class GraphQL::StaticValidation::FragmentSpreadsArePossible

def get_possible_types(type, schema)
  if type.kind.wraps?
    get_possible_types(type.of_type, schema)
  elsif type.kind.object?
    [type]
  elsif type.kind.resolves?
    schema.possible_types(type)
  else
    []
  end
end

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|
      fragment_child_name = context.fragments[frag_spread.node.name].type
      fragment_child = context.schema.types[fragment_child_name]
      validate_fragment_in_scope(frag_spread.parent_type, fragment_child, frag_spread.node, context, frag_spread.path)
    end
  }
end

def validate_fragment_in_scope(parent_type, child_type, node, context, path)
  intersecting_types = get_possible_types(parent_type, context.schema) & get_possible_types(child_type, context.schema)
  if intersecting_types.none?
    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