# The abstract model visitor template.
#
# Specific visitor must implement the `visit` method to perform the work.
abstract class ModelVisitor

	# Visit the entity `e`.
	#
	# This method setups `current_entity` and call `visit`.
	# If `e` is null, nothing is done.
	fun enter_visit(e: nullable MEntity) do
		if e == null then return
		if not accept_mentity(e) then return
		var old_entity = current_entity
		current_entity = e
		visit(e)
		current_entity = old_entity
	end

	# The current visited entity
	var current_entity: nullable MEntity = null

	# Method to define in specific visitor.
	#
	# It should not be called directly but used by `enter_visit`
	protected fun visit(e: MEntity) is abstract

	# Filters to apply when visiting the model.
	#
	# See ModelFilters for configuration.
	var filter: ModelFilter is lazy, writable, optional do
		return new ModelFilter(
			min_visibility = protected_visibility,
			accept_fictive = false,
			accept_test = false,
			accept_example = false,
			accept_redef = true,
			accept_extern = true,
			accept_attribute = true,
			accept_empty_doc = true
		)
	end

	# Should we accept this `mentity` from the view?
	#
	# If no `override_filter` is passed then use `self.filter`.
	fun accept_mentity(mentity: MEntity, override_filter: nullable ModelFilter): Bool do
		if override_filter != null then
			return override_filter.accept_mentity(mentity)
		end
		return filter.accept_mentity(mentity)
	end
end