs.follows = "nixpkgs";
    #matrix-next.url = "github:dali99/nixos-matrix-modules"; # see https://git.pvv.ntnu.no/Drift/pvv-nixos-config/src/main/flake.nix
    #https://github.com/considerate/nixos-odroidhc4
    #https://cyberchaos.dev/cyberchaoscreatures/musl-nixos/
    #https://github.com/numtide/system-manager
    #nix-vscode-extensions.url = "github:nix-community/nix-vscode-extensions"
    #https://github.com/numtide/nixpkgs-unfree # has a cache
    #https://github.com/matthewbauer/nixiosk
    #inputs.pre-commit-hooks.url = "github:cachix/pre-commit-hooks.nix";

    # used to host old docs
    #nixpkgs-22.url = "github:NixOS/nixpkgs/nixos-22.11";
    #nixpkgs-21.url = "github:NixOS/nixpkgs/nixos-21.11";
    #nixpkgs-20.url = "github:NixOS/nixpkgs/nixos-20.09";
    #nixpkgs-19.url = "github:NixOS/nixpkgs/nixos-19.09";
    #nixpkgs-19.flake = false; # Earlier versions are not flake-pure

    # TODO: somehow make these private repos optional (a lazy fetch would be nice)
    pbsds-papers.url = "git+ssh://git@github.com/pbsds/papers.git";
  };

  nixConfig.extra-substituters = [
    "https://cuda-maintainers.cachix.org"
    "https://nix-community.cachix.org"
    "https://nixos-rocm.cachix.org"
    "https://nixpkgs-unfree.cachix.org"
    "https://numtide.cachix.org"
  ];
  nixConfig.extra-trusted-public-keys = [
    "cuda-maintainers.cachix.org-1:0dq3bujKpuEPMCX6U4WylrUDZ9JyUG0VpVZa7CNfq5E="
    "nix-community.cachix.org-1:mB9FSh9qf2dCimDSUo8Zy7bkq5CX+/rkCWyvRCYg3Fs="
    "nixos-rocm.cachix.org-1:VEpsf7pRIijjd8csKjFNBGzkBqOmw8H9PRmgAq14LnE="
    "nixpkgs-unfree.cachix.org-1:hqvoInulhbV4nJ9yJOEr+4wxhDV4xq2d1DK7S6Nj6rs="
    "numtide.cachix.org-1:2ps1kLBUWjxIneOy1Ik6cQjb41X0iXVXeHigGmycPPE="
  ];

  outputs = {
    self,
    nixpkgs,
    unstable,
    nixos-hardware,
    home-manager,
    ...
  } @ inputs:
  let
    flake = inputs: system: nixpkgs.lib.mapAttrs (name: flake: {
      # TODO filter non-flake inputs
      nixos = flake.nixosModules
        or null;
      pkgs = flake.packages.${system}
        or flake.legacyPackages.${system}
        or null;
      lib = flake.lib.${system}
        or flake.lib
        or null;
    }) inputs;
    forSystems = systems: f: nixpkgs.lib.genAttrs systems (system: f rec {
      inherit system;
      pkgs = nixpkgs.legacyPackages.${system};
      lib  = nixpkgs.legacyPackages.${system}.lib;
      flakes = flake inputs system;
    });
    forAllSystems = forSystems [
      "x86_64-linux"
      "aarch64-linux"
      #"riscv64-linux"
    ];

    mkConfig = hostname: domain: system: modules: nixpkgs.lib.nixosSystem {
      inherit system;
      specialArgs = {
        inherit inputs;
        flakes = flake inputs system;
      };
      modules = modules ++ [ ./base.nix "${self}/hosts/${hostname}" ({
        home-manager.extraSpecialArgs = {
          inherit inputs;
          flakes = flake inputs system;
        };
        # still needed even if using networkd
        networking.hostName = hostname;
        networking.domain   = domain;
        networking.search = [ domain ];
        nixpkgs.overlays = [
          (final: prev: {
            #unstable = unstable.legacyPackages.${final.system};
            unstable = import unstable { inherit system; config.allowUnfree = true; }; # TODO: inherit nixos config from stable
          })
        ];
        # This makes commandline tools like 'nix run nixpkgs#hello'
        # and 'nix-shell -p hello' use the same channel as system was built with
        nix.registry.nixpkgs.flake  = inputs.nixpkgs;
        nix.registry.nixpkgs-unstable.flake = inputs.unstable;
        #nix.registry.nixpkgs-unstable.flake.url = "github:NixOS/nixpkgs/nixos-unstable";
        nix.nixPath = [
          "nixpkgs=${inputs.nixpkgs}"
          "nixpkgs-unstable=${inputs.unstable}"
          #"nixpkgs-unstable=github:NixOS/nixpkgs/nixos-unstable"
        ];
      })];
    };
  in {
    inherit inputs;

    packages = forAllSystems ({ pkgs, flakes, ... }: {
      mpv-webm = pkgs.callPackage ./pkgs/mpv-webm.nix {}; # TODO: https://github.com/NixOS/nixpkgs/pull/238659
      nixos-rebuild-nom = with pkgs; writeScriptBin "nixos-rebuild" ''
        exec ${nixos-rebuild}/bin/nixos-rebuild "$@" |& ${nix-output-monitor}/bin/nom
      '';
    });

    lib = {
      inherit flake forSystems;
    } // forAllSystems ({ ... }: {
      inherit flake forSystems;
    });

    nixosConfigurations = let nm = nixos-hardware.nixosModules; in {
      # TODO: move nixos-hardware imports to the nixos configs?
      noximilien = mkConfig "noximilien" "pbsds.net" "x86_64-linux" (with nm; [ common-pc common-pc-ssd common-cpu-intel ]);
      bolle      = mkConfig "bolle"      "pbsds.net" "x86_64-linux" (with nm; [ common-pc common-pc-ssd common-cpu-intel ]);
      nord       = mkConfig "nord"       "pbsds.net" "x86_64-linux" (with nm; [ common-pc common-pc-ssd common-cpu-intel-cpu-only common-cpu-intel-sandy-bridge common-gpu-amd common-hidpi ]);
      sopp       = mkConfig "sopp"       "pbsds.net" "x86_64-linux" (with nm; [ common-pc common-pc-ssd common-cpu-intel common-gpu-nvidia ]);
    };

    homeConfigurations = forAllSystems ({ pkgs, flakes, ... }: let
      mkHome = user: home: modules: home-manager.lib.homeManagerConfiguration {
        inherit pkgs;
        modules = modules ++ [{
          home.username = user;
          home.homeDirectory = home;
        }];
        extraSpecialArgs.flakes = flakes;
      };
    in {
      pbsds       = mkHome "pbsds" "/home/pbsds" [ ./users/pbsds/home ];
      pbsds-gnome = mkHome "pbsds" "/home/pbsds" [ ./users/pbsds/home/gnome.nix ];
    });

    devShells = forAllSystems ({ pkgs, flakes, ... }: let
      mkShell = packages: pkgs.mkShellNoCC { inherit packages; };
      envrc-pkgs = [
        flakes.self.pkgs.nixos-rebuild-nom
        pkgs.home-manager
        pkgs.nix-output-monitor
        pkgs.cachix
      ];
    in {
      envrc-local  = mkShell envrc-pkgs;
      envrc-remote = mkShell (envrc-pkgs ++ [
        flakes.unstable.pkgs.remote-exec # TODO: stable
        pkgs.yq
        pkgs.rsync
      ]);
      remoteenv = mkShell [
        flakes.self.pkgs.nixos-rebuild-nom
      ];
    });

  };
}