/// <summary>
/// Attempts to get the cache entry which was last stored for the given fingerprint
/// </summary>
public static async Task <Possible <CacheEntry?> > TryGetLatestCacheEntryAsync(
this ITwoPhaseFingerprintStore store,
LoggingContext loggingContext,
ContentFingerprint fingerprint,
DateTime?time = null)
{
// This method starts at a leaf time node and traverses up until a parent node
// is found which has a corresponding cache entry. Then the children of that parent
// node are iterated recursively (latest in time first) to find the node that closest in time
// to the specified time parameter. This yields the cache entry added most recently.
var node = new TimeTreeNode(time);
while (node != null)
{
var getResult = await store.TryGetTemporalCacheEntryAsync(loggingContext, node, fingerprint);
if (!getResult.Succeeded)
{
return(getResult);
}
else if (getResult.Result != null)
{
return(await TryGetLatestChildCacheEntryAsync(loggingContext, node, store, fingerprint, getResult));
}
node = node.Parent;
}
return((CacheEntry?)null);
}
/// <summary>
/// Attempts to get the cache entry for the child which comes latest in time
/// </summary>
private static async Task <Possible <CacheEntry?> > TryGetLatestChildCacheEntryAsync(
LoggingContext loggingContext,
TimeTreeNode node,
ITwoPhaseFingerprintStore store,
ContentFingerprint fingerprint,
Possible <CacheEntry?> fallbackResult)
{
var childNodes = node.Children;
var children = childNodes.Select(childNode => store.TryGetTemporalCacheEntryAsync(loggingContext, childNode, fingerprint)).ToList();
var childResults = await Task.WhenAll(children);
// In reverse order (i.e. later in time), check children to see which
// one has results
for (int i = childResults.Length - 1; i >= 0; i--)
{
var childResult = childResults[i];
var childNode = childNodes[i];
if (!childResult.Succeeded)
{
continue;
}
if (childResult.Result != null)
{
return(await TryGetLatestChildCacheEntryAsync(
loggingContext,
childNode,
store,
fingerprint,
childResult));
}
}
return(fallbackResult);
}