import { parse } from 'graphql/language';
import { execute, ExecutionResult } from 'graphql/execution';
import { getIntrospectionQuery, IntrospectionQuery } from 'graphql/utilities';
import stableStringify from 'fast-json-stable-stringify';
import type { GraphQLSchema } from 'graphql/type';
import createSHA from './createSHA';
import type { SchemaHash } from 'apollo-server-types';

/*
 * This function returns a not particularly stable schema hash derived from a
 * GraphQLSchema object. It works by running the `graphql-js` default
 * introspection query against the schema and taking a SHA of a JSON encoding of
 * the result. It is dependent on the precise introspection query returned by
 * `graphql-js` and some of the details of how that library returns its data, so
 * upgrading `graphql-js` can change its value. It was created for use in
 * apollo-server-plugin-operation-registry (now @apollo/server-plugin-operation-registry) * but it is no longer used there. It is *not* the same as the hash used in
 * schema and usage reporting, which is just a hash of the schema SDL document.
 *
 * For backwards-compatibility reasons, it is still calculated and passed to all
 * plugin hooks, but it is not a good idea to use it for anything.
 */
export function generateSchemaHash(schema: GraphQLSchema): SchemaHash {
  const introspectionQuery = getIntrospectionQuery();
  const document = parse(introspectionQuery);
  const result = execute({
    schema,
    document,
  }) as ExecutionResult<IntrospectionQuery>;

  // If the execution of an introspection query results in a then-able, it
  // indicates that one or more of its resolvers is behaving in an asynchronous
  // manner.  This is not the expected behavior of a introspection query
  // which does not have any asynchronous resolvers.
  if (
    result &&
    typeof (result as PromiseLike<typeof result>).then === 'function'
  ) {
    throw new Error(
      [
        'The introspection query is resolving asynchronously; execution of an introspection query is not expected to return a `Promise`.',
        '',
        'Wrapped type resolvers should maintain the existing execution dynamics of the resolvers they wrap (i.e. async vs sync) or introspection types should be excluded from wrapping by checking them with `graphql/type`s, `isIntrospectionType` predicate function prior to wrapping.',
      ].join('\n'),
    );
  }

  if (!result || !result.data || !result.data.__schema) {
    throw new Error('Unable to generate server introspection document.');
  }

  const introspectionSchema = result.data.__schema;

  // It's important that we perform a deterministic stringification here
  // since, depending on changes in the underlying `graphql-js` execution
  // layer, varying orders of the properties in the introspection
  const stringifiedSchema = stableStringify(introspectionSchema);

  return createSHA('sha512')
    .update(stringifiedSchema)
    .digest('hex') as SchemaHash;
}