{
  description = "Identification and modeling of stochastic signals - protocols";
  inputs = {
    nixpkgs.url = "github:NixOS/nixpkgs/nixpkgs-unstable";
    flake-compat = {
      url = "github:edolstra/flake-compat";
      flake = false;
    };
  };

  outputs = {
    self,
    nixpkgs,
    ...
  }: let
    projname = "ak9im";

    # to work with older version of flakes
    lastModifiedDate =
      self.lastModifiedDate or self.lastModified or "19700101";

    # Generate a user-friendly version number.
    version = "v0.0.0";

    supportedSystems = ["x86_64-linux" "x86_64-darwin" "aarch64-linux" "aarch64-darwin"];
    forAllSystems = nixpkgs.lib.genAttrs supportedSystems;
    pkgs = forAllSystems (system: nixpkgs.legacyPackages.${system});
    # Nixpkgs instantiated for supported system types.
    nixpkgsFor = forAllSystems (system:
      import nixpkgs {
        inherit system;
        overlays = [
          # no overlay imports atm
          # (import ./overlay.nix)
        ];
      });
  in {
    formatter = forAllSystems (
      system:
        nixpkgsFor.${system}.alejandra
    );
    packages = forAllSystems (system: let
      baseurl = "https://git.dotya.ml/wanderer/ak9im/";
    in rec {
      p1 = pkgs.${system}.poetry2nix.mkPoetryApplication {
        name = "p1";
        projectDir = ./p1;
        meta = {
          description = self.description + ": p1";
          homepage = baseurl + "p1";
          license = nixpkgs.lib.licenses.gpl3;
          maintainers = ["wanderer"];
          platforms = nixpkgs.lib.platforms.linux ++ nixpkgs.lib.platforms.darwin;
        };
      };
      default = p1;
    });

    apps = forAllSystems (system: rec {
      p1 = {
        type = "app";
        program = "${self.packages.${system}.${projname}}/bin/p1";
      };
      default = p1;
    });

    devShells = forAllSystems (system: let
      upcache = pkgs.writeShellScriptBin "upcache" ''
        ## refs:
        ##   https://fzakaria.com/2020/08/11/caching-your-nix-shell.html
        ##   https://nixos.wiki/wiki/Caching_nix_shell_build_inputs
        nix-store --query --references $(nix-instantiate shell.nix) | \
          xargs nix-store --realise | \
          xargs nix-store --query --requisites | \
          cachix push ${projname}
        nix build --json \
          | jq -r '.[].outputs | to_entries[].value' \
          | cachix push ${projname}
      '';
      add-license = pkgs.writeShellScriptBin "add-license" ''
        go run github.com/google/addlicense@v1.0.0 -v \
          -c "wanderer <a_mirre at utb dot cz>" \
          -l "GPL-3.0-or-later" -s .
      '';
    in {
      default = pkgs.${system}.mkShellNoCC {
        name = "${projname}-" + version;
        shellHook = ''
          echo " -- in ${projname} dev shell..."
        '';

        packages = with pkgs.${system}; [
          (poetry2nix.mkPoetryEnv {projectDir = ./p1;})
          # ux
          python3Packages.pynvim
          python3Packages.jedi
          pre-commit

          # deps
          python3Packages.numpy
          python3Packages.pandas
          python3Packages.matplotlib
          python3Packages.scipy
          poetry
        ];
      };
    });
  };
}