import { ExecutionResult, buildClientSchema, getIntrospectionQuery } from 'graphql';
import { GraphQLSchemaValidationOptions } from 'graphql/type/schema';
import fetch from 'isomorphic-unfetch';
import qs from 'qs';

export interface SchemaFetcher {
  (query: string, fetchImpl: typeof fetch, qsImpl: typeof qs): Promise<ExecutionResult>;
}

export async function fetchSchema({
  endpoint,
  usePost = false,
  headers,
  options,
}: {
  endpoint: string;
  usePost: boolean;
  headers?: Record<string, string>;
  options?: GraphQLSchemaValidationOptions;
}) {
  const response = await fetch(
    usePost ? endpoint : `${endpoint}?${qs.stringify({ query: getIntrospectionQuery() })}`,
    usePost
      ? {
          method: usePost ? 'POST' : 'GET',
          body: JSON.stringify({ query: getIntrospectionQuery() }),
          headers: { ...headers, 'Content-Type': 'application/json' },
        }
      : {
          headers,
        },
  );
  if (!response.ok) {
    throw new Error('introspection query was not successful, ' + response.statusText);
  }

  const result = await response.json().catch((e) => {
    const contentType = response.headers.get('Content-Type');
    console.log(`content type is ${contentType}`);
    throw new Error(
      `endpoint '${endpoint}' did not return valid json, check that your endpoint points to a valid graphql api`,
    );
  });
  if (!result.data) {
    throw new Error('introspection request did not receive a valid response');
  }

  // console.log(result.data)
  // console.log(JSON.stringify(result.data, null, 4))

  return buildClientSchema(result.data, options);
}

export async function customFetchSchema(fetcher: SchemaFetcher, options?: GraphQLSchemaValidationOptions) {
  const result = await fetcher(getIntrospectionQuery(), fetch, qs);

  if (!result.data) {
    throw new Error('introspection request did not receive a valid response');
  }

  return buildClientSchema(result.data as any, options);
}