/* Copyright (c) Robert Walker, support@tunesmithy.co.uk
 * Free source. Do what you wish with it - treat it as you would
 * example code in a book on c programming.
 */
#include "time64.h"
#undef time
#undef localtime
#undef mktime
#undef difftime
#undef gmtime
#undef time_t

#include <assert.h>
#include <time.h>
#include <windows.h>

#define SECS_TO_FT_MULT 10000000
#ifdef _DEBUG
#    define DEBUG_TIME_T
#endif

/* From MSVC help:
 * The gmtime, mktime, and localtime functions use the same single,
 * statically allocated structure to hold their results. Each call to
 * one of these functions destroys the result of any previous call.
 * If timer represents a date before midnight, January 1, 1970,
 * gmtime returns NULL. There is no error return.
 *
 * So here is the struct to use for our 64 bit implementation
 *
 * However, it may be useful to be able to make this thread safe
 */

#ifdef USE_THREAD_LOCAL_VARIABLES
#    define TIME64_THREAD_LOCAL _declspec(thread)
#else
#    define TIME64_THREAD_LOCAL
#endif

TIME64_THREAD_LOCAL static struct tm today_ret;

static void T64ToFileTime(t64 *pt, FILETIME *pft) {
    LARGE_INTEGER li;
    li.QuadPart = *pt * SECS_TO_FT_MULT;
    pft->dwLowDateTime = li.LowPart;
    pft->dwHighDateTime = li.HighPart;
}

static void FileTimeToT64(FILETIME *pft, t64 *pt) {
    LARGE_INTEGER li;
    li.LowPart = pft->dwLowDateTime;
    li.HighPart = pft->dwHighDateTime;
    *pt = li.QuadPart;
    *pt /= SECS_TO_FT_MULT;
}

//#define  FindTimeTBase() ((t64) 11644473600)
#define FindTimeTBase() (((__int64)11644) * 1000000 + 473600)

// calculated using
/**
    static t64 FindTimeTBase(void)
    {
    // Find 1st Jan 1970 as a FILETIME
    SYSTEMTIME st;
    FILETIME ft;
    memset(&st,0,sizeof(st));
    st.wYear=1970;
    st.wMonth=1;
    st.wDay=1;
    SystemTimeToFileTime(&st, &ft);
    FileTimeToT64(&ft,&tbase);
    return tbase;
    }
**/

static void SystemTimeToT64(SYSTEMTIME *pst, t64 *pt) {
    FILETIME ft;
    SystemTimeToFileTime(pst, &ft);
    FileTimeToT64(&ft, pt);
    *pt -= FindTimeTBase();
}

static void T64ToSystemTime(t64 *pt, SYSTEMTIME *pst) {
    FILETIME ft;
    t64 t = *pt;
    t += FindTimeTBase();
    T64ToFileTime(&t, &ft);
    FileTimeToSystemTime(&ft, pst);
}

t64 time_64(t64 *pt) {
    t64 t;
    SYSTEMTIME st;
    GetSystemTime(&st);
    SystemTimeToT64(&st, &t);
#ifdef DEBUG_TIME_T
    {
        time_t t2 = time(NULL);
        if (t2 >= 0)

            // 2005 assert(abs(t2-(int)t)<=1);
            assert(abs((long)(t2 - (int)t)) <= 1);

        // the <=1 here is in case the seconds get incremented
        // betweeen the GetSystemTime(..) call and the time(..) call
    }
#endif
    if (pt)
        *pt = t;
    return t;
}

double difftime_64(t64 time1, t64 time0) { return (double)(time1 - time0); }

t64 mktime64(struct tm *today) {
    t64 t;
    SYSTEMTIME st;
    st.wDay = (WORD)today->tm_mday;
    st.wDayOfWeek = (WORD)today->tm_wday;
    st.wHour = (WORD)today->tm_hour;
    st.wMinute = (WORD)today->tm_min;
    st.wMonth = (WORD)(today->tm_mon + 1);
    st.wSecond = (WORD)today->tm_sec;
    st.wYear = (WORD)(today->tm_year + 1900);
    st.wMilliseconds = 0;
    SystemTimeToT64(&st, &t);
    return t;
}

#define DAY_IN_SECS (60 * 60 * 24)
struct tm *gmtime_64(t64 t) {
    SYSTEMTIME st;
    T64ToSystemTime(&t, &st);
    today_ret.tm_wday = st.wDayOfWeek;
    today_ret.tm_min = st.wMinute;
    today_ret.tm_sec = st.wSecond;
    today_ret.tm_mon = st.wMonth - 1;
    today_ret.tm_mday = st.wDay;
    today_ret.tm_hour = st.wHour;
    today_ret.tm_year = st.wYear - 1900;
    {
        SYSTEMTIME styear;
        t64 t64Year;
        memset(&styear, 0, sizeof(styear));
        styear.wYear = st.wYear;
        styear.wMonth = 1;
        styear.wDay = 1;
        SystemTimeToT64(&styear, &t64Year);
        today_ret.tm_yday = (int)((t - t64Year) / DAY_IN_SECS);
    }
    today_ret.tm_isdst = 0;
#ifdef DEBUG_TIME_T
    {
        struct tm today2;
        long t32 = (int)t;
        if (t32 >= 0) {
            // 2005   today2=*gmtime(&t32);
            today2 = *gmtime((time_t *)&t32);

            assert(today_ret.tm_yday == today2.tm_yday);
            assert(today_ret.tm_wday == today2.tm_wday);
            assert(today_ret.tm_min == today2.tm_min);
            assert(today_ret.tm_sec == today2.tm_sec);
            assert(today_ret.tm_mon == today2.tm_mon);
            assert(today_ret.tm_mday == today2.tm_mday);
            assert(today_ret.tm_hour == today2.tm_hour);
            assert(today_ret.tm_year == today2.tm_year);
        }
    }
    {
        t64 t2 = mktime64(&today_ret);
        assert(t2 == t);
    }
#endif
    return &today_ret;
}

struct tm *localtime_64(t64 *pt) {
    t64 t = *pt;
    FILETIME ft, ftlocal;
    T64ToFileTime(&t, &ft);
    FileTimeToLocalFileTime(&ft, &ftlocal);
    FileTimeToT64(&ftlocal, &t);
    today_ret = *gmtime_64(t);
    {
        TIME_ZONE_INFORMATION TimeZoneInformation;
        switch (GetTimeZoneInformation(&TimeZoneInformation)) {
        case TIME_ZONE_ID_DAYLIGHT:
            today_ret.tm_isdst = 1;
            break;
        case TIME_ZONE_ID_STANDARD:
            today_ret.tm_isdst = 0;
            break;
        case TIME_ZONE_ID_UNKNOWN:
            today_ret.tm_isdst = -1;
            break;
        }
    }
    return &today_ret;
}