#include <iostream.h>
#include <dos.h>
#include <conio.h>
#include <string.h>
#include <stdlib.h>

//----------------------------------------------------------------------------

unsigned char value = 0;
unsigned int mode = 0; // 0: standard mode, 1: enhanced mode

void interrupt (*OldHandler08H)(...);
void interrupt (*OldHandler09H)(...);

//----------------------------------------------------------------------------

void itoa(unsigned int value, char* str, int base)
{
    char* p = str;
    char* p1, * p2;
    unsigned int digits = 0;

    do {
        unsigned int remainder = value % base;
        *p++ = (remainder < 10) ? '0' + remainder : 'A' + remainder - 10;
        digits++;
        value /= base;
    } while (value != 0);

    *p = '\0';

    // Reverse the string
    p1 = str;
    p2 = p - 1;
    while (p1 < p2) {
        char tmp = *p1;
        *p1 = *p2;
        *p2 = tmp;
        p1++;
        p2--;
    }
}

//----------------------------------------------------------------------------

void interrupt NewHandler08H(...)
{
    char text[16];
    int i;
    for (i = 0; i < 15; i++)
        text[i] = ' ';
    text[15] = 0;

    if (mode == 0) {
        struct dostime_t tm;
        _dos_gettime(&tm);
        itoa(tm.hour, text, 10);
        strcat(text, ":");
        itoa(tm.minute, text + strlen(text), 10);
        strcat(text, ":");
        itoa(tm.second, text + strlen(text), 10);
    } else {
        itoa(value, text, 10);
    }

    text[strlen(text)] = ' ';
    for (i = 0; i < strlen(text); i++)
        pokeb(0xB800, 12 * 160 + (40 + i) * 2, text[i]);

    value++;
    outp(0x20, 0x20);

    if (kbhit() && getch() == 27) // Check for Esc key press
        exit(0);
}

//----------------------------------------------------------------------------

void interrupt NewHandler09H(...)
{
    asm sti
    int i;
    if (inp(0x60) == 0x58) // Check for F12 key press
    {
        mode = 1 - mode; // Toggle mode between standard and enhanced
        clrscr();
    }
    OldHandler09H();
}

//----------------------------------------------------------------------------

int main()
{
    textcolor(LIGHTGRAY);
    textbackground(BLACK);
    _setcursortype(_NOCURSOR);
    clrscr();

    OldHandler08H = getvect(0x08);
    OldHandler09H = getvect(0x09);

    setvect(0x08, NewHandler08H);
    setvect(0x09, NewHandler09H);

    while (kbhit())
        getch();

    getch();

    setvect(0x08, OldHandler08H);
    setvect(0x09, OldHandler09H);

    _setcursortype(_NORMALCURSOR);
    clrscr();

    return 0;
}