module UniverseCompiler
  module Entity

    module Inheritance

      extend UniverseCompiler::Entity::FieldBinder

      field_accessor :extends
      attr_reader :compiled

      def apply_inheritance
        return unless compiled.nil?
        unless extends.nil?
          valid_for_inheritance? raise_error: true
          @fields = fields_inheritance_result
        end
      ensure
        @compiled = true
      end

      def valid_for_inheritance?(raise_error: false)
        is_valid = true
        unless extends.nil?
          is_valid = false
          if extends.respond_to? :type and extends.respond_to? :name
            if extends.respond_to? :fields or extends.is_a? UniverseCompiler::Entity::Reference
              is_valid = self.type == extends.type
            end
          end
        end
        return true if is_valid
        false_or_raise "Invalid entity '#{to_composite_key}' ! Inheritance is invalid !", raise_error: raise_error
      end

      private

      def fields_inheritance_result
        stack = inheritance_stack(self).reverse
        return stack.first if stack.size == 1
        merge_engine = SuperStack::Manager.new
        merge_engine.merge_policy = SuperStack::MergePolicies::InheritanceMergePolicy
        stack.each { |entity| merge_engine << entity.fields.dup }
        merge_engine[]
      end

      def inheritance_stack(entity, stack=[], visited=[])
        if visited.include? entity
          display_as_path = display_path(*visited.map(&:to_composite_key), entity.to_composite_key)
          raise UniverseCompiler::Error, "Circular reference detected for '#{to_composite_key}' (#{display_as_path}) !"
        end
        visited << entity
        stack << entity
        return stack unless entity.extends
        parent = entity.extends
        if parent.nil?
          display_as_path = display_path(*visited.map(&:to_composite_key), entity.extends.to_composite_key)
          err_msg = "Invalid inheritance defined in '#{entity.to_composite_key}' extending '#{entity.to_composite_key}' (#{display_as_path}) !"
          raise UniverseCompiler::Error, err_msg
        end
        stack = inheritance_stack parent, stack, visited
        stack
      end


      def inherited_fields_stack(entity, stack=[], visited=[])
        if visited.include? entity
          raise UniverseCompiler::Error, "Circular reference detected for '#{self.to_composite_key}' (#{display_path(*visited.map(&:to_composite_key), entity.to_composite_key)}) !"
        end
        visited << entity
        stack << entity.fields
        return stack unless entity.extends
        parent = entity.extends
        if parent.nil?
          raise UniverseCompiler::Error, "Invalid inheritance defined in '#{entity.to_composite_key}' extending '#{entity.to_composite_key}' (#{display_path(*visited.map(&:composite_key), entity.extends.to_composite_key)}) !"
        end
        stack = inherited_fields_stack parent, stack, visited
        stack
      end

      def display_path(*names)
        names.join ' -> '
      end

    end

  end
end