/// <summary>
///     Snapshot-based undo/redo history for JSON editing.
///     Stores full JSON strings, capped at a maximum number of entries and a maximum total size.
/// </summary>
/// <param name = "maxSnapshots">The most snapshots to keep.</param>
/// <param name = "maxTotalChars">
///     The most characters to keep across all snapshots. Fifty copies of a large document would otherwise
///     hold several GB for every open viewer. The current snapshot and the one before it are always kept.
/// </param>
public sealed class EditHistory(int maxSnapshots = 50, long maxTotalChars = 256 * 1024 * 1024)
{
    public bool CanUndo => _currentIndex > 0;
    public bool CanRedo => _currentIndex < _snapshots.Count - 1;

    public void PushSnapshot(string json)
    {
        ArgumentNullException.ThrowIfNull(json);
        // Truncate any redo entries beyond current position
        if (_currentIndex < _snapshots.Count - 1)
        {
            for (int i = _currentIndex + 1; i < _snapshots.Count; i++)
            {
                _totalChars -= _snapshots[i].Length;
            }

            _snapshots.RemoveRange(_currentIndex + 1, _snapshots.Count - _currentIndex - 1);
        }

        _snapshots.Add(json);
        _totalChars += json.Length;
        _currentIndex = _snapshots.Count - 1;
        while (_snapshots.Count > 2 && (_snapshots.Count > maxSnapshots || _totalChars > maxTotalChars))
        {
            _totalChars -= _snapshots[0].Length;
            _snapshots.RemoveAt(0);
            _currentIndex--;
        }
    }

    public string? Undo()
    {
        if (!CanUndo)
        {
            return null;
        }

        _currentIndex--;
        return _snapshots[_currentIndex];
    }

    public string? Redo()
    {
        if (!CanRedo)
        {
            return null;
        }

        _currentIndex++;
        return _snapshots[_currentIndex];
    }

    public void Clear()
    {
        _snapshots.Clear();
        _totalChars = 0;
        _currentIndex = -1;
    }
}