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/*
* Copyright (c) 2023 Vaughn Nugent
*
* Library: VNLib
* Package: VNLib.Data.Caching.ObjectCache
* File: BlobCacheExtensions.cs
*
* BlobCacheExtensions.cs is part of VNLib.Data.Caching.ObjectCache which is part of the larger
* VNLib collection of libraries and utilities.
*
* VNLib.Data.Caching.ObjectCache is free software: you can redistribute it and/or modify
* it under the terms of the GNU Affero General Public License as
* published by the Free Software Foundation, either version 3 of the
* License, or (at your option) any later version.
*
* VNLib.Data.Caching.ObjectCache is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU Affero General Public License for more details.
*
* You should have received a copy of the GNU Affero General Public License
* along with this program. If not, see https://www.gnu.org/licenses/.
*/
using System;
using System.Threading;
using System.Threading.Tasks;
namespace VNLib.Data.Caching.ObjectCache
{
/// <summary>
/// Provides blob cache extension methods
/// </summary>
public static class BlobCacheExtensions
{
internal static CacheEntry CreateEntry(this IBlobCache cache, string objectId, ReadOnlySpan<byte> initialData, DateTime time)
{
CacheEntry entry = CacheEntry.Create(initialData, cache.CacheHeap);
try
{
//try to add the entry, but if exists, let it throw
cache.Add(objectId, entry);
entry.SetTime(time);
return entry;
}
catch
{
entry.Dispose();
throw;
}
}
internal static CacheEntry AddOrUpdateEntry(this IBlobCache cache, string objectId, ReadOnlySpan<byte> data, DateTime time)
{
//See if blob exists
if (cache.TryGetValue(objectId, out CacheEntry entry))
{
//Update the entry since it exists
entry.UpdateData(data);
entry.SetTime(time);
}
else
{
//Create the new entry
entry = cache.CreateEntry(objectId, data, time);
}
return entry;
}
internal static CacheEntry TryChangeKey(this IBlobCache cache, string objectId, string alternateId, ReadOnlySpan<byte> data, DateTime time)
{
//Change the key of the blob item and update its data
if (cache.TryChangeKey(objectId, alternateId, out CacheEntry entry))
{
//If date is 0 length do not overwrite the old entry if found
if (data.IsEmpty)
{
return entry;
}
//Otherwise update the entry
entry.UpdateData(data);
entry.SetTime(time);
return entry;
}
else
{
//entry does not exist at the old id, so we can create a new one at the alternate id
return cache.CreateEntry(objectId, data, time);
}
}
/// <summary>
/// Asynchronously adds or updates an object in the store and optionally update's it's id
/// </summary>
/// <param name="table"></param>
/// <param name="objectId">The current (or old) id of the object</param>
/// <param name="alternateId">An optional id to update the blob to</param>
/// <param name="bodyData">A callback that returns the data for the blob</param>
/// <param name="state">The state parameter to pass to the data callback</param>
/// <param name="time">The time to set on the cache record</param>
/// <param name="cancellation">A token to cancel the async operation</param>
/// <returns>A value task that represents the async operation</returns>
public static async ValueTask AddOrUpdateObjectAsync<T>(
this IBlobCacheTable table,
string objectId,
string? alternateId,
GetBodyDataCallback<T> bodyData,
T state,
DateTime time,
CancellationToken cancellation = default)
{
//See if an id change is required
if (string.IsNullOrWhiteSpace(alternateId))
{
//safe to get the bucket for the primary id
IBlobCacheBucket bucket = table.GetBucket(objectId);
//Wait for the bucket
using CacheBucketHandle handle = await bucket.WaitAsync(cancellation);
//add/update for single entity
_ = handle.Cache.AddOrUpdateEntry(objectId, bodyData(state), time);
}
else
{
//Buckets for each id need to be obtained
IBlobCacheBucket primary = table.GetBucket(objectId);
IBlobCacheBucket alternate = table.GetBucket(alternateId);
//Same bucket
if (ReferenceEquals(primary, alternate))
{
//wait for lock on only one bucket otherwise dealock
using CacheBucketHandle handle = await primary.WaitAsync(cancellation);
//Update the entry for the single bucket
_ = handle.Cache.TryChangeKey(objectId, alternateId, bodyData(state), time);
}
else
{
//Buckets are different must be awaited individually
using CacheBucketHandle primaryHandle = await primary.WaitAsync(cancellation);
using CacheBucketHandle alternateHandle = await alternate.WaitAsync(cancellation);
//Get the entry from the primary hande
if (primaryHandle.Cache.Remove(objectId, out CacheEntry entry))
{
try
{
//Update the handle data and reuse the entry
entry.UpdateData(bodyData(state));
//Add the updated entry to the alternate table
alternateHandle.Cache.Add(alternateId, entry);
}
catch
{
//Cleanup handle if error adding
entry.Dispose();
throw;
}
}
else
{
//Old entry did not exist, we need to create a new entry for the alternate bucket
_ = alternateHandle.Cache.CreateEntry(alternateId, bodyData(state), time);
}
}
}
}
/// <summary>
/// Asynchronously deletes a previously stored item
/// </summary>
/// <param name="table"></param>
/// <param name="objectId">The id of the object to delete</param>
/// <param name="cancellation">A token to cancel the async lock await</param>
/// <returns>A task that completes when the item has been deleted</returns>
public static async ValueTask<bool> DeleteObjectAsync(this IBlobCacheTable table, string objectId, CancellationToken cancellation = default)
{
//Try to get the bucket that the id should belong to
IBlobCacheBucket bucket = table.GetBucket(objectId);
//Wait for lock on bucket async
using CacheBucketHandle handle = await bucket.WaitAsync(cancellation);
//Remove the object from the blob store
return handle.Cache.Remove(objectId);
}
}
}
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