basic-computer-games/58_Love/csharp/SourceCharacters.cs

using System;

namespace Love;

internal class SourceCharacters
{
    private readonly int _lineLength;
    private readonly char[][] _chars;
    private int _currentRow;
    private int _currentIndex;

    public SourceCharacters(int lineLength, string message)
    {
        _lineLength = lineLength;
        _chars = new[] { new char[lineLength], new char[lineLength] };

        for (int i = 0; i < lineLength; i++)
        {
            _chars[0][i] = message[i % message.Length];
            _chars[1][i] = ' ';
        }
    }

    public ReadOnlySpan<char> GetCharacters(int count)
    {
        var span = new ReadOnlySpan<char>(_chars[_currentRow], _currentIndex, count);

        _currentRow = 1 - _currentRow;
        _currentIndex += count;
        if (_currentIndex >= _lineLength)
        {
            _currentIndex = _currentRow = 0;
        }

        return span;
    }
}