// @flow
import type { Plugin } from "../SchemaBuilder";

function isValidMutation(Mutation) {
  try {
    if (!Mutation) {
      return false;
    }
    if (Object.keys(Mutation.getFields()).length === 0) {
      return false;
    }
  } catch (e) {
    return false;
  }
  return true;
}

export default (async function MutationPlugin(builder) {
  builder.hook(
    "GraphQLSchema",
    (schema: {}, build) => {
      const {
        newWithHooks,
        extend,
        graphql: { GraphQLObjectType },
        inflection,
      } = build;
      const Mutation = newWithHooks(
        GraphQLObjectType,
        {
          name: inflection.builtin("Mutation"),
          description: build.wrapDescription(
            "The root mutation type which contains root level fields which mutate data.",
            "type"
          ),
        },
        {
          __origin: `graphile-build built-in (root mutation type)`,
          isRootMutation: true,
        },
        true
      );
      if (isValidMutation(Mutation)) {
        return extend(
          schema,
          {
            mutation: Mutation,
          },
          "Adding mutation type to schema"
        );
      } else {
        return schema;
      }
    },
    ["Mutation"],
    [],
    ["Query"]
  );
}: Plugin);