#!/usr/bin/env nix-shell
#! nix-shell -i bash -p jq
set -euo pipefail

## Configuration

libexec_dir="${0%/*}"
configuration=${NIXOS_CONFIG:-$libexec_dir/configuration.nix}
format=
format_dir=$libexec_dir/formats
target_system=
cores=
run=

## Functions

showUsage() {
  cat <<USAGE
Usage: $0 [options]

Options:

* --help: shows this help
* -c, --configuration PATH:
    select the nixos configuration to build. Default: $configuration
* -f, --format NAME: select one of the pre-determined formats
* --format-path PATH: pass a custom format
* --list: list the available built-in formats
* --run: runs the configuration in a VM
         only works for the "vm" and "vm-no-gui" formats
* --system: specify the target system (eg: x86_64-linux)
* --cores : to control the maximum amount of parallelism. (see nix-build documentation)
USAGE
}

listFormats() {
  for format in "$format_dir"/*.nix; do
    basename "$format" ".nix"
  done
}

abort() {
  echo "aborted: $*" >&2
  exit 1
}

## Main ##

while [[ $# -gt 0 ]]; do
  case "$1" in
    -c | --configuration)
      configuration=$2
      shift
      ;;
    --cores)
      cores=$2
      shift
      ;;
    -f | --format)
      format=$format_dir/$2.nix
      shift
      ;;
    --format-path)
      format=$2
      shift
      ;;
    --help)
      showUsage
      exit
      ;;
    --list)
      listFormats
      exit
      ;;
    --run)
      run=1
      # default to the VM format
      if [[ -z $format ]]; then
        format=$format_dir/vm.nix
      fi
      ;;
    --system)
      target_system=$2
      shift
      ;;
    *)
      abort "unknown option $1"
      ;;
  esac
  shift
done

if [[ -z $format ]]; then
  abort "missing format. use --help for more details"
fi

args=(
  "$libexec_dir/nixos-generate.nix"
  -I "nixos-config=$configuration"
  -I "format-config=$format"
)

if [[ -n $target_system ]]; then
  args+=(--argstr system "$target_system")
fi

if [[ -n $cores ]]; then
  args+=(--cores "$cores")
fi

formatAttr=$(nix-instantiate "${args[@]}" --eval --json -A config.formatAttr | jq -r .)

out=$(nix-build "${args[@]}" --no-out-link -A "config.system.build.$formatAttr")

if [[ -z $run ]]; then
  # show the first file
  find "$out" -type f -print -quit
else
  runner=$(find "$out"/bin -type l -print -quit)
  exec "$runner"
fi