// 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.IO;
using System.Linq;
using System.Threading.Tasks;
using Microsoft.AspNetCore.Testing;
using Moq;
using Xunit;

namespace Microsoft.AspNetCore.WebUtilities
{
    public class FileBufferingReadStreamTests
    {
        private Stream MakeStream(int size)
        {
            // TODO: Fill with random data? Make readonly?
            return new MemoryStream(new byte[size]);
        }

        [Fact]
        public void FileBufferingReadStream_Properties_ExpectedValues()
        {
            var inner = MakeStream(1024 * 2);
            using (var stream = new FileBufferingReadStream(inner, 1024, null, Directory.GetCurrentDirectory()))
            {
                Assert.True(stream.CanRead);
                Assert.True(stream.CanSeek);
                Assert.False(stream.CanWrite);
                Assert.Equal(0, stream.Length); // Nothing buffered yet
                Assert.Equal(0, stream.Position);
                Assert.True(stream.InMemory);
                Assert.Null(stream.TempFileName);
            }
        }

        [Fact]
        public void FileBufferingReadStream_Sync0ByteReadUnderThreshold_DoesntCreateFile()
        {
            var inner = MakeStream(1024);
            using (var stream = new FileBufferingReadStream(inner, 1024 * 2, null, Directory.GetCurrentDirectory()))
            {
                var bytes = new byte[1000];
                var read0 = stream.Read(bytes, 0, 0);
                Assert.Equal(0, read0);
                Assert.Equal(read0, stream.Length);
                Assert.Equal(read0, stream.Position);
                Assert.True(stream.InMemory);
                Assert.Null(stream.TempFileName);

                var read1 = stream.Read(bytes, 0, bytes.Length);
                Assert.Equal(bytes.Length, read1);
                Assert.Equal(read0 + read1, stream.Length);
                Assert.Equal(read0 + read1, stream.Position);
                Assert.True(stream.InMemory);
                Assert.Null(stream.TempFileName);

                var read2 = stream.Read(bytes, 0, bytes.Length);
                Assert.Equal(inner.Length - read0 - read1, read2);
                Assert.Equal(read0 + read1 + read2, stream.Length);
                Assert.Equal(read0 + read1 + read2, stream.Position);
                Assert.True(stream.InMemory);
                Assert.Null(stream.TempFileName);

                var read3 = stream.Read(bytes, 0, bytes.Length);
                Assert.Equal(0, read3);
            }
        }

        [Fact]
        public void FileBufferingReadStream_SyncReadUnderThreshold_DoesntCreateFile()
        {
            var inner = MakeStream(1024 * 2);
            using (var stream = new FileBufferingReadStream(inner, 1024 * 3, null, Directory.GetCurrentDirectory()))
            {
                var bytes = new byte[1000];
                var read0 = stream.Read(bytes, 0, bytes.Length);
                Assert.Equal(bytes.Length, read0);
                Assert.Equal(read0, stream.Length);
                Assert.Equal(read0, stream.Position);
                Assert.True(stream.InMemory);
                Assert.Null(stream.TempFileName);

                var read1 = stream.Read(bytes, 0, bytes.Length);
                Assert.Equal(bytes.Length, read1);
                Assert.Equal(read0 + read1, stream.Length);
                Assert.Equal(read0 + read1, stream.Position);
                Assert.True(stream.InMemory);
                Assert.Null(stream.TempFileName);

                var read2 = stream.Read(bytes, 0, bytes.Length);
                Assert.Equal(inner.Length - read0 - read1, read2);
                Assert.Equal(read0 + read1 + read2, stream.Length);
                Assert.Equal(read0 + read1 + read2, stream.Position);
                Assert.True(stream.InMemory);
                Assert.Null(stream.TempFileName);

                var read3 = stream.Read(bytes, 0, bytes.Length);
                Assert.Equal(0, read3);
            }
        }

        [Fact]
        public void FileBufferingReadStream_SyncReadOverThreshold_CreatesFile()
        {
            var inner = MakeStream(1024 * 2);
            string tempFileName;
            using (var stream = new FileBufferingReadStream(inner, 1024, null, GetCurrentDirectory()))
            {
                var bytes = new byte[1000];
                var read0 = stream.Read(bytes, 0, bytes.Length);
                Assert.Equal(bytes.Length, read0);
                Assert.Equal(read0, stream.Length);
                Assert.Equal(read0, stream.Position);
                Assert.True(stream.InMemory);
                Assert.Null(stream.TempFileName);

                var read1 = stream.Read(bytes, 0, bytes.Length);
                Assert.Equal(bytes.Length, read1);
                Assert.Equal(read0 + read1, stream.Length);
                Assert.Equal(read0 + read1, stream.Position);
                Assert.False(stream.InMemory);
                Assert.NotNull(stream.TempFileName);
                tempFileName = stream.TempFileName!;
                Assert.True(File.Exists(tempFileName));

                var read2 = stream.Read(bytes, 0, bytes.Length);
                Assert.Equal(inner.Length - read0 - read1, read2);
                Assert.Equal(read0 + read1 + read2, stream.Length);
                Assert.Equal(read0 + read1 + read2, stream.Position);
                Assert.False(stream.InMemory);
                Assert.NotNull(stream.TempFileName);
                Assert.True(File.Exists(tempFileName));

                var read3 = stream.Read(bytes, 0, bytes.Length);
                Assert.Equal(0, read3);
            }

            Assert.False(File.Exists(tempFileName));
        }

        [Fact]
        public void FileBufferingReadStream_SyncReadWithInMemoryLimit_EnforcesLimit()
        {
            var inner = MakeStream(1024 * 2);
            using (var stream = new FileBufferingReadStream(inner, 1024, 900, Directory.GetCurrentDirectory()))
            {
                var bytes = new byte[500];
                var read0 = stream.Read(bytes, 0, bytes.Length);
                Assert.Equal(bytes.Length, read0);
                Assert.Equal(read0, stream.Length);
                Assert.Equal(read0, stream.Position);
                Assert.True(stream.InMemory);
                Assert.Null(stream.TempFileName);

                var exception = Assert.Throws<IOException>(() => stream.Read(bytes, 0, bytes.Length));
                Assert.Equal("Buffer limit exceeded.", exception.Message);
                Assert.True(stream.InMemory);
                Assert.Null(stream.TempFileName);
                Assert.False(File.Exists(stream.TempFileName));
            }
        }

        [Fact]
        public void FileBufferingReadStream_SyncReadWithOnDiskLimit_EnforcesLimit()
        {
            var inner = MakeStream(1024 * 2);
            string tempFileName;
            using (var stream = new FileBufferingReadStream(inner, 512, 1024, GetCurrentDirectory()))
            {
                var bytes = new byte[500];
                var read0 = stream.Read(bytes, 0, bytes.Length);
                Assert.Equal(bytes.Length, read0);
                Assert.Equal(read0, stream.Length);
                Assert.Equal(read0, stream.Position);
                Assert.True(stream.InMemory);
                Assert.Null(stream.TempFileName);

                var read1 = stream.Read(bytes, 0, bytes.Length);
                Assert.Equal(bytes.Length, read1);
                Assert.Equal(read0 + read1, stream.Length);
                Assert.Equal(read0 + read1, stream.Position);
                Assert.False(stream.InMemory);
                Assert.NotNull(stream.TempFileName);
                tempFileName = stream.TempFileName!;
                Assert.True(File.Exists(tempFileName));

                var exception = Assert.Throws<IOException>(() => stream.Read(bytes, 0, bytes.Length));
                Assert.Equal("Buffer limit exceeded.", exception.Message);
                Assert.False(stream.InMemory);
                Assert.NotNull(stream.TempFileName);
            }

            Assert.False(File.Exists(tempFileName));
        }

        ///////////////////

        [Fact]
        public async Task FileBufferingReadStream_Async0ByteReadUnderThreshold_DoesntCreateFile()
        {
            var inner = MakeStream(1024);
            using (var stream = new FileBufferingReadStream(inner, 1024 * 2, null, Directory.GetCurrentDirectory()))
            {
                var bytes = new byte[1000];
                var read0 = await stream.ReadAsync(bytes, 0, 0);
                Assert.Equal(0, read0);
                Assert.Equal(read0, stream.Length);
                Assert.Equal(read0, stream.Position);
                Assert.True(stream.InMemory);
                Assert.Null(stream.TempFileName);

                var read1 = await stream.ReadAsync(bytes, 0, bytes.Length);
                Assert.Equal(bytes.Length, read1);
                Assert.Equal(read0 + read1, stream.Length);
                Assert.Equal(read0 + read1, stream.Position);
                Assert.True(stream.InMemory);
                Assert.Null(stream.TempFileName);

                var read2 = await stream.ReadAsync(bytes, 0, bytes.Length);
                Assert.Equal(inner.Length - read0 - read1, read2);
                Assert.Equal(read0 + read1 + read2, stream.Length);
                Assert.Equal(read0 + read1 + read2, stream.Position);
                Assert.True(stream.InMemory);
                Assert.Null(stream.TempFileName);

                var read3 = await stream.ReadAsync(bytes, 0, bytes.Length);
                Assert.Equal(0, read3);
            }
        }

        [Fact]
        public async Task FileBufferingReadStream_AsyncReadUnderThreshold_DoesntCreateFile()
        {
            var inner = MakeStream(1024 * 2);
            using (var stream = new FileBufferingReadStream(inner, 1024 * 3, null, Directory.GetCurrentDirectory()))
            {
                var bytes = new byte[1000];
                var read0 = await stream.ReadAsync(bytes, 0, bytes.Length);
                Assert.Equal(bytes.Length, read0);
                Assert.Equal(read0, stream.Length);
                Assert.Equal(read0, stream.Position);
                Assert.True(stream.InMemory);
                Assert.Null(stream.TempFileName);

                var read1 = await stream.ReadAsync(bytes, 0, bytes.Length);
                Assert.Equal(bytes.Length, read1);
                Assert.Equal(read0 + read1, stream.Length);
                Assert.Equal(read0 + read1, stream.Position);
                Assert.True(stream.InMemory);
                Assert.Null(stream.TempFileName);

                var read2 = await stream.ReadAsync(bytes, 0, bytes.Length);
                Assert.Equal(inner.Length - read0 - read1, read2);
                Assert.Equal(read0 + read1 + read2, stream.Length);
                Assert.Equal(read0 + read1 + read2, stream.Position);
                Assert.True(stream.InMemory);
                Assert.Null(stream.TempFileName);

                var read3 = await stream.ReadAsync(bytes, 0, bytes.Length);
                Assert.Equal(0, read3);
            }
        }

        [Fact]
        public async Task FileBufferingReadStream_AsyncReadOverThreshold_CreatesFile()
        {
            var inner = MakeStream(1024 * 2);
            string tempFileName;
            using (var stream = new FileBufferingReadStream(inner, 1024, null, GetCurrentDirectory()))
            {
                var bytes = new byte[1000];
                var read0 = await stream.ReadAsync(bytes, 0, bytes.Length);
                Assert.Equal(bytes.Length, read0);
                Assert.Equal(read0, stream.Length);
                Assert.Equal(read0, stream.Position);
                Assert.True(stream.InMemory);
                Assert.Null(stream.TempFileName);

                var read1 = await stream.ReadAsync(bytes, 0, bytes.Length);
                Assert.Equal(bytes.Length, read1);
                Assert.Equal(read0 + read1, stream.Length);
                Assert.Equal(read0 + read1, stream.Position);
                Assert.False(stream.InMemory);
                Assert.NotNull(stream.TempFileName);
                tempFileName = stream.TempFileName!;
                Assert.True(File.Exists(tempFileName));

                var read2 = await stream.ReadAsync(bytes, 0, bytes.Length);
                Assert.Equal(inner.Length - read0 - read1, read2);
                Assert.Equal(read0 + read1 + read2, stream.Length);
                Assert.Equal(read0 + read1 + read2, stream.Position);
                Assert.False(stream.InMemory);
                Assert.NotNull(stream.TempFileName);
                Assert.True(File.Exists(tempFileName));

                var read3 = await stream.ReadAsync(bytes, 0, bytes.Length);
                Assert.Equal(0, read3);
            }

            Assert.False(File.Exists(tempFileName));
        }

        [Fact]
        public async Task FileBufferingReadStream_Async0ByteReadAfterBuffering_ReadsFromFile()
        {
            var inner = MakeStream(1024 * 2);
            string tempFileName;
            using (var stream = new FileBufferingReadStream(inner, 1024, null, GetCurrentDirectory()))
            {
                await stream.DrainAsync(default);
                stream.Position = 0;
                Assert.Equal(inner.Length, stream.Length);
                Assert.Equal(0, stream.Position);
                Assert.False(stream.InMemory);
                Assert.NotNull(stream.TempFileName);
                tempFileName = stream.TempFileName!;
                Assert.True(File.Exists(tempFileName));

                var bytes = new byte[1000];
                var read0 = await stream.ReadAsync(bytes, 0, 0);
                Assert.Equal(0, read0);
                Assert.Equal(read0, stream.Position);

                var read1 = await stream.ReadAsync(bytes, 0, bytes.Length);
                Assert.Equal(bytes.Length, read1);
                Assert.Equal(read0 + read1, stream.Position);

                var read2 = await stream.ReadAsync(bytes, 0, bytes.Length);
                Assert.Equal(bytes.Length, read2);
                Assert.Equal(read0 + read1 + read2, stream.Position);

                var read3 = await stream.ReadAsync(bytes, 0, bytes.Length);
                Assert.Equal(inner.Length - read0 - read1 - read2, read3);
                Assert.Equal(read0 + read1 + read2 + read3, stream.Length);
                Assert.Equal(read0 + read1 + read2 + read3, stream.Position);

                var read4 = await stream.ReadAsync(bytes, 0, bytes.Length);
                Assert.Equal(0, read4);
            }

            Assert.False(File.Exists(tempFileName));
        }

        [Fact]
        public async Task FileBufferingReadStream_AsyncReadWithInMemoryLimit_EnforcesLimit()
        {
            var inner = MakeStream(1024 * 2);
            using (var stream = new FileBufferingReadStream(inner, 1024, 900, Directory.GetCurrentDirectory()))
            {
                var bytes = new byte[500];
                var read0 = await stream.ReadAsync(bytes, 0, bytes.Length);
                Assert.Equal(bytes.Length, read0);
                Assert.Equal(read0, stream.Length);
                Assert.Equal(read0, stream.Position);
                Assert.True(stream.InMemory);
                Assert.Null(stream.TempFileName);

                var exception = await Assert.ThrowsAsync<IOException>(() => stream.ReadAsync(bytes, 0, bytes.Length));
                Assert.Equal("Buffer limit exceeded.", exception.Message);
                Assert.True(stream.InMemory);
                Assert.Null(stream.TempFileName);
                Assert.False(File.Exists(stream.TempFileName));
            }
        }

        [Fact]
        public async Task FileBufferingReadStream_AsyncReadWithOnDiskLimit_EnforcesLimit()
        {
            var inner = MakeStream(1024 * 2);
            string tempFileName;
            using (var stream = new FileBufferingReadStream(inner, 512, 1024, GetCurrentDirectory()))
            {
                var bytes = new byte[500];
                var read0 = await stream.ReadAsync(bytes, 0, bytes.Length);
                Assert.Equal(bytes.Length, read0);
                Assert.Equal(read0, stream.Length);
                Assert.Equal(read0, stream.Position);
                Assert.True(stream.InMemory);
                Assert.Null(stream.TempFileName);

                var read1 = await stream.ReadAsync(bytes, 0, bytes.Length);
                Assert.Equal(bytes.Length, read1);
                Assert.Equal(read0 + read1, stream.Length);
                Assert.Equal(read0 + read1, stream.Position);
                Assert.False(stream.InMemory);
                Assert.NotNull(stream.TempFileName);
                tempFileName = stream.TempFileName!;
                Assert.True(File.Exists(tempFileName));

                var exception = await Assert.ThrowsAsync<IOException>(() => stream.ReadAsync(bytes, 0, bytes.Length));
                Assert.Equal("Buffer limit exceeded.", exception.Message);
                Assert.False(stream.InMemory);
                Assert.NotNull(stream.TempFileName);
            }

            Assert.False(File.Exists(tempFileName));
        }

        [Fact]
        public void FileBufferingReadStream_UsingMemoryStream_RentsAndReturnsRentedBuffer_WhenCopyingFromMemoryStreamDuringRead()
        {
            var inner = MakeStream(1024 * 1024 + 25);
            string tempFileName;
            var arrayPool = new Mock<ArrayPool<byte>>();
            arrayPool.Setup(p => p.Rent(It.IsAny<int>()))
                .Returns((int m) => ArrayPool<byte>.Shared.Rent(m));
            arrayPool.Setup(p => p.Return(It.IsAny<byte[]>(), It.IsAny<bool>()))
                .Callback((byte[] bytes, bool clear) => ArrayPool<byte>.Shared.Return(bytes, clear));

            using (var stream = new FileBufferingReadStream(inner, 1024 * 1024 + 1, 2 * 1024 * 1024, GetCurrentDirectory(), arrayPool.Object))
            {
                arrayPool.Verify(v => v.Rent(It.IsAny<int>()), Times.Never());

                stream.Read(new byte[1024 * 1024]);
                Assert.False(File.Exists(stream.TempFileName), "tempFile should not be created as yet");

                stream.Read(new byte[4]);
                Assert.True(File.Exists(stream.TempFileName), "tempFile should be created");
                tempFileName = stream.TempFileName!;

                arrayPool.Verify(v => v.Rent(It.IsAny<int>()), Times.Once());
                arrayPool.Verify(v => v.Return(It.IsAny<byte[]>(), It.IsAny<bool>()), Times.Once());
            }

            Assert.False(File.Exists(tempFileName));
        }

        [Fact]
        public async Task FileBufferingReadStream_UsingMemoryStream_RentsAndReturnsRentedBuffer_WhenCopyingFromMemoryStreamDuringReadAsync()
        {
            var inner = MakeStream(1024 * 1024 + 25);
            string tempFileName;
            var arrayPool = new Mock<ArrayPool<byte>>();
            arrayPool.Setup(p => p.Rent(It.IsAny<int>()))
                .Returns((int m) => ArrayPool<byte>.Shared.Rent(m));
            arrayPool.Setup(p => p.Return(It.IsAny<byte[]>(), It.IsAny<bool>()))
                .Callback((byte[] bytes, bool clear) => ArrayPool<byte>.Shared.Return(bytes, clear));

            using (var stream = new FileBufferingReadStream(inner, 1024 * 1024 + 1, 2 * 1024 * 1024, GetCurrentDirectory(), arrayPool.Object))
            {
                arrayPool.Verify(v => v.Rent(It.IsAny<int>()), Times.Never());

                await stream.ReadAsync(new byte[1024 * 1024]);
                Assert.False(File.Exists(stream.TempFileName), "tempFile should not be created as yet");

                await stream.ReadAsync(new byte[4]);
                Assert.True(File.Exists(stream.TempFileName), "tempFile should be created");
                tempFileName = stream.TempFileName!;

                arrayPool.Verify(v => v.Rent(It.IsAny<int>()), Times.Once());
                arrayPool.Verify(v => v.Return(It.IsAny<byte[]>(), It.IsAny<bool>()), Times.Once());
            }

            Assert.False(File.Exists(tempFileName));
        }

        [Fact]
        public async Task CopyToAsyncWorks()
        {
            // 4K is the lower bound on buffer sizes
            var bufferSize = 4096;
            var mostExpectedWrites = 8;
            var data = Enumerable.Range(0, bufferSize * mostExpectedWrites).Select(b => (byte)b).ToArray();
            var inner = new MemoryStream(data);

            using var stream = new FileBufferingReadStream(inner, 1024 * 1024, bufferLimit: null, GetCurrentDirectory());

            var withoutBufferMs = new NumberOfWritesMemoryStream();
            await stream.CopyToAsync(withoutBufferMs);

            var withBufferMs = new NumberOfWritesMemoryStream();
            stream.Position = 0;
            await stream.CopyToAsync(withBufferMs);

            Assert.Equal(data, withoutBufferMs.ToArray());
            Assert.Equal(mostExpectedWrites, withoutBufferMs.NumberOfWrites);
            Assert.Equal(data, withBufferMs.ToArray());
            Assert.InRange(withBufferMs.NumberOfWrites, 1, mostExpectedWrites);
        }

        [Fact]
        public async Task CopyToAsyncWorksWithFileThreshold()
        {
            // 4K is the lower bound on buffer sizes
            var bufferSize = 4096;
            var mostExpectedWrites = 8;
            var data = Enumerable.Range(0, bufferSize * mostExpectedWrites).Select(b => (byte)b).Reverse().ToArray();
            var inner = new MemoryStream(data);

            using var stream = new FileBufferingReadStream(inner, 100, bufferLimit: null, GetCurrentDirectory());

            var withoutBufferMs = new NumberOfWritesMemoryStream();
            await stream.CopyToAsync(withoutBufferMs);

            var withBufferMs = new NumberOfWritesMemoryStream();
            stream.Position = 0;
            await stream.CopyToAsync(withBufferMs);

            Assert.Equal(data, withoutBufferMs.ToArray());
            Assert.Equal(mostExpectedWrites, withoutBufferMs.NumberOfWrites);
            Assert.Equal(data, withBufferMs.ToArray());
            Assert.InRange(withBufferMs.NumberOfWrites, 1, mostExpectedWrites);
        }

        [Fact]
        public async Task ReadAsyncThenCopyToAsyncWorks()
        {
            var data = Enumerable.Range(0, 1024).Select(b => (byte)b).ToArray();
            var inner = new MemoryStream(data);

            using var stream = new FileBufferingReadStream(inner, 1024 * 1024, bufferLimit: null, GetCurrentDirectory());

            var withoutBufferMs = new MemoryStream();
            var buffer = new byte[100];
            await stream.ReadAsync(buffer);
            await stream.CopyToAsync(withoutBufferMs);

            Assert.Equal(data.AsMemory(0, 100).ToArray(), buffer);
            Assert.Equal(data.AsMemory(100).ToArray(), withoutBufferMs.ToArray());
        }

        [Fact]
        public async Task ReadThenCopyToAsyncWorks()
        {
            var data = Enumerable.Range(0, 1024).Select(b => (byte)b).ToArray();
            var inner = new MemoryStream(data);

            using var stream = new FileBufferingReadStream(inner, 1024 * 1024, bufferLimit: null, GetCurrentDirectory());

            var withoutBufferMs = new MemoryStream();
            var buffer = new byte[100];
            var read = stream.Read(buffer);
            await stream.CopyToAsync(withoutBufferMs);

            Assert.Equal(100, read);
            Assert.Equal(data.AsMemory(0, read).ToArray(), buffer);
            Assert.Equal(data.AsMemory(read).ToArray(), withoutBufferMs.ToArray());
        }

        [Fact]
        public async Task ReadThenSeekThenCopyToAsyncWorks()
        {
            var data = Enumerable.Range(0, 1024).Select(b => (byte)b).ToArray();
            var inner = new MemoryStream(data);

            using var stream = new FileBufferingReadStream(inner, 1024 * 1024, bufferLimit: null, GetCurrentDirectory());

            var withoutBufferMs = new MemoryStream();
            var buffer = new byte[100];
            var read = stream.Read(buffer);
            stream.Position = 0;
            await stream.CopyToAsync(withoutBufferMs);

            Assert.Equal(100, read);
            Assert.Equal(data.AsMemory(0, read).ToArray(), buffer);
            Assert.Equal(data.ToArray(), withoutBufferMs.ToArray());
        }

        [Fact]
        public void PartialReadThenSeekReplaysBuffer()
        {
            var data = Enumerable.Range(0, 1024).Select(b => (byte)b).ToArray();
            var inner = new MemoryStream(data);

            using var stream = new FileBufferingReadStream(inner, 1024 * 1024, bufferLimit: null, GetCurrentDirectory());

            var withoutBufferMs = new MemoryStream();
            var buffer = new byte[100];
            var read1 = stream.Read(buffer);
            stream.Position = 0;
            var buffer2 = new byte[200];
            var read2 = stream.Read(buffer2);
            Assert.Equal(100, read1);
            Assert.Equal(100, read2);
            Assert.Equal(data.AsMemory(0, read1).ToArray(), buffer);
            Assert.Equal(data.AsMemory(0, read2).ToArray(), buffer2.AsMemory(0, read2).ToArray());
        }

        [Fact]
        public async Task PartialReadAsyncThenSeekReplaysBuffer()
        {
            var data = Enumerable.Range(0, 1024).Select(b => (byte)b).ToArray();
            var inner = new MemoryStream(data);

            using var stream = new FileBufferingReadStream(inner, 1024 * 1024, bufferLimit: null, GetCurrentDirectory());

            var withoutBufferMs = new MemoryStream();
            var buffer = new byte[100];
            var read1 = await stream.ReadAsync(buffer);
            stream.Position = 0;
            var buffer2 = new byte[200];
            var read2 = await stream.ReadAsync(buffer2);
            Assert.Equal(100, read1);
            Assert.Equal(100, read2);
            Assert.Equal(data.AsMemory(0, read1).ToArray(), buffer);
            Assert.Equal(data.AsMemory(0, read2).ToArray(), buffer2.AsMemory(0, read2).ToArray());
        }

        [ConditionalFact]
        [OSSkipCondition(OperatingSystems.Windows, SkipReason = "UnixFileMode is not supported on Windows.")]
        public void Read_BufferingContentToDisk_CreatesFileWithUserOnlyUnixFileMode()
        {
            var inner = MakeStream(1024 * 2);
            string tempFileName;
            using (var stream = new FileBufferingReadStream(inner, 1024, null, GetCurrentDirectory()))
            {
                var bytes = new byte[1024 * 2];
                var read0 = stream.Read(bytes, 0, bytes.Length);
                Assert.Equal(bytes.Length, read0);
                Assert.Equal(read0, stream.Length);
                Assert.Equal(read0, stream.Position);
                Assert.False(stream.InMemory);
                Assert.NotNull(stream.TempFileName);

                var read1 = stream.Read(bytes, 0, bytes.Length);
                Assert.Equal(0, read1);

                tempFileName = stream.TempFileName!;
                Assert.True(File.Exists(tempFileName));

                //Assert.Equal(UnixFileMode.UserRead | UnixFileMode.UserWrite, File.GetUnixFileMode(tempFileName));
                var processStartInfo = new ProcessStartInfo
                {
                    FileName = "ls",
                    Arguments = $"-l {tempFileName}",
                    RedirectStandardOutput = true,
                    UseShellExecute = false
                };
                var process = Process.Start(processStartInfo);

                Assert.NotNull(process);
                var output = process!.StandardOutput.ReadToEnd();
                process.WaitForExit();
                Assert.StartsWith("-rw-------", output);
            }

            Assert.False(File.Exists(tempFileName));
        }

        private static string GetCurrentDirectory()
        {
            return AppContext.BaseDirectory;
        }

        private class NumberOfWritesMemoryStream : MemoryStream
        {
            public int NumberOfWrites { get; set; }

            public override void Write(byte[] buffer, int offset, int count)
            {
                NumberOfWrites++;
                base.Write(buffer, offset, count);
            }

            public override void Write(ReadOnlySpan<byte> source)
            {
                NumberOfWrites++;
                base.Write(source);
            }
        }
    }
}
