/* numlock_debug.c */
#include <windows.h>
#include <stdio.h>
#include <time.h>

/* Global hook handle so we can unhook on exit */
static HHOOK g_hHook = NULL;

/* Print timestamp like "[12:34:56] " for log readability */
static void PrintTimeStamp(void)
{
    time_t t = time(NULL);
    struct tm *tm_info = localtime(&t);
    if (tm_info) {
        printf("[%02d:%02d:%02d] ",  // HH:MM:SS timestamp
               tm_info->tm_hour,
               tm_info->tm_min,
               tm_info->tm_sec);
    } else {
        printf("[??:??:??] ");
    }
}

/*
 * Low-level keyboard hook callback.
 * We only care about VK_NUMLOCK key-up events to capture the
 * state *after* the toggle has occurred.
 */
static LRESULT CALLBACK LowLevelKeyboardProc(int nCode, WPARAM wParam, LPARAM lParam)
{
    /* If this is not an action event or not a key-up, pass along immediately */
    if (nCode != HC_ACTION || wParam != WM_KEYUP) {
        return CallNextHookEx(g_hHook, nCode, wParam, lParam);
    }

    KBDLLHOOKSTRUCT *p = (KBDLLHOOKSTRUCT *)lParam;
    /* Ignore all keys except NumLock */
    if (p->vkCode != VK_NUMLOCK) {
        return CallNextHookEx(g_hHook, nCode, wParam, lParam);
    }

    /* Single-line detailed log:
     * nCode: hook result code
     * wParam: message (e.g., WM_KEYUP)
     * vk, sc, fl: virtual key, scan code, flags
     * raw: raw GetKeyState result (16-bit)
     * ON/OFF: computed toggle state
     */
    PrintTimeStamp();
    SHORT rawState = GetKeyState(VK_NUMLOCK);
    int toggled = rawState & 0x0001;  /* bit0: 1 if toggle state is ON */

    /*
     * Mask with 0xFFFF to avoid sign-extension when printing
     * GetKeyState returns a signed SHORT but printf promotes
     * arguments to 32-bit int, so a negative value (0x8001) becomes
     * 0xFFFF8001 without masking.
     */
    printf("nCode=%d wParam=0x%04X vk=0x%02X sc=0x%02X fl=0x%02X raw=0x%04hX => %s\n",
           nCode,
           (unsigned)wParam,
           (unsigned)p->vkCode,
           (unsigned)p->scanCode,
           (unsigned)p->flags,
           rawState & 0xFFFF,  /* show only lower 16 bits */
           toggled ? "ON" : "OFF");

    /* Continue the hook chain */
    return CallNextHookEx(g_hHook, nCode, wParam, lParam);
}

int main(void)
{
    MSG msg;

    /* Install the low-level keyboard hook in our process.
     * WH_KEYBOARD_LL captures all keyboard events globally.
     */
    g_hHook = SetWindowsHookEx(
        WH_KEYBOARD_LL,
        LowLevelKeyboardProc,
        GetModuleHandle(NULL),
        0
    );
    if (!g_hHook) {
        fprintf(stderr, "ERROR: SetWindowsHookEx failed (%lu)\n",
                (unsigned long)GetLastError());
        return 1;
    }

    PrintTimeStamp();
    printf("NumLock debug monitor started. Press NumLock to log state. Ctrl+C to exit.\n");

    /* Standard message loop to keep the hook alive */
    while (GetMessage(&msg, NULL, 0, 0)) {
        TranslateMessage(&msg);
        DispatchMessage(&msg);
    }

    /* Uninstall hook and exit cleanly */
    UnhookWindowsHookEx(g_hHook);
    return 0;
}