// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT license.
 
using System;
using System.Buffers;
using System.Diagnostics;
using System.Threading;
using Microsoft.Shared.Diagnostics;
 
namespace Microsoft.Extensions.Caching.Hybrid.Internal;
 
// this is effectively a cut-down re-implementation of ArrayBufferWriter
// from https://github.com/dotnet/runtime/blob/6cd9bf1937c3b4d2f7304a6c534aacde58a202b6/src/libraries/Common/src/System/Buffers/ArrayBufferWriter.cs
// except it uses the array pool for allocations
internal sealed class RecyclableArrayBufferWriter<T> : IBufferWriter<T>, IDisposable
{
    // Usage note: *normally* you might want to use "using" for this, and that is fine
    // however, caution should be exercised in exception scenarios where we don't 100%
    // know that the caller has stopped touching the buffer; in particular, this means
    // scenarios involving a combination of external code and (for example) "async".
    // In those cases, it may be preferable to manually dispose in the success case,
    // and just drop the buffers in the failure case, i.e. instead of:
    //
    // using (writer)
    // { DoStuff(); }
    //
    // simply:
    //
    // DoStuff();
    // writer.Dispose();
    //
    // This does not represent a problem, and is consistent with many ArrayPool use-cases.
 
    // Copy of Array.MaxLength.
    // Used by projects targeting .NET Framework.
    [System.Diagnostics.CodeAnalysis.SuppressMessage("Major Code Smell", "S125:Sections of code should not be commented out", Justification = "Usage example, please retain")]
    private const int ArrayMaxLength = 0x7FFFFFC7;
 
    private const int DefaultInitialBufferSize = 256;
 
    private T[] _buffer;
    [System.Diagnostics.CodeAnalysis.SuppressMessage("Style", "IDE0032:Use auto property", Justification = "It is preferable to keep this usage explicit")]
    private int _index;
    private int _maxLength;
 
    public int CommittedBytes => _index;
    public int FreeCapacity => _buffer.Length - _index;
 
    private static RecyclableArrayBufferWriter<T>? _spare;
    public static RecyclableArrayBufferWriter<T> Create(int maxLength)
    {
        var obj = Interlocked.Exchange(ref _spare, null) ?? new();
        Debug.Assert(obj._index == 0, "index should be zero initially");
        obj._maxLength = maxLength;
        return obj;
    }
 
    private RecyclableArrayBufferWriter()
    {
        _buffer = [];
        _index = 0;
        _maxLength = int.MaxValue;
    }
 
    public void Dispose()
    {
        // attempt to reuse everything via "spare"; if that isn't possible,
        // recycle the buffers instead
        _index = 0;
        if (Interlocked.CompareExchange(ref _spare, this, null) != null)
        {
            var tmp = _buffer;
            _buffer = [];
            if (tmp.Length != 0)
            {
                ArrayPool<T>.Shared.Return(tmp);
            }
        }
    }
 
    [System.Diagnostics.CodeAnalysis.SuppressMessage("Major Code Smell", "S3928:Parameter names used into ArgumentException constructors should match an existing one ",
        Justification = "False positive; parameter exists")]
    public void Advance(int count)
    {
        _ = Throw.IfLessThan(count, 0);
 
        if (_index > _buffer.Length - count)
        {
            ThrowCount();
        }
 
        if (_index + count > _maxLength)
        {
            ThrowQuota();
        }
 
        _index += count;
 
        static void ThrowCount()
            => throw new ArgumentOutOfRangeException(nameof(count));
 
        static void ThrowQuota()
            => throw new InvalidOperationException("Max length exceeded");
    }
 
    public void ResetInPlace()
    {
        // resets the writer *without* resetting the buffer.
        // the existing memory should be considered "gone"
        // (to claim the buffer instead, use DetachCommitted)
        _index = 0;
    }
 
    public ReadOnlyMemory<T> GetCommittedMemory() => new(_buffer, 0, _index); // could also directly expose a ReadOnlySpan<byte> if useful
 
    public Memory<T> GetMemory(int sizeHint = 0)
    {
        CheckAndResizeBuffer(sizeHint);
        Debug.Assert(_buffer.Length > _index, "should have some space");
        return _buffer.AsMemory(_index);
    }
 
    public Span<T> GetSpan(int sizeHint = 0)
    {
        CheckAndResizeBuffer(sizeHint);
        Debug.Assert(_buffer.Length > _index, "should have some space");
        return _buffer.AsSpan(_index);
    }
 
    // create a standalone isolated copy of the buffer
    public T[] ToArray() => _buffer.AsSpan(0, _index).ToArray();
 
    /// <summary>
    /// Disconnect the current buffer so that we can store it without it being recycled.
    /// </summary>
    internal T[] DetachCommitted(out int length)
    {
        var tmp = _index == 0 ? [] : _buffer;
        length = _index;
 
        _buffer = [];
        _index = 0;
 
        return tmp;
    }
 
    internal T[] GetBuffer(out int length)
    {
        length = _index;
        return _index == 0 ? [] : _buffer;
    }
 
    private void CheckAndResizeBuffer(int sizeHint)
    {
        if (sizeHint <= 0)
        {
            sizeHint = 1;
        }
 
        if (sizeHint > FreeCapacity)
        {
            var currentLength = _buffer.Length;
 
            // Attempt to grow by the larger of the sizeHint and double the current size.
            var growBy = Math.Max(sizeHint, currentLength);
 
            if (currentLength == 0)
            {
                growBy = Math.Max(growBy, DefaultInitialBufferSize);
            }
 
            var newSize = currentLength + growBy;
 
            if ((uint)newSize > int.MaxValue)
            {
                // Attempt to grow to ArrayMaxLength.
                var needed = (uint)(currentLength - FreeCapacity + sizeHint);
                Debug.Assert(needed > currentLength, "should need to grow");
 
                if (needed > ArrayMaxLength)
                {
                    ThrowOutOfMemoryException();
                }
 
                newSize = ArrayMaxLength;
            }
 
            // resize the backing buffer
            var oldArray = _buffer;
            _buffer = ArrayPool<T>.Shared.Rent(newSize);
            oldArray.AsSpan(0, _index).CopyTo(_buffer);
            if (oldArray.Length != 0)
            {
                ArrayPool<T>.Shared.Return(oldArray);
            }
        }
 
        Debug.Assert(FreeCapacity > 0 && FreeCapacity >= sizeHint, "should be space");
 
        static void ThrowOutOfMemoryException() => throw new InvalidOperationException("Unable to grow buffer as requested");
    }
}