apollo-fetch.ts

import {
  FetchResult,
  RequestAndOptions,
  ResponseAndOptions,
  RequestsAndOptions,
  AfterwareInterface,
  MiddlewareInterface,
  BatchAfterwareInterface,
  BatchMiddlewareInterface,
  FetchOptions,
  ApolloFetch,
  ParsedResponse,
  GraphQLRequest,
  FetchError,
  BatchError,
} from './types';
import 'cross-fetch/polyfill';

type WareStack =
  | MiddlewareInterface[]
  | BatchMiddlewareInterface[]
  | AfterwareInterface[]
  | BatchAfterwareInterface[];

function buildWareStack<M>(funcs: WareStack, modifiedObject: M, resolve) {
  const next = () => {
    if (funcs.length > 0) {
      const f = funcs.shift();
      if (f) {
        f.apply(this, [modifiedObject, next]);
      }
    } else {
      resolve(modifiedObject);
    }
  };
  next();
}

export function constructDefaultOptions(
  requestOrRequests: GraphQLRequest | GraphQLRequest[],
  options: RequestInit,
): RequestInit {
  let body;
  try {
    body = JSON.stringify(requestOrRequests);
  } catch (e) {
    throw new Error(
      `Network request failed. Payload is not serializable: ${e.message}`,
    );
  }

  return {
    body,
    method: 'POST',
    ...options,
    headers: {
      Accept: '*/*',
      'Content-Type': 'application/json',
      ...options.headers || [],
    },
  };
}

function throwHttpError(response, error) {
  let httpError;
  if (response && response.status >= 300) {
    httpError = new Error(
      `Network request failed with status ${response.status} - "${response.statusText}"`,
    );
  } else {
    httpError = new Error(`Network request failed to return valid JSON`);
  }
  (httpError as any).response = response;
  (httpError as any).parseError = error;

  throw httpError as FetchError;
}

function throwBatchError(response) {
  let httpError = new Error(`A batched Operation of responses for `);
  (httpError as any).response = response;

  throw httpError as BatchError;
}

export function createApolloFetch(params: FetchOptions = {}): ApolloFetch {
  const { constructOptions, customFetch } = params;

  const _uri = params.uri || '/graphql';
  const middlewares = [];
  const batchedMiddlewares = [];
  const afterwares = [];
  const batchedAfterwares = [];

  const applyMiddlewares = (
    requestAndOptions: RequestAndOptions | RequestsAndOptions,
    batched: boolean,
  ): Promise<RequestAndOptions | RequestsAndOptions> => {
    return new Promise((resolve, reject) => {
      if (batched) {
        buildWareStack([...batchedMiddlewares], requestAndOptions, resolve);
      } else {
        buildWareStack([...middlewares], requestAndOptions, resolve);
      }
    });
  };

  const applyAfterwares = (
    responseObject: ResponseAndOptions,
    batched: boolean,
  ): Promise<ResponseAndOptions> => {
    return new Promise((resolve, reject) => {
      if (batched) {
        buildWareStack([...batchedAfterwares], responseObject, resolve);
      } else {
        buildWareStack([...afterwares], responseObject, resolve);
      }
    });
  };

  const apolloFetch = function(
    request: GraphQLRequest | GraphQLRequest[],
  ): Promise<FetchResult | FetchResult[]> {
    let options = {};
    let parseError;

    const batched = Array.isArray(request);

    const requestObject = <RequestAndOptions | RequestsAndOptions>(batched
      ? {
          requests: request,
          options,
        }
      : {
          request,
          options,
        });

    return applyMiddlewares(requestObject, batched)
      .then(reqOpts => {
        const construct = constructOptions || constructDefaultOptions;
        const requestOrRequests =
          (<RequestAndOptions>reqOpts).request ||
          (<RequestsAndOptions>reqOpts).requests;
        return construct(requestOrRequests, reqOpts.options);
      })
      .then(opts => {
        options = { ...opts };
        return (customFetch || fetch)(_uri, options);
      })
      .then(
        response =>
          response.text().then(raw => {
            try {
              const parsed = JSON.parse(raw);
              (response as ParsedResponse).raw = raw;
              (response as ParsedResponse).parsed = parsed;
              return <ParsedResponse>response;
            } catch (e) {
              parseError = e;

              //pass parsed raw response onto afterware
              (response as ParsedResponse).raw = raw;
              return <ParsedResponse>response;
            }
          }),
        //.catch() this should never happen: https://developer.mozilla.org/en-US/docs/Web/API/Body/text
      )
      .then(response =>
        applyAfterwares(
          {
            response,
            options,
          },
          batched,
        ),
      )
      .then(({ response }) => {
        if (response.parsed) {
          if (batched) {
            if (Array.isArray(response.parsed)) {
              return response.parsed as FetchResult[];
            } else {
              throwBatchError(response);
            }
          } else {
            return { ...response.parsed };
          }
        } else {
          throwHttpError(response, parseError);
        }
      });
  };

  (apolloFetch as any).use = (middleware: MiddlewareInterface) => {
    if (typeof middleware === 'function') {
      middlewares.push(middleware);
    } else {
      throw new Error('Middleware must be a function');
    }

    return apolloFetch;
  };

  (apolloFetch as any).useAfter = (afterware: AfterwareInterface) => {
    if (typeof afterware === 'function') {
      afterwares.push(afterware);
    } else {
      throw new Error('Afterware must be a function');
    }

    return apolloFetch;
  };

  (apolloFetch as any).batchUse = (middleware: BatchMiddlewareInterface) => {
    if (typeof middleware === 'function') {
      batchedMiddlewares.push(middleware);
    } else {
      throw new Error('Middleware must be a function');
    }

    return apolloFetch;
  };

  (apolloFetch as any).batchUseAfter = (afterware: BatchAfterwareInterface) => {
    if (typeof afterware === 'function') {
      batchedAfterwares.push(afterware);
    } else {
      throw new Error('Afterware must be a function');
    }

    return apolloFetch;
  };

  return apolloFetch as ApolloFetch;
}