use-firebase.js

import { reactive, toRefs, computed } from '@vue/composition-api'
import Vue from 'vue'
import firebase from 'firebase/app'
import 'firebase/auth'
import 'firebase/firestore'

const state = Vue.observable({
  loading: true,
  signingIn: false,
  uid: null,
  profile: null,
  account: null,
  initialized: false
})

export const useAuth = () => {
  if (!state.initialized) {
    firebase.auth().onAuthStateChanged(setUser)

    state.initialized = true
  }
  
  async function setUser(user) {
    if (user) {
      state.uid = user.uid
    } else {
      state.uid = null
    }
    state.loading = false
  }
}

export const useDoc = (name) => {
  const { uid } = useAuth()

  const firestore = firebase.firestore()
  const collection = firestore.collection(name)
  
  async function update(id, data) {
    const result = await collection.doc(id).update(data)
    return result
  }
}