{ config, lib, pkgs, ... }:

with lib;
{
  options = {
    environment.binbash.enable = mkOption {
      default = true;
      type = types.bool;
      description = ''
        Include a /bin/bash in the system.
      '';
    };
    environment.binbash.bash = mkOption {
        type = types.package;
        default = pkgs.bashInteractive;
        defaultText = literalExpression "pkgs.bashInteractive";
        example = literalExpression "pkgs.bash";
        description = lib.mdDoc ''
          The bash implementation that will be present in
          `/bin/bash` after enabling this option.
        '';
      };
  };

  config = {
    system.activationScripts.binbash = if config.environment.binbash.enable
      then ''
        mkdir -m 0755 -p /bin
        ln -sfn ${config.environment.binbash.bash}/bin/bash /bin/.bash.tmp
        mv /bin/.bash.tmp /bin/bash # atomically replace /usr/bin/env
      ''
      else ''
        rm -f /bin/bash
      '';
  };
}