/// <summary>
/// Returns the time that the key was added to the cache, or returns
/// null if the key isn't in the cache.
/// </summary>
/// <param name="key">The key to return the date for.</param>
/// <returns>The date the key was created on.</returns>
public static IObservable <DateTimeOffset?> GetObjectCreatedAt <T>(this IBlobCache This, string key)
{
var objCache = This as IObjectBlobCache;
if (objCache != null)
{
return(This.GetCreatedAt(key));
}
return(This.GetCreatedAt(key));
}
/// <summary>
/// This is the non-generic analog of JsonSerializationMixin.GetAndFetchLatest[1]
/// We shouldn't make modifications to this that alter its behavior from the generic
/// version. By having this we can keep our two GetAndRefresh methods extremely
/// similar and thus trust that what works in one will work in the other.
///
/// 1. https://github.com/akavache/Akavache/blob/1b19bb56d/Akavache/Portable/JsonSerializationMixin.cs#L202-L236
/// </summary>
static IObservable <byte[]> GetAndFetchLatestBytes(
this IBlobCache blobCache,
string key,
Func <IObservable <byte[]> > fetchFunc,
Func <DateTimeOffset, bool> fetchPredicate = null,
DateTimeOffset?absoluteExpiration = null)
{
var fetch = Observable.Defer(() => blobCache.GetCreatedAt(key))
.Select(x => fetchPredicate == null || x == null || fetchPredicate(x.Value))
.Where(predicateIsTrue => predicateIsTrue)
.SelectMany(_ =>
{
return(fetchFunc()
.SelectMany(x => blobCache.Invalidate(key).Select(__ => x))
.SelectMany(x => blobCache.Insert(key, x, absoluteExpiration).Select(__ => x)));
});
var result = blobCache.Get(key).Select(x => Tuple.Create(x, true))
.Catch(Observable.Return(new Tuple <byte[], bool>(null, false)));
return(result
.SelectMany(x => x.Item2
? Observable.Return(x.Item1)
: Observable.Empty <byte[]>())
.Concat(fetch)
.Replay()
.RefCount());
}
/// <summary>
/// This method attempts to returned a cached value, while
/// simultaneously calling a Func to return the latest value. When the
/// latest data comes back, it replaces what was previously in the
/// cache.
///
/// This method is best suited for loading dynamic data from the
/// Internet, while still showing the user earlier data.
///
/// This method returns an IObservable that may return *two* results
/// (first the cached data, then the latest data). Therefore, it's
/// important for UI applications that in your Subscribe method, you
/// write the code to merge the second result when it comes in.
/// </summary>
/// <param name="key">The key to store the returned result under.</param>
/// <param name="fetchFunc"></param>
/// <param name="fetchPredicate">An optional Func to determine whether
/// the updated item should be fetched. If the cached version isn't found,
/// this parameter is ignored and the item is always fetched.</param>
/// <param name="absoluteExpiration">An optional expiration date.</param>
/// <returns>An Observable stream containing either one or two
/// results (possibly a cached version, then the latest version)</returns>
public static IObservable <T> GetAndFetchLatest <T>(this IBlobCache This,
string key,
Func <IObservable <T> > fetchFunc,
Func <DateTimeOffset, bool> fetchPredicate = null,
DateTimeOffset?absoluteExpiration = null)
{
bool foundItemInCache;
var fail = Observable.Defer(() => This.GetCreatedAt(key))
.Select(x => fetchPredicate != null && x != null ? fetchPredicate(x.Value) : true)
.Where(x => x != false)
.SelectMany(_ => fetchFunc())
.Finally(() => This.Invalidate(key))
.Do(x => This.InsertObject(key, x, absoluteExpiration));
var result = This.GetObjectAsync <T>(key).Select(x => new Tuple <T, bool>(x, true))
.Catch(Observable.Return(new Tuple <T, bool>(default(T), false)));
return(result.SelectMany(x =>
{
foundItemInCache = x.Item2;
return x.Item2 ?
Observable.Return(x.Item1) :
Observable.Empty <T>();
}).Concat(fail).Multicast(new ReplaySubject <T>()).RefCount());
}
public bool ContainsKey(string key)
{
var result = blobCache.GetCreatedAt(key).Wait();
// FIX: Temporarily logging this, as I suspect it of always returning true
Log.Verbose(TAG, $"ContainsKey: {key} = {result.HasValue}");
return(result.HasValue);
}
/// <summary>
/// Returns the time that the key was added to the cache, or returns
/// null if the key isn't in the cache.
/// </summary>
/// <typeparam name="T">The type of item to get.</typeparam>
/// <param name="blobCache">The cache to get the item.</param>
/// <param name="key">The key to return the date for.</param>
/// <returns>The date the key was created on.</returns>
public static IObservable <DateTimeOffset?> GetObjectCreatedAt <T>(this IBlobCache blobCache, string key)
{
if (blobCache is IObjectBlobCache objCache)
{
return(objCache.GetObjectCreatedAt <T>(key));
}
return(blobCache.GetCreatedAt(GetTypePrefixedKey(key, typeof(T))));
}
/// <summary>
/// Gets a dictionary filled with the specified keys with their corresponding created <see cref="DateTimeOffset"/>
/// if it's available.
/// </summary>
/// <param name="blobCache">The blob cache to extract the values from.</param>
/// <param name="keys">The keys to get the values for.</param>
/// <returns>A observable with the specified values.</returns>
public static IObservable <IDictionary <string, DateTimeOffset?> > GetCreatedAt(this IBlobCache blobCache, IEnumerable <string> keys)
{
if (blobCache is IBulkBlobCache bulkCache)
{
return(bulkCache.GetCreatedAt(keys));
}
return(keys.ToObservable()
.SelectMany(x => blobCache.GetCreatedAt(x).Select(y => new { Key = x, Value = y }))
.ToDictionary(k => k.Key, v => v.Value));
}
/// <summary>
/// Returns the time that the key was added to the cache, or returns
/// null if the key isn't in the cache.
/// </summary>
/// <param name="key">The key to return the date for.</param>
/// <returns>The date the key was created on.</returns>
public static IObservable <DateTimeOffset?> GetObjectCreatedAt <T>(this IBlobCache This, string key)
{
var objCache = This as IObjectBlobCache;
if (objCache != null)
{
return(objCache.GetObjectCreatedAt <T>(key));
}
return(This.GetCreatedAt(GetTypePrefixedKey(key, typeof(T))));
}
/// <summary>
/// Returns the time that the key was added to the cache, or returns
/// null if the key isn't in the cache.
/// </summary>
/// <typeparam name="T">The type of item to get.</typeparam>
/// <param name="blobCache">The cache to get the item.</param>
/// <param name="key">The key to return the date for.</param>
/// <returns>The date the key was created on.</returns>
public static IObservable <DateTimeOffset?> GetObjectCreatedAt <T>(this IBlobCache blobCache, string key)
{
if (blobCache is null)
{
throw new ArgumentNullException(nameof(blobCache));
}
if (blobCache is IObjectBlobCache objCache)
{
return(objCache.GetObjectCreatedAt <T>(key));
}
return(blobCache.GetCreatedAt(GetTypePrefixedKey(key, typeof(T))));
}
static IObservable <Unit> VacuumIfNecessary(IBlobCache blobCache, bool force = false)
{
const string key = "__Vacuumed";
var vauumInterval = TimeSpan.FromDays(30);
return(Observable.Defer(() => blobCache.GetCreatedAt(key))
.Where(lastVacuum => force || !lastVacuum.HasValue || blobCache.Scheduler.Now - lastVacuum.Value > vauumInterval)
.SelectMany(Observable.Defer(blobCache.Vacuum))
.SelectMany(Observable.Defer(() => blobCache.Insert(key, new byte[] { 1 })))
.Catch <Unit, Exception>(ex =>
{
log.Error("Could not vacuum image cache", ex);
return Observable.Return(Unit.Default);
})
.AsCompletion());
}
public IObservable <DateTimeOffset?> GetCreatedAt(string key)
{
return(_inner.GetCreatedAt(key));
}
public static bool NeedsMigration(IBlobCache blobCache)
{
return(blobCache.GetCreatedAt(MigratedKey).Wait() == null);
}
public static bool NeedsMigration(IBlobCache blobCache)
{
return blobCache.GetCreatedAt(MigratedKey).Wait() == null;
}