{
  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;
    };
    nix-filter = {
      url = "github:numtide/nix-filter";
    };
  };

  outputs = {
    self,
    nixpkgs,
    nix-filter,
    ...
  }: 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/";
      pkgs = nixpkgsFor.${system};
      inherit (pkgs) lib overlays;
    in rec {
      p1 = nixpkgsFor.${system}.poetry2nix.mkPoetryApplication {
        name = "p1";
        projectDir = ./p1;
        meta = {
          description = self.description + ": p1";
          homepage = baseurl + "p1";
          license = nixpkgs.lib.licenses.gpl3;
          maintainers = ["wanderer"];
          platforms = lib.platforms.linux ++ lib.platforms.darwin;
        };
      };

      p2 = with pkgs;
        buildGo119Module rec {
          pname = "p2";
          buildInputs = [
            go_1_19
            gcc

            python3Packages.numpy
            python3Packages.pandas
            python3Packages.matplotlib
            python3Packages.scipy
            python3Packages.pybindgen
            libxcrypt
          ];
          nativeBuildInputs = [pkgconfig];

          overrideModAttrs = _: {
            # GOPROXY = "direct";
            GOFLAGS = "-buildmode=pie -trimpath -mod=readonly -modcacherw";
          };

          inherit version;
          doCheck = false;
          # use go.mod for managing go deps, instead of vendor-only dir
          proxyVendor = true;
          tags = []; # go "-tags" to build with
          ldflags = [
            "-s"
            "-w"
            "-X main.version=${version}"
          ];

          # dont't forget to update vendorSha256 whenever go.mod or go.sum change
          vendorSha256 = "sha256-Ns3ohAzZliK75fM6ryWubhfLBCVwU7CsZbuuzZrGaRY=";

          # In 'nix develop', we don't need a copy of the source tree
          # in the Nix store.
          src = nix-filter.lib.filter {
            # when in doubt, check out
            # https://github.com/numtide/nix-filter#design-notes
            # tl;dr: it'd be best to include folders, however there are
            # currently issues with that approach.
            root = lib.cleanSource ./p2;
            exclude = [
              ./p2/README.md

              ./p1

              ./flake.nix
              ./flake.lock
              ./default.nix
              ./shell.nix
              ./overlay.nix

              ./README.md

              ./.envrc
              ./.gitattributes
              ./.gitignore
              ./.golangci.yml
              ./.editorconfig
              ./.pre-commit-config.yaml

              # program output
              ./out
              ./res

              # nix result symlink
              ./result

              # the entire .git folder
              ./.git
            ];
          };

          meta = {
            description = "implementation of task 2 for ak9im";
            homepage = baseurl + "p2";
            license = lib.licenses.gpl3;
            maintainers = ["wanderer"];
            platforms = lib.platforms.linux ++ lib.platforms.darwin;
          };
        };

      p3 = with pkgs;
        buildGo119Module rec {
          pname = "p3";
          buildInputs = [
            go_1_19
            gcc

            python3Packages.numpy
            python3Packages.pandas
            python3Packages.matplotlib
            python3Packages.scipy
            python3Packages.pybindgen
            libxcrypt
          ];
          nativeBuildInputs = [pkgconfig];

          overrideModAttrs = _: {
            # GOPROXY = "direct";
            GOFLAGS = "-buildmode=pie -trimpath -mod=readonly -modcacherw";
          };

          inherit version;
          doCheck = false;
          # use go.mod for managing go deps, instead of vendor-only dir
          proxyVendor = true;
          tags = []; # go "-tags" to build with
          ldflags = [
            "-s"
            "-w"
            "-X main.version=${version}"
          ];

          # dont't forget to update vendorSha256 whenever go.mod or go.sum change
          vendorSha256 = "sha256-QXY1MN32g4WSyXfZDpR2C5TzP0lHgmecT7Jv4Dtf1Bk=";

          # In 'nix develop', we don't need a copy of the source tree
          # in the Nix store.
          src = nix-filter.lib.filter {
            # when in doubt, check out
            # https://github.com/numtide/nix-filter#design-notes
            # tl;dr: it'd be best to include folders, however there are
            # currently issues with that approach.
            root = lib.cleanSource ./p3;
            exclude = [
              ./p3/README.md

              ./p3

              ./flake.nix
              ./flake.lock
              ./default.nix
              ./shell.nix
              ./overlay.nix

              ./README.md

              ./.envrc
              ./.gitattributes
              ./.gitignore
              ./.golangci.yml
              ./.editorconfig
              ./.pre-commit-config.yaml

              # program output
              ./out
              ./res

              # nix result symlink
              ./result

              # the entire .git folder
              ./.git
            ];
          };

          meta = {
            description = "implementation of task 3 for ak9im";
            homepage = baseurl + "p3";
            license = lib.licenses.gpl3;
            maintainers = ["wanderer"];
            platforms = lib.platforms.linux ++ lib.platforms.darwin;
          };
        };

      default = p1;
    });

    apps = forAllSystems (system: rec {
      p1 = {
        type = "app";
        program = "${self.packages.${system}.${projname}}/bin/p1";
      };
      p2 = {
        type = "app";
        program = "${self.packages.${system}.${projname}}/bin/p2";
      };
      p3 = {
        type = "app";
        program = "${self.packages.${system}.${projname}}/bin/p3";
      };
      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;

        GOFLAGS = "-buildmode=pie -trimpath -mod=readonly -modcacherw";
        GOLDFLAGS = "-s -w -X main.version=${version}";
        CGO_CFLAGS = "-g0 -Ofast -mtune=native -flto";
        CGO_LDFLAGS = "-Wl,-O1,-sort-common,-as-needed,-z,relro,-z,now,-flto -pthread";

        shellHook = ''
          echo " -- in ${projname} dev shell..."
        '';

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

          # deps
          python3Packages.numpy
          python3Packages.pandas
          python3Packages.matplotlib
          python3Packages.scipy
          python3Packages.pybindgen
          poetry
          libxcrypt

          go_1_19
          go-tools
          gopls
          gofumpt
        ];
      };
    });
  };
}