using System;
using System.IO;

namespace AspClassic.Scripting.Utils;

public sealed class ConsoleInputStream : Stream
{
	private const int MinimalBufferSize = 4096;

	public static readonly ConsoleInputStream Instance = new ConsoleInputStream();

	private readonly Stream _input;

	private readonly object _lock = new object();

	private readonly byte[] _buffer = new byte[4096];

	private int _bufferPos;

	private int _bufferSize;

	public override bool CanRead => true;

	public override bool CanSeek => false;

	public override bool CanWrite => false;

	public override long Length
	{
		get
		{
			throw new NotSupportedException();
		}
	}

	public override long Position
	{
		get
		{
			throw new NotSupportedException();
		}
		set
		{
			throw new NotSupportedException();
		}
	}

	private ConsoleInputStream()
	{
		_input = Console.OpenStandardInput();
	}

	public override int Read(byte[] buffer, int offset, int count)
	{
		lock (_lock)
		{
			int num;
			if (_bufferSize > 0)
			{
				num = Math.Min(count, _bufferSize);
				Buffer.BlockCopy(_buffer, _bufferPos, buffer, offset, num);
				_bufferPos += num;
				_bufferSize -= num;
				offset += num;
				count -= num;
			}
			else
			{
				num = 0;
			}
			if (count > 0)
			{
				if (count < 4096)
				{
					int num2 = _input.Read(_buffer, 0, 4096);
					int num3 = Math.Min(num2, count);
					Buffer.BlockCopy(_buffer, 0, buffer, offset, num3);
					_bufferSize = num2 - num3;
					_bufferPos = num3;
					return num + num3;
				}
				return num + _input.Read(buffer, offset, count);
			}
			return num;
		}
	}

	public override void Flush()
	{
		throw new NotSupportedException();
	}

	public override long Seek(long offset, SeekOrigin origin)
	{
		throw new NotSupportedException();
	}

	public override void SetLength(long value)
	{
		throw new NotSupportedException();
	}

	public override void Write(byte[] buffer, int offset, int count)
	{
		throw new NotSupportedException();
	}
}