discourse/app/services/group_action_logger.rb

class GroupActionLogger

  def initialize(acting_user, group)
    @acting_user = acting_user
    @group = group
  end

  def log_make_user_group_owner(target_user)
    can_edit?

    GroupHistory.create!(default_params.merge(
      action: GroupHistory.actions[:make_user_group_owner],
      target_user: target_user
    ))
  end

  def log_remove_user_as_group_owner(target_user)
    can_edit?

    GroupHistory.create!(default_params.merge(
      action: GroupHistory.actions[:remove_user_as_group_owner],
      target_user: target_user
    ))
  end

  def log_add_user_to_group(target_user)
    (target_user == @acting_user && @group.public_admission) || can_edit?

    GroupHistory.create!(default_params.merge(
      action: GroupHistory.actions[:add_user_to_group],
      target_user: target_user
    ))
  end

  def log_remove_user_from_group(target_user)
    (target_user == @acting_user && @group.public_exit) || can_edit?

    GroupHistory.create!(default_params.merge(
      action: GroupHistory.actions[:remove_user_from_group],
      target_user: target_user
    ))
  end

  def log_change_group_settings
    can_edit?

    @group.previous_changes.except(*excluded_attributes).each do |attribute_name, value|
      next if value[0].blank? && value[1].blank?

      GroupHistory.create!(default_params.merge(
        action: GroupHistory.actions[:change_group_setting],
        subject: attribute_name,
        prev_value: value[0],
        new_value: value[1]
      ))
    end
  end

  private

  def excluded_attributes
    [
      :bio_cooked,
      :updated_at,
      :created_at,
      :user_count
    ]
  end

  def default_params
    { group: @group, acting_user: @acting_user }
  end

  def can_edit?
    raise Discourse::InvalidParameters.new unless Guardian.new(@acting_user).can_log_group_changes?(@group)
  end

end