/*
* Copyright (c) 2023 Vaughn Nugent
* 
* Library: VNLib
* Package: VNLib.Data.Caching.ObjectCache
* File: BlobCacheBucket.cs 
*
* BlobCacheBucket.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.Threading;
using System.Threading.Tasks;

using VNLib.Utils.Memory;

namespace VNLib.Data.Caching.ObjectCache
{
    public sealed class BlobCacheBucket : IBlobCacheBucket
    {
        private readonly IBlobCache _cacheTable;
        private readonly SemaphoreSlim _lock;

        /// <summary>
        /// Initialzies a new <see cref="BlobCacheBucket"/> and its underlying
        /// <see cref="IBlobCache"/>
        /// </summary>
        /// <param name="bucketCapacity">
        /// The maxium number of entries allowed in the LRU cache
        /// before LRU overflow happens.
        /// </param>
        /// <param name="heap">The heap to allocate object cache buffers</param>
        public BlobCacheBucket(int bucketCapacity, IUnmangedHeap heap)
        {
            _lock = new(1, 1);
            _cacheTable = new BlobCache(bucketCapacity, heap);
        }

        ///<inheritdoc/>
        public void Dispose()
        {
            _cacheTable.Dispose();
            _lock.Dispose();
        }

        ///<inheritdoc/>
        public async ValueTask<IBlobCache> ManualWaitAsync(CancellationToken cancellation)
        {
            //try to enter the lock synchronously
            if (_lock.Wait(0, CancellationToken.None))
            {
                return _cacheTable;
            }
            else
            {
                await _lock.WaitAsync(cancellation).ConfigureAwait(false);
                return _cacheTable;
            }
        }

        ///<inheritdoc/>
        public void Release()
        {
            _lock.Release();
        }

        ///<inheritdoc/>
        public async ValueTask<CacheBucketHandle> WaitAsync(CancellationToken cancellation)
        {
            //try to enter the lock synchronously
            if (_lock.Wait(0, CancellationToken.None))
            {
                return new(this, _cacheTable);
            }
            else
            {
                await _lock.WaitAsync(cancellation).ConfigureAwait(false);
                return new(this, _cacheTable);
            }
        }
    }
}