export const FIREBASE = Symbol('FIREBASE');

// Middleware constructor
export default firebase => {
  // Init auth providers
  const providers = {
    fb: new firebase.auth.FacebookAuthProvider(),
    google: new firebase.auth.GoogleAuthProvider()
  };

  // This is the basic middleware pattern
  return ({ dispatch }) => next => action => {
    const firebaseAction = action[FIREBASE];

    // Let the action pass if it is not a 'firebase' action
    if (typeof firebaseAction === "undefined") {
      return next(action);
    }

    const { withFirebase, types, callBack } = firebaseAction;
    const [request, success, failure] = types;

    const promise = withFirebase(firebase, providers);
    dispatch({
      type: request,
      payload: {}
    });

    // This is an async immediately invoked function
    (async () => {
      const [error, response] = await handle(promise);

      if (error) {
        return dispatch({
          type: failure,
          payload: error
        })
      }

      if (response) {
        dispatch({
          type: success,
          payload: response
          });
        callBack && callBack();
      }
    })();
  };
};

// More on this explained below
function handle(promise) {
  return promise.then(res => [null, res]).catch(err => [err, null]);
}