os/flake.nix

{
  description = "A highly structured configuration database.";

  inputs =
    {
      # Once desired, bump master's locked revision:
      # nix flake update --update-input master
      master.url = "nixpkgs/master";
      nixos.url = "nixpkgs/release-20.09";
      home.url = "github:nix-community/home-manager/release-20.09";
      flake-utils.url = "github:numtide/flake-utils/flatten-tree-system";
      devshell.url = "github:numtide/devshell";
      nixos-hardware.url = "github:nixos/nixos-hardware";
    };

  outputs = inputs@{ self, home, nixos, master, flake-utils, nur, devshell, nixos-hardware }:
    let
      inherit (builtins) attrValues;
      inherit (flake-utils.lib) eachDefaultSystem flattenTreeSystem;
      inherit (nixos.lib) recursiveUpdate;
      inherit (self.lib) overlays nixosModules genPackages pkgImport;

      externOverlays = [ nur.overlay devshell.overlay ];
      externModules = [ home.nixosModules.home-manager ];

      outputs =
        let
          system = "x86_64-linux";
          pkgs = self.legacyPackages.${system};
        in
        {
          inherit nixosModules overlays;

          nixosConfigurations =
            import ./hosts
              (recursiveUpdate inputs {
                inherit pkgs externModules system;
                inherit (pkgs) lib;
              });

          overlay = import ./pkgs;

          lib = import ./lib {
            inherit (nixos) lib;
          };

          templates.flk.path = ./.;

          templates.flk.description = "flk template";

          defaultTemplate = self.templates.flk;
        };
    in
    recursiveUpdate
      (eachDefaultSystem
        (system:
          let
            unstable = pkgImport master [ ] system;

            pkgs =
              let
                override = import ./pkgs/override.nix;
                overlays = [
                  (override unstable)
                  self.overlay
                  (final: prev: {
                    lib = (prev.lib or { }) // {
                      inherit (nixos.lib) nixosSystem;
                      flk = self.lib;
                      utils = flake-utils.lib;
                    };
                  })
                ]
                ++ (attrValues self.overlays)
                ++ externOverlays;
              in
              pkgImport nixos overlays system;

            packages = flattenTreeSystem system
              (genPackages {
                inherit self pkgs;
              });
          in
          {
            inherit packages;

            devShell = import ./shell {
              inherit pkgs nixos;
            };

            legacyPackages = pkgs;
          }
        )
      )
      outputs;
}