using System.Runtime.InteropServices;

namespace RobotNet10.RobotApp.Natives;

/// <summary>
/// Native declarations for Linux evdev (event device) input subsystem.
/// Used for low-latency keyboard input reading from /dev/input/event* devices.
/// </summary>
internal static partial class EvdevNative
{
    // Event types
    public const ushort EV_SYN = 0x00;
    public const ushort EV_KEY = 0x01;
    public const ushort EV_REL = 0x02;
    public const ushort EV_ABS = 0x03;

    // Key event values
    public const int KEY_RELEASE = 0;
    public const int KEY_PRESS = 1;
    public const int KEY_REPEAT = 2;

    // Linux key codes (from input-event-codes.h)
    public const ushort KEY_ESC = 1;
    public const ushort KEY_MINUS = 12;
    public const ushort KEY_EQUAL = 13;
    public const ushort KEY_Q = 16;
    public const ushort KEY_W = 17;
    public const ushort KEY_E = 18;
    public const ushort KEY_A = 30;
    public const ushort KEY_S = 31;
    public const ushort KEY_D = 32;
    public const ushort KEY_Z = 44;
    public const ushort KEY_C = 46;
    public const ushort KEY_SPACE = 57;
    public const ushort KEY_KPMINUS = 74;
    public const ushort KEY_KPPLUS = 78;

    // ioctl constants for evdev
    // EVIOCGNAME(len): Get device name
    // Calculated as: _IOC(_IOC_READ, 'E', 0x06, len)
    // where _IOC_READ=2, 'E'=0x45
    // Formula: (2<<30) | (0x45<<8) | (0x06) | (256<<16) = 0x80FF4506
    public const uint EVIOCGNAME_256 = 0x80FF4506;

    // File open flags
    public const int O_RDONLY = 0x0000;
    public const int O_NONBLOCK = 0x0800;

    // Error codes
    public const int EAGAIN = 11;
    public const int EACCES = 13;

    /// <summary>
    /// Linux input event structure (24 bytes on 64-bit systems)
    /// Represents a single input event from evdev
    /// </summary>
    [StructLayout(LayoutKind.Sequential)]
    public struct input_event
    {
        public long tv_sec;      // timestamp seconds
        public long tv_usec;     // timestamp microseconds
        public ushort type;      // event type (EV_KEY, EV_REL, etc.)
        public ushort code;      // event code (KEY_W, KEY_A, etc.)
        public int value;        // event value (0=release, 1=press, 2=repeat)
    }

    // File operations for evdev
    /// <summary>
    /// Open a file and return a file descriptor
    /// </summary>
    [LibraryImport("libc", SetLastError = true, StringMarshalling = StringMarshalling.Utf8)]
    public static partial int open(string pathname, int flags);

    /// <summary>
    /// Close a file descriptor
    /// </summary>
    [LibraryImport("libc", SetLastError = true)]
    public static partial int close(int fd);

    /// <summary>
    /// Read from a file descriptor into input_event buffer
    /// </summary>
    [LibraryImport("libc", SetLastError = true)]
    public static partial int read(int fd, ref input_event buf, int count);

    /// <summary>
    /// ioctl system call for device control
    /// Used to query device name via EVIOCGNAME
    /// </summary>
    [LibraryImport("libc", SetLastError = true)]
    public static partial int ioctl(int fd, uint request, byte[] argp);

    // Error handling
    /// <summary>
    /// Get pointer to errno location
    /// </summary>
    [LibraryImport("libc")]
    public static partial IntPtr __errno_location();

    /// <summary>
    /// Get last error number (errno)
    /// </summary>
    public static int GetLastError()
    {
        IntPtr errnoPtr = __errno_location();
        if (errnoPtr == IntPtr.Zero)
        {
            return 0;
        }
        return Marshal.ReadInt32(errnoPtr);
    }
}