class GraphQL::StaticValidation::FragmentSpreadsArePossible

def validate(context)
  context.visitor[GraphQL::Language::Nodes::InlineFragment] << ->(node, parent) {
    fragment_parent = context.object_types[-2]
    fragment_child = context.object_types.last
    if fragment_child
      validate_fragment_in_scope(fragment_parent, fragment_child, node, context, context.path)
    end
  }
  spreads_to_validate = []
  context.visitor[GraphQL::Language::Nodes::FragmentSpread] << ->(node, parent) {
    fragment_parent = context.object_types.last
    spreads_to_validate << FragmentSpread.new(node: node, parent_type: fragment_parent, path: context.path)
  }
  context.visitor[GraphQL::Language::Nodes::Document].leave << ->(doc_node, parent) {
    spreads_to_validate.each do |frag_spread|
      frag_node = context.fragments[frag_spread.node.name]
      if frag_node
        fragment_child_name = frag_node.type.name
        fragment_child = context.warden.get_type(fragment_child_name)
        # Might be non-existent type name
        if fragment_child
          validate_fragment_in_scope(frag_spread.parent_type, fragment_child, frag_spread.node, context, frag_spread.path)
        end
      end
    end
  }
end

def validate_fragment_in_scope(parent_type, child_type, node, context, path)
  if !child_type.kind.fields?
    # It's not a valid fragment type, this error was handled someplace else
    return
  end
  parent_types = context.warden.possible_types(parent_type.unwrap)
  child_types = context.warden.possible_types(child_type.unwrap)
  if child_types.none? { |c| parent_types.include?(c) }
    name = node.respond_to?(:name) ? " #{node.name}" : ""
    context.errors << message("Fragment#{name} on #{child_type.name} can't be spread inside #{parent_type.name}", node, path: path)
  end
end