using System.Text;

namespace Agent.App.Logging;

internal sealed class RollingFileWriter : IDisposable
{
    private readonly object _sync = new();
    private readonly string _path;
    private readonly long _maxBytes;
    private readonly int _retainedFiles;
    private StreamWriter _writer;

    public RollingFileWriter(string path, long maxBytes, int retainedFiles)
    {
        _path = path;
        _maxBytes = maxBytes;
        _retainedFiles = retainedFiles;
        Directory.CreateDirectory(Path.GetDirectoryName(path)!);
        _writer = Open();
    }

    public void WriteLine(string line)
    {
        lock (_sync)
        {
            if (_writer.BaseStream.Length >= _maxBytes) Rotate();
            _writer.WriteLine(line);
            _writer.Flush();
        }
    }

    private StreamWriter Open() => new(new FileStream(_path, FileMode.Append, FileAccess.Write, FileShare.Read), new UTF8Encoding(false));

    private void Rotate()
    {
        _writer.Dispose();
        for (int index = _retainedFiles - 1; index >= 1; index--)
        {
            string source = $"{_path}.{index}";
            if (File.Exists(source)) File.Move(source, $"{_path}.{index + 1}", true);
        }
        if (File.Exists(_path)) File.Move(_path, $"{_path}.1", true);
        _writer = Open();
    }

    public void Dispose()
    {
        lock (_sync) _writer.Dispose();
    }
}