IBufferWriterStream{TWriter}.cs

// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT license.
// See the LICENSE file in the project root for more information.

using System;
using System.Buffers;
using System.IO;
using System.Runtime.CompilerServices;
using System.Threading;
using System.Threading.Tasks;

namespace CommunityToolkit.HighPerformance.Streams;

/// <summary>
/// A <see cref="Stream"/> implementation wrapping an <see cref="IBufferWriter{T}"/> instance.
/// </summary>
/// <typeparam name="TWriter">The type of buffer writer to use.</typeparam>
internal sealed partial class IBufferWriterStream<TWriter> : Stream
    where TWriter : struct, IBufferWriter<byte>
{
    /// <summary>
    /// The target <typeparamref name="TWriter"/> instance to use.
    /// </summary>
    private readonly TWriter bufferWriter;

    /// <summary>
    /// Indicates whether or not the current instance has been disposed
    /// </summary>
    private bool disposed;

    /// <summary>
    /// Initializes a new instance of the <see cref="IBufferWriterStream{TWriter}"/> class.
    /// </summary>
    /// <param name="bufferWriter">The target <see cref="IBufferWriter{T}"/> instance to use.</param>
    public IBufferWriterStream(TWriter bufferWriter)
    {
        this.bufferWriter = bufferWriter;
    }

    /// <inheritdoc/>
    public override bool CanRead => false;

    /// <inheritdoc/>
    public override bool CanSeek => false;

    /// <inheritdoc/>
    public override bool CanWrite
    {
        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        get => !this.disposed;
    }

    /// <inheritdoc/>
    public override long Length => throw MemoryStream.GetNotSupportedException();

    /// <inheritdoc/>
    public override long Position
    {
        get => throw MemoryStream.GetNotSupportedException();
        set => throw MemoryStream.GetNotSupportedException();
    }

    /// <inheritdoc/>
    public override Task CopyToAsync(Stream destination, int bufferSize, CancellationToken cancellationToken)
    {
        throw MemoryStream.GetNotSupportedException();
    }

    /// <inheritdoc/>
    public override void Flush()
    {
    }

    /// <inheritdoc/>
    public override Task FlushAsync(CancellationToken cancellationToken)
    {
        if (cancellationToken.IsCancellationRequested)
        {
            return Task.FromCanceled(cancellationToken);
        }

        return Task.CompletedTask;
    }

    /// <inheritdoc/>
    public override Task<int> ReadAsync(byte[]? buffer, int offset, int count, CancellationToken cancellationToken)
    {
        throw MemoryStream.GetNotSupportedException();
    }

    /// <inheritdoc/>
    public override Task WriteAsync(byte[]? buffer, int offset, int count, CancellationToken cancellationToken)
    {
        if (cancellationToken.IsCancellationRequested)
        {
            return Task.FromCanceled(cancellationToken);
        }

        try
        {
            Write(buffer, offset, count);

            return Task.CompletedTask;
        }
        catch (OperationCanceledException e)
        {
            return Task.FromCanceled(e.CancellationToken);
        }
        catch (Exception e)
        {
            return Task.FromException(e);
        }
    }

    /// <inheritdoc/>
    public override long Seek(long offset, SeekOrigin origin)
    {
        throw MemoryStream.GetNotSupportedException();
    }

    /// <inheritdoc/>
    public override void SetLength(long value)
    {
        throw MemoryStream.GetNotSupportedException();
    }

    /// <inheritdoc/>
    public override int Read(byte[]? buffer, int offset, int count)
    {
        throw MemoryStream.GetNotSupportedException();
    }

    /// <inheritdoc/>
    public override int ReadByte()
    {
        throw MemoryStream.GetNotSupportedException();
    }

    /// <inheritdoc/>
    public override void Write(byte[]? buffer, int offset, int count)
    {
        MemoryStream.ValidateDisposed(this.disposed);
        MemoryStream.ValidateBuffer(buffer, offset, count);

        Span<byte> source = buffer.AsSpan(offset, count);
        Span<byte> destination = this.bufferWriter.GetSpan(count);

        if (!source.TryCopyTo(destination))
        {
            MemoryStream.ThrowArgumentExceptionForEndOfStreamOnWrite();
        }

        this.bufferWriter.Advance(count);
    }

    /// <inheritdoc/>
    public override void WriteByte(byte value)
    {
        MemoryStream.ValidateDisposed(this.disposed);

        this.bufferWriter.GetSpan(1)[0] = value;

        this.bufferWriter.Advance(1);
    }

    /// <inheritdoc/>
    protected override void Dispose(bool disposing)
    {
        this.disposed = true;
    }
}