import { getDirective, MapperKind, mapSchema } from '@graphql-tools/utils';
import { defaultFieldResolver, GraphQLSchema } from 'graphql';

export function upperDirectiveTransformer(
  schema: GraphQLSchema,
  directiveName: string
) {
  return mapSchema(schema, {
    [MapperKind.OBJECT_FIELD]: (fieldConfig) => {
      const upperDirective = getDirective(
        schema,
        fieldConfig,
        directiveName
      )?.[0];

      if (upperDirective) {
        const { resolve = defaultFieldResolver } = fieldConfig;

        // Replace the original resolver with a function that *first* calls
        // the original resolver, then converts its result to upper case
        fieldConfig.resolve = async function (source, args, context, info) {
          const result = await resolve(source, args, context, info);
          if (typeof result === 'string') {
            return result.toUpperCase();
          }
          return result;
        };
        return fieldConfig;
      }
    },
  });
}

GraphQLModule.forRoot({
  // ...
  transformSchema: (schema) => upperDirectiveTransformer(schema, 'upper'),
});

@Directive('@upper')
@Field()
title: string;

@Directive('@deprecated(reason: "This query will be removed in the next version")')
@Query(() => Author, { name: 'author' })
async getAuthor(@Args({ name: 'id', type: () => Int }) id: number) {
  return this.authorsService.findOneById(id);
}

GraphQLModule.forRoot({
  // ...,
  transformSchema: schema => upperDirectiveTransformer(schema, 'upper'),
  buildSchemaOptions: {
    directives: [
      new GraphQLDirective({
        name: 'upper',
        locations: [DirectiveLocation.FIELD_DEFINITION],
      }),
    ],
  },
}),