#include <time.h>
#ifdef _WIN32
#include <windows.h>
#else
#include <sys/time.h>
#include <unistd.h>
#endif
#include "../xyw.h"

/* clock device */
#define CLOCK_YEAR 0x0
#define CLOCK_MONTH 0x2
#define CLOCK_MONTHDAY 0x3
#define CLOCK_WEEKDAY 0x4
#define CLOCK_CLOCK_HOUR 0x5
#define CLOCK_MINUTE 0x6
#define CLOCK_SECOND 0x7
#define CLOCK_TIMER 0x8
#define CLOCK_ON_TIMER_ELAPSED 0xA

static int clock_timer_active = 0;
static int clock_timer_elapsed_pending = 0;

#ifdef _WIN32
static LARGE_INTEGER clock_timer_freq;
static LARGE_INTEGER clock_timer_target; // Target time when timer elapses
#else
static struct timespec clock_timer_target; // Target time when timer elapses
#endif

// Get current timer value (remaining ticks until target)
static xyw_word clock_get_timer_value(void)
{
    if (!clock_timer_active)
        return 0;

#ifdef _WIN32
    LARGE_INTEGER now;
    QueryPerformanceCounter(&now);
    // Calculate remaining time in 1/256 second units
    if (now.QuadPart >= clock_timer_target.QuadPart)
    {
        // Timer has elapsed
        clock_timer_active = 0;
        clock_timer_elapsed_pending = 1;
        return 0;
    }
    double remaining_sec = (double)(clock_timer_target.QuadPart - now.QuadPart) / clock_timer_freq.QuadPart;
    xyw_word remaining_ticks = (xyw_word)(remaining_sec * 256.0);
    if (remaining_ticks == 0)
    {
        // Less than 1 tick remaining, consider elapsed
        clock_timer_active = 0;
        clock_timer_elapsed_pending = 1;
        return 0;
    }
    return remaining_ticks;
#else
    struct timespec now;
    clock_gettime(CLOCK_MONOTONIC, &now);
    // Calculate remaining time in nanoseconds
    long long remaining_ns = (clock_timer_target.tv_sec - now.tv_sec) * 1000000000LL +
                             (clock_timer_target.tv_nsec - now.tv_nsec);
    if (remaining_ns <= 0)
    {
        // Timer has elapsed
        clock_timer_active = 0;
        clock_timer_elapsed_pending = 1;
        return 0;
    }
    // Convert to 1/256 second units (1/256 sec = 3906250 ns)
    xyw_word remaining_ticks = (xyw_word)(remaining_ns / 3906250);
    if (remaining_ticks == 0)
    {
        // Less than 1 tick remaining, consider elapsed
        clock_timer_active = 0;
        clock_timer_elapsed_pending = 1;
        return 0;
    }
    return remaining_ticks;
#endif
}

#define CLOCK_POLL_SLEEP_MS 100

int clock_poll(xyw_byte *data)
{
    xyw_word on_timer_handler = XYW_PEEKW(&data[CLOCK_ON_TIMER_ELAPSED]);
    if (!on_timer_handler)
        return 0; // no handler registered

    // Check if timer has elapsed (non-blocking)
    clock_get_timer_value();
    if (clock_timer_elapsed_pending)
    {
        clock_timer_elapsed_pending = 0;
        xyw_vm_set_running(1);
        xyw_vm_push_frame(XYW_DEVICE_AREA_START);
        *pc = on_timer_handler;
        return 1;
    }

    if (!clock_timer_active)
        return 0; // no timer running

    // Timer is active but hasn't elapsed yet — sleep briefly to avoid busy loop.
    // When terminal_poll is also active, it provides its own 100ms sleep via
    // getch_timeout, so this sleep only matters for timer-only programs.
#ifdef _WIN32
    Sleep(CLOCK_POLL_SLEEP_MS);
#else
    usleep((useconds_t)(CLOCK_POLL_SLEEP_MS * 1000));
#endif
    return -1; // active handler, no event yet
}

void clock_setup(xyw_byte *data)
{
    (void)data;
    clock_timer_active = 0;
    clock_timer_elapsed_pending = 0;
#ifdef _WIN32
    QueryPerformanceFrequency(&clock_timer_freq);
#endif
}

xyw_byte clock_input(xyw_byte *data, xyw_byte addr, xyw_byte *error)
{
    (void)error;
    (void)data;

    /* Handle timer reads */
    if (addr == CLOCK_TIMER)
    {
        xyw_word val = clock_get_timer_value();
        return (xyw_byte)(val >> 8);
    }
    if (addr == CLOCK_TIMER + 1)
    {
        xyw_word val = clock_get_timer_value();
        return (xyw_byte)(val & 0xFF);
    }
    // Reading CLOCK_ON_TIMER_ELAPSED blocks until timer elapses (if active)
    if (addr == CLOCK_ON_TIMER_ELAPSED)
    {
        // If timer is active, block until it elapses using absolute target time
        if (clock_timer_active)
        {
            xyw_word remaining = clock_get_timer_value();
            if (remaining > 0)
            {
#ifdef _WIN32
                // Calculate remaining time and sleep
                LARGE_INTEGER now;
                QueryPerformanceCounter(&now);
                if (clock_timer_target.QuadPart > now.QuadPart)
                {
                    double remaining_sec = (double)(clock_timer_target.QuadPart - now.QuadPart) / clock_timer_freq.QuadPart;
                    DWORD ms = (DWORD)(remaining_sec * 1000.0);
                    if (ms > 0)
                        Sleep(ms);
                }
#else
                // Use clock_nanosleep with absolute target time for precision
                clock_nanosleep(CLOCK_MONOTONIC, TIMER_ABSTIME, &clock_timer_target, NULL);
#endif
                // After sleep, update timer state
                clock_get_timer_value();
            }
        }
        // Return and clear the pending flag
        xyw_byte pending = clock_timer_elapsed_pending ? 1 : 0;
        clock_timer_elapsed_pending = 0;
        return pending;
    }

    time_t now = time(NULL);
    struct tm *lt = localtime(&now);
    if (!lt)
        return 0;

    switch (addr)
    {
    case CLOCK_YEAR:
        return (xyw_byte)((lt->tm_year + 1900) >> 8);
    case CLOCK_YEAR + 1:
        return (xyw_byte)((lt->tm_year + 1900) & 0xFF);
    case CLOCK_MONTH:
        // 1-12
        return (xyw_byte)(lt->tm_mon + 1);
    case CLOCK_MONTHDAY:
        // 1-31
        return (xyw_byte)lt->tm_mday;
    case CLOCK_WEEKDAY:
        // 0=Sunday ... 6=Saturday
        return (xyw_byte)lt->tm_wday;
    case CLOCK_CLOCK_HOUR:
        // 0-23
        return (xyw_byte)lt->tm_hour;
    case CLOCK_MINUTE:
        return (xyw_byte)lt->tm_min;
    case CLOCK_SECOND:
        return (xyw_byte)lt->tm_sec;
    default:
        return 0;
    }
}

void clock_output(xyw_byte *data, xyw_byte addr, xyw_byte *error)
{
    (void)error;

    /* When writing to CLOCK_TIMER+1 (check only last byte, so that this doesn't get fired twice, 
       once for each byte), start/restart the timer */
    if (addr == CLOCK_TIMER + 1)
    {
        // Read the full 16-bit timer value from device data
        xyw_word timer_val = XYW_PEEKW(&data[CLOCK_TIMER]);

        if (timer_val > 0)
        {
            clock_timer_active = 1;
            clock_timer_elapsed_pending = 0;
            // Calculate target time: now + timer_val * (1/256 second)
#ifdef _WIN32
            LARGE_INTEGER now;
            QueryPerformanceCounter(&now);
            // target = now + (timer_val / 256) seconds in performance counter units
            long long ticks_to_add = (long long)timer_val * clock_timer_freq.QuadPart / 256;
            clock_timer_target.QuadPart = now.QuadPart + ticks_to_add;
#else
            struct timespec now;
            clock_gettime(CLOCK_MONOTONIC, &now);
            // 1/256 second = 3906250 nanoseconds
            long long ns_to_add = (long long)timer_val * 3906250LL;
            clock_timer_target.tv_sec = now.tv_sec + (ns_to_add / 1000000000LL);
            clock_timer_target.tv_nsec = now.tv_nsec + (ns_to_add % 1000000000LL);
            // Handle nanosecond overflow
            if (clock_timer_target.tv_nsec >= 1000000000L)
            {
                clock_timer_target.tv_sec++;
                clock_timer_target.tv_nsec -= 1000000000L;
            }
#endif
        }
        else
        {
            // Writing 0 deactivates the timer
            clock_timer_active = 0;
            clock_timer_elapsed_pending = 0;
        }
    }
}