{ inputs, ... }:
{
  flake.nixosModules.nixUtils-laptop = { ... }: {
    # nixpkgs-review crashed my laptop multiple times. We must reduce how much ressources it can take.
    # for reference, my laptop is a 12 core ryzen 7
    nix.settings.max-jobs = 6;
    nix.settings.cores = 6;
  };
  flake.nixosModules.nixUtils = { pkgs-unstable, ... }: {
    # Garbage collector of generations
    nix.gc = {
      automatic = true;
      dates = "weekly";
      options = "--delete-older-than 7d"; # every week delete generations older than a month
    };
  
    #manix is unhappy without this
    nix.nixPath = [
      "nixpkgs=${inputs.nixpkgs.outPath}"
      "home-manager=${inputs.home-manager.outPath}"
    ];
  
    #adds nixos experimental features:
    nix.settings.experimental-features = ["nix-command" "flakes"];
  
    environment.systemPackages = with pkgs-unstable; [
      nixpkgs-review
      nixfmt-tree
      treefmt
      nixd
      deadnix
      alejandra
      vimPluginsUpdater # used for building plugins
      nix-index
      statix
    ];
  };
  flake.packages.custom-trimmer = { pkgs, ... }:
  # https://gist.github.com/MaxwellDupre/3077cd229490cf93ecab08ef2a79c852
  # better garbage collector
    pkgs.writeShellApplication {
    name = "custom-trimmer";
    runtimeInputs = with pkgs; [
      nix
    ];
    text = ''
      set -euo pipefail
  
      ## Defaults
      keepGensDef=30; keepDaysDef=7
      keepGens=$keepGensDef; keepDays=$keepDaysDef
  
      ## Usage
      usage () {
          printf "Usage:\n\t ./trim-generations.sh <keep-generations> <keep-days> <profile> \n\n
      (defaults are: Keep-Gens=%d Keep-Days=%d Profile=user)\n\n" "$keepGensDef" "$keepDaysDef"
          printf "If you enter any parameters, you must enter all three, or none to use defaults.\n"
          printf "Example:\n\t trim-generations.sh 15 10 home-manager\n"
          printf "  this will work on the home-manager profile and keep all generations from the\n"
          printf "last 10 days, and keep at least 15 generations no matter how old.\n"
          printf "\nProfiles available are:\tuser, home-manager, channels, system (root)\n"
          printf "\n-h or --help prints this help text."
      }
  
      if [ $# -eq 1 ]; then      # if help requested
          if [ "$1" = "-h" ]; then
               usage
               exit 1;
          fi
          if [ "$1" = "--help" ]; then
               usage
               exit 2;
          fi
          printf "Dont recognise your option exiting..\n\n"
          usage
          exit 3;
  
          elif [ $# -eq 0 ]; then            # print the defaults
              printf "The current defaults are:\n Keep-Gens=%d Keep-Days=%d \n\n" "$keepGensDef" "$keepDaysDef"
              read -r -p "Keep these defaults? (y/n):" answer
  
              case "$answer" in
              [yY1] )
                      printf "Using defaults..\n"
                  ;;
              [nN0] ) printf "ok, doing nothing, exiting..\n"
                  exit 6;
                  ;;
              *     ) printf "%b" "Doing nothing, exiting.."
                  exit 7;
                  ;;
              esac
      fi
  
      ## Handle parameters (and change if root)
      if [[ $EUID -ne 0 ]]; then              # if not root
          profile=$(readlink /home/"$USER"/.nix-profile)
      else
          if [ -d /nix/var/nix/profiles/system ]; then   # maybe this or the other
              profile="/nix/var/nix/profiles/system"
          elif [ -d /nix/var/nix/profiles/default ]; then
              profile="/nix/var/nix/profiles/default"
          else
              echo "Cant find profile for root. Exiting"
              exit 8
          fi
      fi
      if (( $# < 1 )); then
          printf "Keeping default: %d generations OR %d days, whichever is more\n" "$keepGensDef" "$keepDaysDef"
      elif [[ $# -le 2 ]]; then
          printf "\nError: Not enough arguments.\n\n" >&2
          usage
          exit 1
      elif (( $# > 4)); then
          printf "\nError: Too many arguments.\n\n" >&2
          usage
          exit 2
      else
          if [ "$1" -lt 1 ]; then
              printf "using Gen numbers less than 1 not recommended. Setting to min=1\n"
              read -r -p "is that ok? (y/n): " answer
              printf "%s" "$answer"
              case "$answer" in
              [yY1] )
                  printf "ok, continuing..\n"
                  ;;
              [nN0] )
                  printf "ok, doing nothing, exiting..\n"
                  exit 6;
                  ;;
              *     )
                  printf "%b" "Doing nothing, exiting.."
                  exit 7;
                  ;;
              esac
          fi
          if [ "$2" -lt 0 ]; then
              printf "using negative days number not recommended. Setting to min=0\n"
              read -r -p "is that ok? (y/n): " answer
  
              case "$answer" in
              [yY1] )
                  printf "ok, continuing..\n"
                  ;;
              [nN0] )
                  printf "ok, doing nothing, exiting..\n"
                  exit 6;
                  ;;
              *     )
                  printf "%b" "Doing nothing, exiting.."
                  exit 7;
                  ;;
              esac
          fi
          keepGens=$1; keepDays=$2;
          (( keepGens < 1 )) && keepGens=1
          (( keepDays < 0 )) && keepDays=0
          if [[ $EUID -ne 0 ]]; then
              if [[ $3 == "user" ]] || [[ $3 == "default" ]]; then
                  profile=$(readlink /home/"$USER"/.nix-profile)
              elif [[ $3 == "home-manager" ]]; then
                  # home-manager defaults to $XDG_STATE_HOME; otherwise, use
                  # `home-manager generations` and `nix-store --query --roots
                  # /nix/store/...` to figure out what reference is keeping the old
                  # generations alive.
                  profile="''${XDG_STATE_HOME:-$HOME/.local/state}/nix/profiles/home-manager"
              elif [[ $3 == "channels" ]]; then
                  profile="/nix/var/nix/profiles/per-user/$USER/channels"
              else
                  printf "\nError: Do not understand your third argument. Should be one of: (user / home-manager/ channels)\n\n"
                  usage
                  exit 3
              fi
          else
              if [[ $3 == "system" ]]; then
                  profile="/nix/var/nix/profiles/system"
              elif [[ $3 == "user" ]] || [[ $3 == "default" ]]; then
                  profile="/nix/var/nix/profiles/default"
              else
                  printf "\nError: Do not understand your third argument. Should be one of: (user / system)\n\n"
                  usage
                  exit 3
              fi
          fi
          printf "OK! \t Keep Gens = %s \t Keep Days = %s \n\n" "$keepGens" "$keepDays"
  
  
      fi
  
      printf "Operating on profile: %s \t \n\n" "$profile"
  
      ## Runs at the end, to decide whether to delete profiles that match chosen parameters.
      choose () {
          local default="$1"
          local prompt="$2"
          local answer
  
          read -r -p "$prompt" answer
          [ -z "$answer" ] && answer="$default"
  
          case "$answer" in
              [yY1] ) #printf "answered yes!\n"
                   nix-env --delete-generations -p "$profile" "''${!gens[@]}"
                  exit 0
                  ;;
              [nN0] ) printf "Ok doing nothing exiting..\n"
                  exit 6;
                  ;;
              *     ) printf "%b" "Unexpected answer '$answer'!" >&2
                  exit 7;
                  ;;
          esac
      } # end of function choose
  
      # printf "profile = %s \n\n" "$profile"
      ## Query nix-env for generations list
      #IFS=$'\n' nixGens=( $(nix-env --list-generations -p "$profile" | sed 's:^\s*::; s:\s*$::' | tr '\t' ' ' | tr -s ' ') )
      # gave errors replaced by:
      mapfile -t nixGens < <(
        nix-env --list-generations -p "$profile" |
        sed 's:^\s*::; s:\s*$::' |
        tr '\t' ' ' |
        tr -s ' '
      )
      timeNow=$(date +%s)
  
      ## Get info on oldest generation
      IFS=' ' read -r -a oldestGenArr <<< "''${nixGens[0]}"
      oldestGen=''${oldestGenArr[0]}
      oldestDate=''${oldestGenArr[1]}
      printf "%-30s %s\n" "oldest generation:" "$oldestGen"
      #oldestDate=''${nixGens[0]:3:19}
      printf "%-30s %s\n" "oldest generation created:" "$oldestDate"
      oldestTime=$(date -d "$oldestDate" +%s)
      oldestElapsedSecs=$((timeNow-oldestTime))
      oldestElapsedMins=$((oldestElapsedSecs/60))
      oldestElapsedHours=$((oldestElapsedMins/60))
      oldestElapsedDays=$((oldestElapsedHours/24))
      printf "%-30s %s\n" "minutes before now:" "$oldestElapsedMins"
      printf "%-30s %s\n" "hours before now:" "$oldestElapsedHours"
      printf "%-30s %s\n\n" "days before now:" "$oldestElapsedDays"
  
      ## Get info on current generation
      for i in "''${nixGens[@]}"; do
          IFS=' ' read -r -a iGenArr <<< "$i"
          genNumber=''${iGenArr[0]}
          genDate=''${iGenArr[1]}
          if [[ "$i" =~ current ]]; then
              currentGen=$genNumber
              printf "%-30s %s\n" "current generation:" "$currentGen"
              currentDate=$genDate
              printf "%-30s %s\n" "current generation created:" "$currentDate"
              currentTime=$(date -d "$currentDate" +%s)
              currentElapsedSecs=$((timeNow-currentTime))
              currentElapsedMins=$((currentElapsedSecs/60))
              currentElapsedHours=$((currentElapsedMins/60))
              currentElapsedDays=$((currentElapsedHours/24))
              printf "%-30s %s\n" "minutes before now:" "$currentElapsedMins"
              printf "%-30s %s\n" "hours before now:" "$currentElapsedHours"
              printf "%-30s %s\n\n" "days before now:" "$currentElapsedDays"
          fi
      done
  
      ## Compare oldest and current generations
      timeBetweenOldestAndCurrent=$((currentTime-oldestTime))
      elapsedDays=$((timeBetweenOldestAndCurrent/60/60/24))
      generationsDiff=$((currentGen-oldestGen))
  
      ## Figure out what we should do, based on generations and options
      if [[ elapsedDays -le keepDays ]]; then
          printf "All generations are no more than %s days older than current generation. \nOldest gen days difference from current gen: %s \n\n\tNothing to do!\n" "$keepDays" "$elapsedDays"
          exit 4;
      elif [[ generationsDiff -lt keepGens ]]; then
          printf "Oldest generation (%d) is only %d generations behind current (%d). \n\n\t Nothing to do!\n" "$oldestGen" "$generationsDiff" "$currentGen"
          exit 5;
      else
          printf "\tSomething to do...\n"
          declare -a gens
          for i in "''${nixGens[@]}"; do
              IFS=' ' read -r -a iGenArr <<< "$i"
              genNumber=''${iGenArr[0]}
              genDiff=$((currentGen-genNumber))
              genDate=''${iGenArr[1]}
              genTime=$(date -d "$genDate" +%s)
              elapsedSecs=$((timeNow-genTime))
              genDaysOld=$((elapsedSecs/60/60/24))
              if [[ genDaysOld -gt keepDays ]] && [[ genDiff -ge keepGens ]]; then
                  gens["$genNumber"]="$genDate, $genDaysOld day(s) old"
              fi
          done
          printf "\nFound the following generation(s) to delete:\n"
          for K in "''${!gens[@]}"; do
              printf "generation %d \t ''${gens[$K]}\n" "$K"
          done
          printf "\n"
          choose "y" "Do you want to delete these? [Y/n]: "
      fi
  
    '';
  };
}