import { pluginName } from './common';
import { parse } from 'graphql/language';
import { execute, ExecutionResult } from 'graphql/execution';
import { getIntrospectionQuery, IntrospectionSchema } from 'graphql/utilities';
import stableStringify from 'fast-json-stable-stringify';
import { GraphQLSchema } from 'graphql/type';
import { createHash } from 'crypto';

export async function generateSchemaHash(
  schema: GraphQLSchema,
): Promise<string> {
  const introspectionQuery = getIntrospectionQuery();
  const documentAST = parse(introspectionQuery);
  const result: ExecutionResult = await execute(schema, documentAST);

  if (!result || !result.data || !result.data.__schema) {
    throw new Error(
      `${pluginName}: Unable to generate server introspection document.`,
    );
  }

  const introspectionSchema: 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 createHash('sha512')
    .update(stringifiedSchema)
    .digest('hex');
}