#!/bin/sh
#
# Copyright (c) 2025, Barcelona Supercomputing Center (BSC)
# SPDX-License-Identifier: GPL-3.0+
# Author: Rodrigo Arias Mallo <rodrigo.arias@bsc.es>

function usage() {
  echo "USAGE: nixgen [-f] [package [...]] [-b package [...]]" >&2
  echo "  Generates a flake.nix file with the given packages." >&2
  echo "  After flake.nix is created, use 'nix develop' to enter the shell." >&2
  echo "OPTIONS" >&2
  echo "  -f               Overwrite existing flake.nix (default: no)." >&2
  echo "  packages...      Add these packages to the shell." >&2
  echo "  -b packages...   Add the dependencies needed to build these packages." >&2
  echo "EXAMPLE" >&2
  echo "  $ nixgen ovni bigotes -b nosv tampi" >&2
  echo "  Adds the packages ovni and bigotes as well as all required dependencies" >&2
  echo "  to build nosv and tampi." >&2
  echo "AUTHOR" >&2
  echo "  Rodrigo Arias Mallo <rodrigo.arias@bsc.es>" >&2
  exit 1
}

mode=package
packages=
inputsFrom=
force=

if [[ $# -eq 0 ]]; then
  usage
fi

while [[ $# -gt 0 ]]; do
    case $1 in -b)
      mode=build
      shift
      ;;
    -f)
      force=1
      shift
      ;;
    -h)
      usage
      ;;
    -*|--*)
      echo "error: unknown option $1" >&2
      exit 1
      ;;
    *)
      if [ "$mode" == "package" ]; then
        packages+="${packages:+ }$1"
      else
        inputsFrom+="${inputsFrom:+ }$1"
      fi
      shift
      ;;
  esac
done

if [ ! "$force" -a -e flake.nix ]; then
  echo "error: flake.nix exists, force overwrite with -f" >&2
  exit 1
fi

cat > flake.nix <<EOF
{
  inputs.jungle.url = "git+https://jungle.bsc.es/git/rarias/jungle";
  outputs = { self, jungle }:
  let
    nixpkgs = jungle.inputs.nixpkgs;
    customOverlay = (final: prev: {
      # Example overlay, for now empty
    });
    pkgs = import nixpkgs {
      system = "x86_64-linux";
      overlays = [
        # Apply jungle overlay to get our BSC custom packages
        jungle.outputs.bscOverlay
        # And on top apply our local changes to customize for cluster
        customOverlay
      ];
    };
  in {
    devShells.x86_64-linux.default = pkgs.mkShell {
      pname = "devshell";
      # Include these packages in the shell
      packages = with pkgs; [
        $packages
      ];
      # The dependencies needed to build these packages will be also included
      inputsFrom = with pkgs; [
        $inputsFrom
      ];
    };
  };
}
EOF