Banking

transacions_ops.js

const functions = require('firebase-admin')
const admin = require('firebase-admin')
const uuidv1 = require('uuid/v1')

admin.initializeApp()
const db = admin.firestore()

export const execPurchase = functions.https.onCall(async (data, context) => {
  const userId = context.auth.uid
  if (!userId) {
    throw new Error(`Missing Authentication`)
  }
  
  const { itemId, quantity } = data

  const purchaseID = uuidv1()
  const userRef = await db.collection(`users`).doc(userId)
  const itemRef = await db.collection(`items`).doc(itemId)
  const purchaseRef = await db.collection(`purchases`).doc(purchaseID)
    
  // ! check if the
  return db.runTransaction((transaction) => {
    return transaction.get(userRef).then((userDoc) => { // ! lock user data
      // ! get the item information
      const itemDoc = transaction.get(itemRef)
      
      // ! check if user can buy
      const { coins, _id: userId } = userDoc.data()
      const { price, id: itemId, name, quantity: availableQuantity } = itemDoc.data()
      const total = price * quantity
      const canBuy =  total < coins
      if (!canBuy) throw new Error(`Not enough coins`)
      
      // ! check if there are enough quantities
      const enoughQuantity = availableQuantity <= quantity
      if (!enoughQuantity) throw new Error(`Not enough ${name}`)
      
      // ! update collections with new values
      transaction.update(userRef, {
        coins: coins - total 
      })
      
      transaction.update(itemRef, {
        quantity: availableQuantity - quantity
      })
      
      // ! register the purchase
      transaction.set(purchaseRef, {
        user_id: userId,
        item_id: itemId,
        quantity,
        total
      })
      
      // ! we are done! let's execute all the operations
    })
  })
}).then(result => {
  console.log('Transaction success!')
}).catch(err => {
  console.log('Transaction failure:', err);
})