module GraphQL::Schema::ReduceTypes

def self.crawl_type(type, type_hash, context_description)
  if type.kind.fields?
    type.all_fields.each do |field|
      reduce_type(field.type, type_hash, "Field #{type.name}.#{field.name}")
      field.arguments.each do |name, argument|
        reduce_type(argument.type, type_hash, "Argument #{name} on #{type.name}.#{field.name}")
      end
    end
  end
  if type.kind.object?
    type.interfaces.each do |interface|
      reduce_type(interface, type_hash, "Interface on #{type.name}")
    end
  end
  if type.kind.union?
    type.possible_types.each do |possible_type|
      reduce_type(possible_type, type_hash, "Possible type for #{type.name}")
    end
  end
  if type.kind.input_object?
    type.arguments.each do |argument_name, argument|
      reduce_type(argument.type, type_hash, "Input field #{type.name}.#{argument_name}")
    end
  end
end

def self.reduce(types)
  type_map = GraphQL::Schema::TypeMap.new
  types.each do |type|
    reduce_type(type, type_map, type.name)
  end
  type_map
end

def self.reduce_type(type, type_hash, context_description)
  if !type.is_a?(GraphQL::BaseType)
    message = "#{context_description} has an invalid type: must be an instance of GraphQL::BaseType, not #{type.class.inspect} (#{type.inspect})"
    raise GraphQL::Schema::InvalidTypeError.new(message)
  end
  type = type.unwrap
  # Don't re-visit a type
  if !type_hash.fetch(type.name, nil).equal?(type)
    validate_type(type, context_description)
    type_hash[type.name] = type
    crawl_type(type, type_hash, context_description)
  end
end

def self.validate_type(type, context_description)
  error_message = GraphQL::Schema::Validation.validate(type)
  if error_message
    raise GraphQL::Schema::InvalidTypeError.new("#{context_description} is invalid: #{error_message}")
  end
end