// mousectl - Swap mouse buttons from the macOS Terminal

// From https://superuser.com/a/1782251
//  with changes by taeber@rapczak.com

// Compile:
//   clang -framework IOKit -framework Foundation -o mousectl mousectl.c

#include <IOKit/hidsystem/IOHIDLib.h>
#include <IOKit/hidsystem/IOHIDParameter.h>
#include <IOKit/hidsystem/event_status_driver.h>
#include <stdbool.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

static char *describe(IOHIDButtonModes mode) {
  switch (mode) {
  case kIOHIDButtonMode_BothLeftClicks: // 0
    return "Both Left Clicks";
  case kIOHIDButtonMode_ReverseLeftRightClicks: // 1
    return "Reverse Left Right Clicks";
  case kIOHIDButtonMode_EnableRightClick: // 2
    return "Enable Right Click";
  default:
    return "<unknown>";
  }
}

static bool GetButtonMode(io_connect_t handle, IOHIDButtonModes *mode) {
  kern_return_t ret;
  IOByteCount actualSize;
  ret = IOHIDGetParameter(handle, CFSTR(kIOHIDPointerButtonMode), sizeof *mode,
                          mode, &actualSize);
  if (ret != KERN_SUCCESS) {
    fprintf(stderr, "Error! IOHIDGetParameter failed: %d.\n", ret);
    return false;
  }

  if (actualSize != sizeof *mode) {
    // TODO: maybe currentButtonStatus should be void* with an explicit cast
    // to IOHIDButtonModes
    fprintf(
        stderr,
        "Warning! IOHIDGetParameter returned unexpected actualSize! (Got %d; "
        "wanted %ld)\n",
        (int)actualSize, sizeof *mode);
  }

  return true;
}

static bool SetButtonMode(io_connect_t handle, IOHIDButtonModes newMode) {
  kern_return_t ret;
  IOByteCount actualSize;
  ret = IOHIDSetParameter(handle, CFSTR(kIOHIDPointerButtonMode), &newMode,
                          sizeof newMode);
  if (ret != KERN_SUCCESS) {
    fprintf(stderr, "Error! IOHIDSetParameter failed: %d\n", ret);
    return ret;
  }
  return true;
}

static int print(io_connect_t handle) {
  IOHIDButtonModes buttonMode;
  if (!GetButtonMode(handle, &buttonMode))
    return 1;

  printf("Current mouse button mode: %s\n", describe(buttonMode));
  return 0;
}

static int swap(io_connect_t handle) {
  IOHIDButtonModes currentButtonStatus;
  if (!GetButtonMode(handle, &currentButtonStatus))
    return 1;

  IOHIDButtonModes newButtonStatus;
  switch (currentButtonStatus) {
  case kIOHIDButtonMode_BothLeftClicks:         // 0
  case kIOHIDButtonMode_ReverseLeftRightClicks: // 1
    newButtonStatus = kIOHIDButtonMode_EnableRightClick;
    break;
  case kIOHIDButtonMode_EnableRightClick: // 2
    newButtonStatus = kIOHIDButtonMode_ReverseLeftRightClicks;
    break;
  default:
    fprintf(stderr, "Unknown IOHIDButtonModes value: %d\n",
            currentButtonStatus);
    return 1;
  }

  if (!SetButtonMode(handle, newButtonStatus))
    return 1;

  printf("New mouse button mode is : %s\n", describe(newButtonStatus));
  printf("Old mouse button mode was: %s\n", describe(currentButtonStatus));

  return 0;
}

static char cmd[] = "mousectl";

static int usage(bool helpWanted) {
  FILE *fp = helpWanted ? stdout : stderr;
  fprintf(fp, "Usage: %s <subcommand>\n\n", cmd);
  fprintf(fp, "%s\n", "Subcommands:");
  fprintf(fp, "%s\n", "\tprint  Prints the current mouse button mode.");
  fprintf(fp, "%s\n", "\tswap   Swaps mouse buttons.");
  fprintf(fp, "%s\n", "\thelp   Prints this usage.");
  return helpWanted ? 0 : 1;
}

int main(int argc, char *argv[]) {
  if (argc <= 0)
    return 42;

  if (argc == 1)
    return usage(false);

  char *subcmd = argv[1];
  int (*sub)(io_connect_t);
  if (strcmp("print", subcmd) == 0) {
    sub = print;
  } else if (strcmp("swap", subcmd) == 0) {
    sub = swap;
  } else if (strcmp("help", subcmd) == 0 || strcmp("-h", subcmd) == 0 ||
             strcmp("-help", subcmd) == 0 || strcmp("--help", subcmd) == 0 ||
             strcmp("/?", subcmd) == 0) {
    return usage(true);
  } else {
    fprintf(stderr, "Error! Unrecognized subcommand: %s\n", subcmd);
    return usage(false);
  }

  io_connect_t handle = NXOpenEventStatus();
  if (!handle) {
    fprintf(stderr, "%s\n", "NXOpenEventStatus failed!");
    return 1;
  }

  int ret = sub(handle);
  NXCloseEventStatus(handle);

  return ret;
}