barcode-host/Shared/KeyboardMouse/InputReader.cs

using Microsoft.Extensions.Logging;

namespace Barcode.Host.Shared.KeyboardMouse;

public class InputReader : IDisposable
{
    private readonly ILogger<InputReader> _Logger;
    private const int _BufferLength = 24;

    private static readonly int _PiOffset;

    private readonly byte[] _Buffer = new byte[_BufferLength];

    private FileStream? _Stream;
    private bool _Disposing;

    public delegate void RaiseKeyPress(KeyPressEvent e);

    public delegate void RaiseMouseMove(MouseMoveEvent e);

    public event RaiseKeyPress? OnKeyPress;

    public event RaiseMouseMove? OnMouseMove;

    public string Path { get; }

    public bool Faulted { get; private set; }

    static InputReader()
    {
        if (RunningOnRaspberryPi())
        {
            _PiOffset = -8;
        }
    }

    public InputReader(
        string path,
        ILogger<InputReader> logger)
    {
        _Logger = logger;

        Path = path;

        try
        {
            _Stream = new FileStream(path, FileMode.Open, FileAccess.Read, FileShare.ReadWrite);
        }
        catch (UnauthorizedAccessException ex)
        {
            _Logger.LogError(ex, "Current user doesn't have permissions to access input data. Add user to input group to correct this error");
            Faulted = true;
        }
        catch (IOException ex)
        {
            _Logger.LogWarning(ex, $"Error occurred while trying to build stream for {path}");
            Faulted = true;
        }

        _ = Task.Run(Run);
    }

    private void Run()
    {
        while (true)
        {
            if (_Disposing)
                break;

            try
            {
                if (!Faulted && _Stream is not null)
                {
                    _ = _Stream.Read(_Buffer, 0, _BufferLength);
                }
            }
            catch (IOException ex)
            {
                _Logger.LogInformation(ex, $"Error occured while trying to read from the stream for {Path}");
                Faulted = true;
            }

            EventType type = GetEventType();
            short code = GetCode();
            int value = GetValue();

            switch (type)
            {
                case EventType.EV_KEY:
                    HandleKeyPressEvent(code, value);
                    break;
                case EventType.EV_REL:
                    MouseAxis axis = (MouseAxis)code;
                    MouseMoveEvent e = new(axis, value);
                    OnMouseMove?.Invoke(e);
                    break;
            }
        }
    }

    private int GetValue()
    {
        byte[] valueBits = new[]
        {
            _Buffer[20 + _PiOffset],
            _Buffer[21 + _PiOffset],
            _Buffer[22 + _PiOffset],
            _Buffer[23 + _PiOffset]
        };

        int value = BitConverter.ToInt32(valueBits, 0);

        return value;
    }

    private short GetCode()
    {
        byte[] codeBits = new[]
        {
            _Buffer[18 + _PiOffset],
            _Buffer[19 + _PiOffset]
        };

        short code = BitConverter.ToInt16(codeBits, 0);

        return code;
    }

    private EventType GetEventType()
    {
        byte[] typeBits = new[]
        {
            _Buffer[16 + _PiOffset],
            _Buffer[17 + _PiOffset]
        };

        short type = BitConverter.ToInt16(typeBits, 0);

        EventType eventType = (EventType)type;

        return eventType;
    }

    private void HandleKeyPressEvent(short code, int value)
    {
        EventCode c = (EventCode)code;
        KeyState s = (KeyState)value;
        KeyPressEvent e = new(c, s);
        OnKeyPress?.Invoke(e);
    }

    public void Dispose()
    {
        _Disposing = true;
        _Stream?.Dispose();
        _Stream = null;
    }

    private static bool RunningOnRaspberryPi()
    {
        string path = "/proc/cpuinfo";
        string[] text = File.ReadAllLines(path);
        bool runningOnPi = text.Any(l => l.Contains("Raspberry Pi"));
        return runningOnPi;
    }
}