module ViewComponent::Slotable

def slot(slot_name, **args, &block)
  # Raise ArgumentError if `slot` doesn't exist
  unless slots.key?(slot_name)
    raise ArgumentError.new "Unknown slot '#{slot_name}' - expected one of '#{slots.keys}'"
  end
  slot = slots[slot_name]
  # The class name of the Slot, such as Header
  slot_class = self.class.const_get(slot[:class_name])
  unless slot_class <= ViewComponent::Slot
    raise ArgumentError.new "#{slot[:class_name]} must inherit from ViewComponent::Slot"
  end
  # Instantiate Slot class, accommodating Slots that don't accept arguments
  slot_instance = args.present? ? slot_class.new(**args) : slot_class.new
  # Capture block and assign to slot_instance#content
  slot_instance.content = view_context.capture(&block).to_s.strip.html_safe if block
  if slot[:collection]
    # Initialize instance variable as an empty array
    # if slot is a collection and has yet to be initialized
    unless instance_variable_defined?(slot[:instance_variable_name])
      instance_variable_set(slot[:instance_variable_name], [])
    end
    # Append Slot instance to collection accessor Array
    instance_variable_get(slot[:instance_variable_name]) << slot_instance
  else
    # Assign the Slot instance to the slot accessor
    instance_variable_set(slot[:instance_variable_name], slot_instance)
  end
  # Return nil, as this method shouldn't output anything to the view itself.
  nil
end