{
  inputs = {
    # nixpkgs.url = "github:nixOS/nixpkgs";
    nixpkgs.follows = "ocaml-overlay/nixpkgs";
    ocaml-overlay = {
      url = "github:nix-ocaml/nix-overlays";
    };
    flake-utils.url = "github:numtide/flake-utils";
  };

  outputs = {
    self,
    nixpkgs,
    flake-utils,
    ocaml-overlay,
  }: let
    version = builtins.toString self.lastModified;
  in
    flake-utils.lib.eachDefaultSystem (
      system: let
        pkgs = import nixpkgs {
          inherit system;
          overlays = [
            ocaml-overlay.overlays.default
          ];
          extra-substituters = "https://anmonteiro.nix-cache.workers.dev";
          extra-trusted-public-keys = "ocaml.nix-cache.com-1:/xI2h2+56rwFfKyyFVbkJSeGqSIYMC/Je+7XXqGKDIY=";
        };
        inherit (pkgs) mkShell ocaml-ng;
        inherit
          (ocaml-ng.ocamlPackages_5_2)
          dune_3
          ocaml
          utop
          ocaml-lsp
          ocamlformat
          ocamlformat-rpc-lib
          angstrom
          angstrom-unix
          ppx_inline_test
          ;
        minimal = [
          dune_3
          ocaml
          angstrom
          angstrom-unix
          ppx_inline_test
        ];
        dev = [
          utop
          ocaml-lsp
          ocamlformat
          ocamlformat-rpc-lib
          pkgs.just
        ];
      in {
        devShells.default = mkShell {
          buildInputs = minimal ++ dev;
          shellHook = let
            justFile = ''
              default:
                @just --list

              @build:
                nix build .#debug --offline

              @release:
                nix build --offline

              @test:
                printf "\\n\\n\\t************ running nix+dune tests ************\\n\\n\\n"
                nix flake check --offline
                nix build .#tests --offline
                printf "\\n\\n\\t************ running visual test ************\\n\\n\\n"
                echo one two three four | CULRS="(255,0,0);(0,0,255);#00FF00" CULR_ORDER="1;0;2" result/bin/culr
            '';
          in ''
            printf '${justFile}' > justfile
          '';
        };

        checks.default = pkgs.callPackage ./nix/test.nix {
          culr = self.packages.${system}.tests;
          inherit version;
        };

        packages.default = pkgs.callPackage ./nix/default.nix {
          ocaml-deps = minimal;
          inherit version;
        };

        packages.debug = pkgs.callPackage ./nix/default.nix {
          debug = true;
          ocaml-deps = minimal;
          inherit version;
        };

        packages.tests = pkgs.callPackage ./nix/default.nix {
          debug = true;
          ocaml-deps = minimal;
          doCheck = true;
          inherit version;
        };
      }
    )
    // {
      nixosModules.culr = import ./nix/module.nix {culrOverlay = self.overlays.culr;};

      overlays.culr = final: _prev: let
        ocaml-deps = let
          inherit
            (prev.ocaml-ng)
            dune_3
            ocaml
            angstrom
            angstrom-unix
            ppx_inline_test
            ;
        in [
          dune_3
          ocaml
          angstrom
          angstrom-unix
          ppx_inline_test
        ];
      in {
        culr = final.callPackage ./nix/default.nix {
          inherit ocaml-deps version;
        };
      };
    };
}