add poc for firestore

src/db.js

@@ -1,15 +1,51 @@
 (() => {
 	const FAUX_DELAY = 1;
+
+	var db;
+	var dbPromise;
+
+	async function getDb() {
+		if (dbPromise) {
+			return dbPromise;
+		}
+		dbPromise = new Promise((resolve, reject) => {
+			if (db) {
+				return resolve(db);
+			}
+			firebase
+				.firestore()
+				.enablePersistence()
+				.then(function() {
+					// Initialize Cloud Firestore through firebase
+					db = firebase.firestore();
+					console.log('firebase db ready', db);
+					resolve(db);
+				})
+				.catch(function(err) {
+					reject(err.code);
+					if (err.code === 'failed-precondition') {
+						// Multiple tabs open, persistence can only be enabled
+						// in one tab at a a time.
+						// ...
+					} else if (err.code === 'unimplemented') {
+						// The current browser does not support all of the
+						// features required to enable persistence
+						// ...
+					}
+				});
+		});
+		return dbPromise;
+	}
+
 	var local = {
 		get: (obj, cb) => {
+			const retVal = {};
 			if (typeof obj === 'string') {
-				const retVal = {};
 				retVal[obj] = JSON.parse(window.localStorage.getItem(obj));
 				setTimeout(() => cb(retVal), FAUX_DELAY);
 			} else {
-				const retVal = {};
 				Object.keys(obj).forEach(key => {
-					let val = window.localStorage.getItem(key);
+					const val = window.localStorage.getItem(key);
 					retVal[key] =
 						val === undefined || val === null ? obj[key] : JSON.parse(val);
 				});
@@ -21,11 +57,14 @@
 				window.localStorage.setItem(key, JSON.stringify(obj[key]));
 			});
 			setTimeout(() => {
-				if (cb) cb();
+				if (cb) {
+					cb();
+				}
 			}, FAUX_DELAY);
 		}
 	};
 	window.db = {
+		getDb,
 		local: chrome && chrome.storage ? chrome.storage.local : local,
 		sync: chrome && chrome.storage ? chrome.storage.sync : local
 	};