{
  description = "User management system.";

  inputs = {
    flake-utils.url = "github:numtide/flake-utils";
  };

  outputs = inputs @ { self, nixpkgs, ... }:
    inputs.flake-utils.lib.eachDefaultSystem (system:
      let pkgs = nixpkgs.legacyPackages.${system};
          myGo = "${pkgs.go}/bin/go";
          myBuf = "${pkgs.buf}/bin/buf";
          myDir = "$MY_USERS_DIR";
          myBuild = pkgs.writeShellScriptBin "users-build" ''
            pushd ${myDir} > /dev/null &&
            sed -n 's,https://petstore.swagger.io/v2/swagger.json,swagger.json,g' \
              ${myDir}/modules/swagger-ui/dist/swagger-initializer.js &&
            ${myBuf} build &&
            ${myBuf} generate &&
            ${myGo} build -o ${myDir}/bin/users-server ${myDir}/cmd/server/main.go &&
            popd > /dev/null
          '';
      in
        rec {
          devShells.default = pkgs.mkShell {
            buildInputs = with pkgs; [
              go
              gopls
              protoc-gen-go
              protoc-gen-go-grpc

              buf
              grpc
              grpcui
              grpcurl
              grpc-tools
              grpc-gateway

              myBuild
            ];

            shellHook = ''
              export MY_USERS_DIR="$(pwd)"
              export GO111MODULE=on
              export GOPATH=$XDG_DATA_HOME/go
              export PATH=$GOPATH/bin:$PATH
              export PATH=$MY_USERS_DIR/bin:$PATH
            '';
          };
        }
    );
}