private void checkPurchaseHistory() {
        Purchase.PurchasesResult purchasesResult=mBillingClient.queryPurchases(BillingClient.SkuType.SUBS); //we want to check subscription
        if (purchasesResult!=null && purchasesResult.getPurchasesList()!=null && purchasesResult.getPurchasesList().size()>0){
            //so minimum one purchase was actually made
            for (Purchase purchase:purchasesResult.getPurchasesList()) {
                if (monthlySku.equals(purchase.getSku())){
                    //we know monthly sub last 30 days and api gives us purchase time.
                    long purchaseTime=purchase.getPurchaseTime();
                    Calendar purchaseDate=Calendar.getInstance();
                    purchaseDate.setTimeInMillis(purchaseTime);
                    Calendar currentDate=Calendar.getInstance();
                    long days=calendarDaysBetween(purchaseDate,currentDate);
                    if (days>30){
                        //monthly expired
                    }
                    Toast.makeText(this,"Remaining days: "
                            +days,Toast.LENGTH_LONG).show();

                }
            }
        }
    }
    public static long calendarDaysBetween(Calendar startCal, Calendar endCal) {

        // Create copies so we don't update the original calendars.

        Calendar start = Calendar.getInstance();
        start.setTimeZone(startCal.getTimeZone());
        start.setTimeInMillis(startCal.getTimeInMillis());

        Calendar end = Calendar.getInstance();
        end.setTimeZone(endCal.getTimeZone());
        end.setTimeInMillis(endCal.getTimeInMillis());

        // Set the copies to be at midnight, but keep the day information.

        start.set(Calendar.HOUR_OF_DAY, 0);
        start.set(Calendar.MINUTE, 0);
        start.set(Calendar.SECOND, 0);
        start.set(Calendar.MILLISECOND, 0);

        end.set(Calendar.HOUR_OF_DAY, 0);
        end.set(Calendar.MINUTE, 0);
        end.set(Calendar.SECOND, 0);
        end.set(Calendar.MILLISECOND, 0);

        // At this point, each calendar is set to midnight on
        // their respective days. Now use TimeUnit.MILLISECONDS to
        // compute the number of full days between the two of them.

        return TimeUnit.MILLISECONDS.toDays(
                Math.abs(end.getTimeInMillis() - start.getTimeInMillis()));
    }