API middleware

api.js

const API         = 'API';
const API_STARTED = 'API_STARTED';
const API_ERROR   = 'API_ERROR';
const API_DONE    = 'API_DONE';
const CANCEL_API  = 'CANCEL_API';

const API_ROOT = 'https://s3.amazonaws.com/500tech-shared/';


const apiAction = {
  type: API,
  request: {
    url: 'users.json',
    method: 'GET'
  },
  response: {
    success: 'SET_USERS',
    error:   'NONE',
    pending: 'NONE'
  },
  meta: {
    skipAuth: false
  }
};

const canceled = {};

const apiMiddleware = ({ dispatch, getState }) => next => action => {

  function setupRequest({ url, method = 'GET', body }) {
    const { accessToken } = getState().currentUser || {};
    const { skipAuth } = action.meta || {};
    const { pending } = action.response;
    const params = { method };

    // Notify system that an API request has started
    dispatch({ type: pending ? pending : API_STARTED });

    if (!skipAuth && accessToken) {
      params.headers = { accessToken }
    }

    if (method === 'POST') {
      params.body = JSON.stringify(body);
    }

    return fetch(API_ROOT + url, params);
  }

  const checkStatus = response => {
    if (response.status >= 200 && response.status < 300) {
      return response;
    } else {
      var error = new Error(response.statusText);
      error.response = response;
      throw error;
    }
  };

  const handleResponse = data => {
    const { success } = action.response;
    const { cancelable } = action.meta || {};

    if (cancelable && canceled[cancelable]) {
      return;
    }

    dispatch({ type: success, payload: data });

    dispatch({ type: API_DONE });
  };

  const handleError = error => {
    const errorAction = action.response.error;
    const { cancelable } = action.meta || {};

    if (cancelable && canceled[cancelable]) {
      return;
    }

    if (errorAction) {
      dispatch({type: errorAction, error});
    }

    dispatch({ type: API_ERROR, error });
  };

  switch (action.type) {
    case API:
      setupRequest(action.request)
        .then(checkStatus)
        .then(response => response.json())
        .then(handleResponse)
        .catch(handleError);
      break;

    case CANCEL_API:
      canceled[action.id] = true;
      setTimeout(() => delete canceled[action.id], 5000);
      break;
  }

  return next(action);
};

export default apiMiddleware;