zingcash.js

const useZingCash = (userId, amountToPay) => {
  //Find all zingcash document which {userId: userId, isExpired: false, status: ACTIVE, transactionType: CREDIT} and sort in ascending order by expiryDate
  data = Date from db
  
  let remainingAmountToPay = amountToPay
  const transactionToUpdate = [] // will contain all transaction id which will be completely used to pay amountToPay
  const breakTransaction = { _id: null, updateBody: {}}
  
  for (let i=0; i<data.length; ++i) {
    const {amount} = data[i]
    
    if(remainingAmountToPay === 0) {
      // Break the for loop if remainingAmountToPay becomes 0 before for loop ends
      break;
    }
    
    if(remainingAmountToPay >= amount) {
      remainingAmountToPay = remainingAmountToPay - amount
      transactionToUpdate.push(data[i]._id)
    }else {
      // Transaction to break
      breakTransaction._id = data[i]._id
      breakTransaction.updateBody.amount = amount - remainingAmountToPay
      
      remainingAmountToPay = 0
    } 
  }
  
  // Update all transactionToUpdate with updateBody = {amount: 0}
  
  if(breakTransaction._id) {
    // Update break transaction with update body = breakTransaction.body
  }
  
  
  const zingCashUsed = amountToPay - remainingAmountToPay
  
  // Add new DEBIT transaction for amountUsed = zingCashUsed
  
  return {remainingAmountToPay, zinCashUsed }
}


// CRON JOB

const zingCashExpireCron = () => {
  // Find all documents in zingcash with { status: ACTIVE, isExpired: false, expiryDate: { $lte: Date.now() } }
  const data = [] // zingcash data from db
  
  for(let i=0; i< data.length; ++i) {
    const {userId, amount} = data[i]
    
    // Add DEBIT transaction entry
  }
}