db.js

const admin = require('firebase-admin');
var db;

module.exports.addItem = function(table, id, object) {
    if (!db) {
        db = connectToDb();
    }

    db.collection(table).doc(id).set(object);
}

// addItem('config', 'test', {value: 'test'});

module.exports.fetchItem = async function(table, id) {
    if (!db) {
        db = connectToDb();
    }
    var data;
    await db.collection(table).get()
        .then((snapshot) => {
            snapshot.forEach((doc) => {
                if (doc.id === id) {
                    data = doc.data();
                }
            });
        })
        .catch((err) => {
            console.log('Error getting documents', err);
        })
    return data;
}

// fetchItem('config', 'test').then(thing => {
//     console.log(thing);
// });

module.exports.deleteItem = function(table, id) {
    if (!db) {
        db = connectToDb();
    }
    db.collection(table).doc(id).delete();
}

// deleteItem('config', 'test');

module.exports.updateItem = function(table, id, newValue) {
    if (!db) {
        db = connectToDb();
    }
    let docRef = db.collection(table).doc(id);
    let updateSingle = docRef.update(newValue);
}

module.exports.fetchAllItems = async function(table) {
    if (!db) {
        db = connectToDb();
    }
    var data = [];
    await db.collection(table).get()
        .then((snapshot) => {
            snapshot.forEach((doc) => {
                data.push(doc);
            });
        })
        .catch((err) => {
            console.log('Error getting documents', err);
        })
    return data;
}

function connectToDb() {

    admin.initializeApp({
        credential: admin.credential.cert(JSON.parse(process.env.DB_KEY))
    });
    return admin.firestore();
}

//updateItem('config', 'test', {value: 'test2'});