public static long GetRemainingCredits(this DataCache dataCache, string account, long cost, long initialCredits,
TimeSpan timeout, ICostCalculator costCalculator)
{
if (string.IsNullOrWhiteSpace(account))
{
throw new ArgumentNullException("account");
}
if (cost <= 0)
{
throw new ArgumentOutOfRangeException("cost", "Cost cannot be negative");
}
if (initialCredits <= 0)
{
throw new ArgumentOutOfRangeException("initialCredits", "Initial credit cannot be negative");
}
if (timeout.TotalMilliseconds <= 0)
{
throw new ArgumentOutOfRangeException("timeout", "Timeout must be a time interval");
}
DataCacheItem cacheItem = dataCache.GetCacheItem(account);
long remainingCredits;
if (cacheItem == null)
{
remainingCredits = costCalculator.CalculateRemainingCredits(initialCredits, cost);
if (remainingCredits <= 0)
{
return remainingCredits;
}
dataCache.Add(account, remainingCredits, timeout);
return remainingCredits;
}
if (!(cacheItem.Value is long))
{
throw new InvalidOperationException(string.Format("The cached value with key {0} is not a valid long",
account));
}
var cachedValue = (long) cacheItem.Value;
if (cachedValue <= 0)
{
return -1;
}
remainingCredits = costCalculator.CalculateRemainingCredits(cachedValue, cost);
var newTimeout = cacheItem.Timeout;
dataCache.Put(account, remainingCredits, cacheItem.Version, newTimeout);
return remainingCredits;
}