How to use the graphql-tools.addSchemaLevelResolveFunction function in graphql-tools

? await plugin.middleware({ config })
                : plugin.middleware;
        if (Array.isArray(middleware)) {
            registeredMiddleware.push(...middleware);
        } else {
            registeredMiddleware.push(middleware);
        }
    }

    config.middleware && registeredMiddleware.push(config.middleware);

    if (registeredMiddleware.length) {
        schema = applyMiddleware(schema, ...registeredMiddleware);
    }

    addSchemaLevelResolveFunction(schema, async (root, args, context, info) => {
        // Make sure we do not block this resolver from processing subsequent requests!
        // This is something that is baked into the graphql-tools and cannot be avoided another way.
        delete info.operation["__runAtMostOnce"];

        // Process `graphql-context` plugins
        const ctxPlugins = getPlugins("graphql-context");

        for (let i = 0; i < ctxPlugins.length; i++) {
            const ctxPlugin = ctxPlugins[i];
            if (typeof ctxPlugin.preApply === "function") {
                await ctxPlugin.preApply(context);
            }
        }

        for (let i = 0; i < ctxPlugins.length; i++) {
            const ctxPlugin = ctxPlugins[i];

const middleware =
            typeof plugin.middleware === "function"
                ? await plugin.middleware({ plugins })
                : plugin.middleware;
        if (Array.isArray(middleware)) {
            registeredMiddleware.push(...middleware);
        } else {
            registeredMiddleware.push(middleware);
        }
    }

    if (registeredMiddleware.length) {
        schema = applyMiddleware(schema, ...registeredMiddleware);
    }

    addSchemaLevelResolveFunction(schema, async (root, args, context, info) => {
        // Make sure we do not block this resolver from processing subsequent requests!
        // This is something that is baked into the graphql-tools and cannot be avoided another way.
        delete info.operation["__runAtMostOnce"];

        // Process `graphql-context` plugins
        const ctxPlugins = plugins.byType("graphql-context");
        for (let i = 0; i < ctxPlugins.length; i++) {
            if (typeof ctxPlugins[i].preApply === "function") {
                await ctxPlugins[i].preApply(context);
            }
        }

        for (let i = 0; i < ctxPlugins.length; i++) {
            if (typeof ctxPlugins[i].apply === "function") {
                await ctxPlugins[i].apply(context);
            }

? await plugin.middleware({ config })
                : plugin.middleware;
        if (Array.isArray(middleware)) {
            registeredMiddleware.push(...middleware);
        } else {
            registeredMiddleware.push(middleware);
        }
    }

    config.middleware && registeredMiddleware.push(config.middleware);

    if (registeredMiddleware.length) {
        schema = applyMiddleware(schema, ...registeredMiddleware);
    }

    addSchemaLevelResolveFunction(schema, async (root, args, context, info) => {
        // Make sure we do not block this resolver from processing subsequent requests!
        // This is something that is baked into the graphql-tools and cannot be avoided another way.
        delete info.operation["__runAtMostOnce"];

        // Process `graphql-context` plugins
        const ctxPlugins = getPlugins("graphql-context");
        for (let i = 0; i < ctxPlugins.length; i++) {
            if (typeof ctxPlugins[i].preApply === "function") {
                await ctxPlugins[i].preApply(context);
            }
        }

        for (let i = 0; i < ctxPlugins.length; i++) {
            if (typeof ctxPlugins[i].apply === "function") {
                await ctxPlugins[i].apply(context);
            }

Notification,
    Meta,
    Invoice,
    Search,
  ],
  resolvers,
  schemaDirectives: IS_PROD
    ? {
        rateLimit,
      }
    : {},
});

if (process.env.REACT_APP_MAINTENANCE_MODE === 'enabled') {
  console.error('\n\n⚠️ ----MAINTENANCE MODE ENABLED----⚠️\n\n');
  addSchemaLevelResolveFunction(schema, () => {
    throw new UserError(
      "We're currently undergoing planned maintenance. We'll be back soon, please check https://twitter.com/withspectrum for ongoing updates!"
    );
  });
}

module.exports = schema;

addSchemaResolvers: rootResolveFunction =>
        addSchemaLevelResolveFunction(this.schema, rootResolveFunction),
      addDirectivesResolvers: directivesResolvers =>

.forEach(({ plugin, schemaLevelResolveFunction }) => {
    debug(`added schemaLevelResolveFunction from plugin '${plugin.name}'`);

    addSchemaLevelResolveFunction(schema, schemaLevelResolveFunction);
  });