//
// Simple hack to change dpi on Logitech G400s
// G400s only support: 400, 800, 1600, 2000 and 4000 dpi, all other are interpolate by software
//
// Based on g400_hack from Przemek Aksamit
// https://bitbucket.org/extaliones/g400_hack/src
//
// gcc -lusb-1.0 -o g400s_hack g400s_hack.c
//

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <libusb-1.0/libusb.h>

#define G400S_VENDOR_ID   0x046d
#define G400S_PRODUCT_ID  0xc24c

#define EXIT_SUCCESS       0
#define EXIT_ERROR_ARGS    1
#define EXIT_ERROR_DEVICE  2
#define EXIT_ERROR_KERNEL  3
#define EXIT_ERROR_CLAIM   4
#define EXIT_ERROR_WRITE   5


libusb_context *ctx = NULL;
libusb_device_handle *handle = NULL;

int detached = 0;
int claimed  = 0;


void usage()
{
  printf("Usage: ./g400s_hack ( -400 | -800 | -1600 | -2000 | -4000 | -d | -n)\n");
  printf("Highly experimental, use with caution.\n");
}

void cleanup()
{
  if (claimed)
    libusb_release_interface(handle, 1);

  if (detached)
    libusb_attach_kernel_driver(handle, 1);

  libusb_close(handle);
  libusb_exit(ctx);
}

int main(int argc, char **argv)
{
  if (argc != 2 || argv[1][0] != '-') {
    usage();
    return EXIT_ERROR_ARGS;
  }

  //131 => 400dpi, 132 => 800dpi, 133 => 1600dpi, 134 => 2000dpi, 135 => 4000dpi
  uint16_t dpi_idx = 131;
  if      (strcmp(&argv[1][1], "400" ) == 0)
    dpi_idx += 0;
  else if (strcmp(&argv[1][1], "800" ) == 0)
    dpi_idx += 1;
  else if (strcmp(&argv[1][1], "1600") == 0)
    dpi_idx += 2;
  else if (strcmp(&argv[1][1], "2000") == 0)
    dpi_idx += 3;
  else if (strcmp(&argv[1][1], "4000") == 0)
    dpi_idx += 4;
  else if (strcmp(&argv[1][1], "d") == 0)
    dpi_idx = 0;
  else if (strcmp(&argv[1][1], "n") == 0)
    dpi_idx = 4;
  else {
    usage();
    return EXIT_ERROR_ARGS;
  }

  if (dpi_idx >= 131) {
    printf("Set new DPI: %s (index %i)\n", &argv[1][1], dpi_idx);
  }
  else {
    printf("Set Driver/Native mode: %s (index %i)\n", &argv[1][1], dpi_idx);
  }

  libusb_init(&ctx);

  handle = libusb_open_device_with_vid_pid(ctx, G400S_VENDOR_ID, G400S_PRODUCT_ID);
  libusb_set_debug(ctx, 3);

  if (!handle) {
    fprintf(stderr, "Logitech G400s not found! (Do you have usb rights? Try with sudo?)\n");
    cleanup();
    return EXIT_ERROR_DEVICE;
  }

  if (libusb_kernel_driver_active(handle, 1) == 1) {
    if (libusb_detach_kernel_driver(handle, 1) != 0) {
      fprintf(stderr, "Can't detach kernel driver.\n");
      cleanup();
      return EXIT_ERROR_KERNEL;
    }

    detached = 1;
  }

  if (libusb_claim_interface(handle, 1) != 0) {
    fprintf(stderr, "Failed to claim interface.\n");
    cleanup();
    return EXIT_ERROR_CLAIM;
  }

  claimed = 1;

  if (dpi_idx == 0) {
    // Set driver mode, then DPI to 400
    char data[2];
    data[0] = 0x20; data[1] = 0x01;
    int result = libusb_control_transfer (handle, 0x21, 9, 0x0320, 1, data, 2, 1000);
    if (result != 2) {
      fprintf(stderr, "Error writing to USB device (%d).\n", result);
      cleanup();
      return EXIT_ERROR_WRITE;
    }
    dpi_idx = 131;
  }

  if (libusb_control_transfer (handle, 0x40, 2, 0x008e, dpi_idx, NULL, 0, 1000) != 0) {
    fprintf(stderr, "Error writing to USB device.\n");
    cleanup();
    return EXIT_ERROR_WRITE;
  }

  cleanup();
  printf("Finished.\n");
  return EXIT_SUCCESS;
}