nix-config/packages/hm-cli.nix

{ ... }:

{
  perSystem =
    { pkgs, ... }:
    {
      packages.hm-cli = pkgs.writeShellScriptBin "hm" ''
        set -e

        HM="${pkgs.lib.getExe pkgs.home-manager}"
        FLAKE_PATH="''${HM_PATH:-$HOME/.config/home-manager}"
        FLAKE_OUTPUT="''${HM_USER:-$(whoami)@$(hostname)}"

        show_usage() {
          cat <<EOF
        Usage: hm <command> [args]

        Commands:
          apply                       Switch to a new generation
          generation list             List all generations
          generation delete ID...     Delete specified generation(s)
          generation rollback         Rollback to the previous generation
          generation switch ID        Switch to the specified generation
          generation cleanup          Delete all but the current generation

        Environment Variables:
          HM_PATH           Override default flake path (~/.config/home-manager)
            Currently set to "''${HM_PATH:-<not set>}"
          HM_USER           Override default user output ("$(whoami)@$(hostname)")
            Currently set to "''${HM_USER:-<not set>}"
        EOF
        }

        if [[ $# -eq 0 ]]; then
          show_usage
          exit 1
        fi

        case "$1" in
          apply)
            "$HM" switch --flake "$FLAKE_PATH#$FLAKE_OUTPUT" -b bkp
            ;;
          generation)
            if [[ $# -lt 2 ]]; then
              echo "Error: generation command requires a subcommand"
              show_usage
              exit 1
            fi

            case "$2" in
              list)
                "$HM" generations
                ;;
              delete)
                if [[ $# -lt 3 ]]; then
                  echo "Error: delete requires at least one generation ID"
                  exit 1
                fi
                shift 2
                "$HM" remove-generations "$@"
                ;;
              rollback)
                PREV_GEN=$("$HM" generations | \
                  sed -n 's/^[[:space:]]*id \([0-9]\+\).*/\1/p' | \
                  head -n 2 | tail -n 1)
                if [[ -z "$PREV_GEN" ]]; then
                  echo "Error: could not determine previous generation (possibly only one generation exists)"
                  exit 1
                fi
                "$HM" switch --flake "$FLAKE_PATH" --switch-generation "$PREV_GEN" -b bkp
                ;;
              switch)
                if [[ $# -ne 3 ]]; then
                  echo "Error: switch requires exactly one generation ID"
                  exit 1
                fi
                "$HM" switch --flake "$FLAKE_PATH" --switch-generation "$3" -b bkp
                ;;
              cleanup)
                CURRENT_GEN=$("$HM" generations | sed -n 's/^.*id \([0-9]\+\) .* (current)$/\1/p')
                if [[ -z "$CURRENT_GEN" ]]; then
                  echo "Error: could not determine current generation"
                  exit 1
                fi
                OLD_GENS=$("$HM" generations | sed -n 's/^.*id \([0-9]\+\) .*/\1/p' | grep -v "^$CURRENT_GEN$")
                if [[ -z "$OLD_GENS" ]]; then
                  echo "No old generations to delete"
                else
                  echo "Deleting generations: $(echo $OLD_GENS | tr '\n' ' ')"
                  echo "$OLD_GENS" | xargs "$HM" remove-generations
                  echo "Cleanup complete. Current generation $CURRENT_GEN preserved."
                fi
                ;;
              *)
                echo "Error: unknown generation subcommand '$2'"
                show_usage
                exit 1
                ;;
            esac
            ;;
          *)
            echo "Error: unknown command '$1'"
            show_usage
            exit 1
            ;;
        esac
      '';
    };
}