spectre.console/src/Spectre.Console.Cli/Internal/TextBuffer.cs

namespace Spectre.Console.Cli;

internal sealed class TextBuffer : IDisposable
{
    // There is some kind of bug
    private readonly StringReader _reader;

    public bool ReachedEnd => _reader.Peek() == -1;
    public string Original { get; }
    public int Position { get; private set; }

    public TextBuffer(string text)
    {
        _reader = new StringReader(text);
        Original = text;
        Position = 0;
    }

    public TextBuffer(TextBuffer? buffer, string text)
    {
        _reader = new StringReader(text);
        Original = buffer != null ? buffer.Original + " " + text : text;
        Position = buffer?.Position + 1 ?? 0;
    }

    public void Dispose()
    {
        _reader.Dispose();
    }

    public char Peek()
    {
        return (char)_reader.Peek();
    }

    public bool TryPeek(out char character)
    {
        var value = _reader.Peek();
        if (value == -1)
        {
            character = '\0';
            return false;
        }

        character = (char)value;
        return true;
    }

    public void Consume()
    {
        EnsureNotAtEnd();
        Read();
    }

    public void Consume(char character)
    {
        EnsureNotAtEnd();
        if (Read() != character)
        {
            throw new InvalidOperationException($"Expected '{character}' token.");
        }
    }

    public bool IsNext(char character)
    {
        if (TryPeek(out var result))
        {
            return result == character;
        }

        return false;
    }

    public char Read()
    {
        EnsureNotAtEnd();
        var result = (char)_reader.Read();
        Position++;
        return result;
    }

    private void EnsureNotAtEnd()
    {
        if (ReachedEnd)
        {
            throw new InvalidOperationException("Can't read past the end of the buffer.");
        }
    }
}