flake.nix

{
  description = "An sbt plugin to monitor energy usage during command runs";

  # Nixpkgs / NixOS version to use.
  inputs.nixpkgs.url = "nixpkgs/nixos-21.11";

  outputs = { self, nixpkgs }:
    let

      # Generate a user-friendly version number.
      version = builtins.substring 0 8 self.lastModifiedDate;

      # System types to support.
      supportedSystems = [ "x86_64-linux" "x86_64-darwin" "aarch64-linux" "aarch64-darwin" ];

      # Helper function to generate an attrset '{ x86_64-linux = f "x86_64-linux"; ... }'.
      forAllSystems = nixpkgs.lib.genAttrs supportedSystems;

      # Nixpkgs instantiated for supported system types.
      nixpkgsFor = forAllSystems (system: import nixpkgs { inherit system; });

    in
    {

      # Provide some binary packages for selected system types.
      packages = forAllSystems (system:
        let
          pkgs = nixpkgsFor.${system};
          sbt = pkgs.sbt.override { jre = pkgs.openjdk8; };
        in
        {
          energymonitor-plugin = pkgs.stdenv.mkDerivation {
            name = "sbt-energymonitor";
            buildInputs = [ sbt ];
            src = ./.;
          };
        });

      # The default package for 'nix build'. This makes sense if the
      # flake provides only one package or there is a clear "main"
      # package.
      defaultPackage = forAllSystems (system: self.packages.${system}.energymonitor-plugin);
      devShell = forAllSystems (system:
        let pkgs = nixpkgsFor.${system};
        in
        pkgs.mkShell {
          buildInputs = with pkgs; [ sbt pkgs.openjdk8 pkgs.nodejs-14_x ];
        });

    };
}