firebase-query.js

import { LRUCache } from './lru-cache.js';

const FirebaseQueryAction = {
  snapshotReceived: 'FIREBASE_QUERY_SNAPSHOT_RECEIVED',
  created: 'FIREBASE_QUERY_CREATED'
};

const FirebaseQueryActionCreatorCache = (maxRealtimeQueries = 10) => {
  const cache = new LRUCache(
      maxRealtimeQueries,
      ({ query, unsubscribe }) => unsubscribe());
  const db = firebase.firestore();

  return (key, queryFactory) => dispatch => {
    const existingQuery = cache.get(key);

    if (existingQuery == null) {
      const query = queryFactory(db);
      const unsubscribe = query.onSnapshot(querySnapshot => {
        dispatch({
          type: FirebaseQueryAction.snapshotReceived,
          payload: { key, querySnapshot }
        });
      });

      cache.set(cacheKey, { query, unsubscribe });

      dispatch({
        type: FirebaseQueryAction.created,
        payload: { key }
      });
    }
  };
};


const FirebaseQueriesReducer = (
    state = {},
    action) => {
  switch(action.type) {
    case FirebaseQueryAction.created:
    case FirebaseQueryAction.snapshotReceived:
      const { key } = action.payload;
      return {
        ...state,
        [key]: FirebaseQueryReducer(state[key], action)
      };
    default:
      return state;
  }
}


const FirebaseQueryReducer = (
    state = { pending: true, items: [] },
    action) => {
  switch(action.type) {
    default:
    case FirebaseQueryAction.created:
      return state;
    case FirebaseQueryAction.snapshotReceived:
      const { querySnapshot } = action.payload;
      const { items } = state;

      querySnapshot.docChanges.forEach(change => {
        switch (change.type) {
          case 'added':
            items.splice(change.newIndex, 0, change.doc.data());
            break;
          case 'changed':
            items.splice(change.oldIndex, 1);
            items.splice(change.newIndex, 0, change.doc.data());
            break;
          case 'removed':
            items.splice(change.oldIndex, 1);
            break;
        }
      });

      return { pending: false, items };
  }
}

export {
  FirebaseQueryAction,
  FirebaseQueriesReducer,
  FirebaseQueryActionCreatorCache
};