dosdatetime.cpp

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/*
  Zipios -- a small C++ library that provides easy access to .zip files.

  Copyright (C) 2019  Made to Order Software Corporation

  This library is free software; you can redistribute it and/or
  modify it under the terms of the GNU Lesser General Public
  License as published by the Free Software Foundation; either
  version 2.1 of the License, or (at your option) any later version.

  This library is distributed in the hope that it will be useful,
  but WITHOUT ANY WARRANTY; without even the implied warranty of
  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  Lesser General Public License for more details.

  You should have received a copy of the GNU Lesser General Public
  License along with this library; if not, write to the Free Software
  Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301  USA
*/

#include "zipios/dosdatetime.hpp"

#include "zipios/zipiosexceptions.hpp"


namespace zipios
{


DOSDateTime::dosdatetime_t const  DOSDateTime::g_min_dosdatetime;     // Jan  1, 1980  00:00:00
DOSDateTime::dosdatetime_t const  DOSDateTime::g_max_dosdatetime;     // Dec 31, 2107  23:59:59




union dosdatetime_convert_t
{
    DOSDateTime::dosdatetime_t      m_dosdatetime;
    struct fields
    {
        DOSDateTime::dosdatetime_t      m_second : 5;   // WARNING: the precision is every 2 seconds (0, 2, 4, etc.)
        DOSDateTime::dosdatetime_t      m_minute : 6;
        DOSDateTime::dosdatetime_t      m_hour   : 5;
        DOSDateTime::dosdatetime_t      m_mday   : 5;  // 1 to 31
        DOSDateTime::dosdatetime_t      m_month  : 4;  // 1 to 12
        DOSDateTime::dosdatetime_t      m_year   : 7;  // add 1980
    } m_fields;
};



namespace
{

int const g_days_in_month[12] = {
    /* Jan */   31,
    /* Feb */   0, // special handling
    /* Mar */   31,
    /* Apr */   30,
    /* May */   31,
    /* Jun */   30,
    /* Jul */   31,
    /* Aug */   31,
    /* Sep */   30,
    /* Oct */   31,
    /* Nov */   30,
    /* Dec */   31
};


int const g_ydays[12] = {
    /* Jan */   0,
    /* Feb */   31,
    /* Mar */   31 + 0, // special handling
    /* Apr */   31 + 0 + 31,
    /* May */   31 + 0 + 31 + 30,
    /* Jun */   31 + 0 + 31 + 30 + 31,
    /* Jul */   31 + 0 + 31 + 30 + 31 + 30,
    /* Aug */   31 + 0 + 31 + 30 + 31 + 30 + 31,
    /* Sep */   31 + 0 + 31 + 30 + 31 + 30 + 31 + 31,
    /* Oct */   31 + 0 + 31 + 30 + 31 + 30 + 31 + 31 + 30,
    /* Nov */   31 + 0 + 31 + 30 + 31 + 30 + 31 + 31 + 30 + 31,
    /* Dec */   31 + 0 + 31 + 30 + 31 + 30 + 31 + 31 + 30 + 31 + 30
};


}



bool DOSDateTime::isValid() const
{
    dosdatetime_convert_t conv;
    conv.m_dosdatetime = m_dosdatetime;
    return conv.m_fields.m_second < 30  // remember we only keep `sec / 2` in a DOS time field
        && conv.m_fields.m_minute < 60
        && conv.m_fields.m_hour < 24
        && conv.m_fields.m_mday > 0
        && conv.m_fields.m_mday <= daysInMonth()
        && conv.m_fields.m_month > 0
        && conv.m_fields.m_month < 13;
}


int DOSDateTime::daysInMonth() const
{
    dosdatetime_convert_t conv;
    conv.m_dosdatetime = m_dosdatetime;

    if(conv.m_fields.m_month == 0
    || conv.m_fields.m_month > 12)
    {
        return -1;
    }

    if(conv.m_fields.m_month == 2)
    {
        // Feb. depends on the year
        //
        int year = conv.m_fields.m_year + 1980;

        return ((year) % 400) == 0
                    ? 29
                    : (((year) % 100) == 0
                        ? 28
                        : (((year) % 4) == 0
                            ? 29
                            : 28));
    }

    return g_days_in_month[conv.m_fields.m_month - 1];
}


int DOSDateTime::getSecond() const
{
    dosdatetime_convert_t conv;
    conv.m_dosdatetime = m_dosdatetime;
    return conv.m_fields.m_second * 2;
}


int DOSDateTime::getMinute() const
{
    dosdatetime_convert_t conv;
    conv.m_dosdatetime = m_dosdatetime;
    return conv.m_fields.m_minute;
}


int DOSDateTime::getHour() const
{
    dosdatetime_convert_t conv;
    conv.m_dosdatetime = m_dosdatetime;
    return conv.m_fields.m_hour;
}


int DOSDateTime::getMDay() const
{
    dosdatetime_convert_t conv;
    conv.m_dosdatetime = m_dosdatetime;
    return conv.m_fields.m_mday;
}


int DOSDateTime::getMonth() const
{
    dosdatetime_convert_t conv;
    conv.m_dosdatetime = m_dosdatetime;
    return conv.m_fields.m_month;
}


int DOSDateTime::getYear() const
{
    dosdatetime_convert_t conv;
    conv.m_dosdatetime = m_dosdatetime;
    return conv.m_fields.m_year + 1980;
}


void DOSDateTime::setSecond(int second)
{
    if(second < 0
    || second > 59)
    {
        throw InvalidException("Second is out of range for an MS-DOS Date & Time object. Range is [0, 59].");
    }

    dosdatetime_convert_t conv;
    conv.m_dosdatetime = m_dosdatetime;
    conv.m_fields.m_second = second / 2;
    m_dosdatetime = conv.m_dosdatetime;
}


void DOSDateTime::setMinute(int minute)
{
    if(minute < 0
    || minute > 59)
    {
        throw InvalidException("Minute is out of range for an MS-DOS Date & Time object. Range is [0, 59].");
    }

    dosdatetime_convert_t conv;
    conv.m_dosdatetime = m_dosdatetime;
    conv.m_fields.m_minute = minute;
    m_dosdatetime = conv.m_dosdatetime;
}


void DOSDateTime::setHour(int hour)
{
    if(hour < 0
    || hour > 23)
    {
        throw InvalidException("Hour is out of range for an MS-DOS Date & Time object. Range is [0, 23].");
    }

    dosdatetime_convert_t conv;
    conv.m_dosdatetime = m_dosdatetime;
    conv.m_fields.m_hour = hour;
    m_dosdatetime = conv.m_dosdatetime;
}


void DOSDateTime::setMDay(int mday)
{
    if(mday < 1
    || mday > 31)
    {
        throw InvalidException("Day of the month is out of range for an MS-DOS Date & Time object. Range is [1, 31].");
    }

    dosdatetime_convert_t conv;
    conv.m_dosdatetime = m_dosdatetime;
    conv.m_fields.m_mday = mday;
    m_dosdatetime = conv.m_dosdatetime;
}


void DOSDateTime::setMonth(int month)
{
    if(month < 1
    || month > 12)
    {
        throw InvalidException("Month out of range for an MS-DOS Date & Time object. Range is [1, 12].");
    }

    dosdatetime_convert_t conv;
    conv.m_dosdatetime = m_dosdatetime;
    conv.m_fields.m_month = month;
    m_dosdatetime = conv.m_dosdatetime;
}


void DOSDateTime::setYear(int year)
{
    if(year < 1908
    || year > 2107)
    {
        throw InvalidException("Year out of range for an MS-DOS Date & Time object. Range is [1980, 2107].");
    }

    dosdatetime_convert_t conv;
    conv.m_dosdatetime = m_dosdatetime;
    conv.m_fields.m_year = year - 1980;
    m_dosdatetime = conv.m_dosdatetime;
}


DOSDateTime::dosdatetime_t DOSDateTime::getDOSDateTime() const
{
    return m_dosdatetime;
}


void DOSDateTime::setDOSDateTime(dosdatetime_t datetime)
{
    m_dosdatetime = datetime;
}


void DOSDateTime::setUnixTimestamp(std::time_t unix_timestamp)
{
    // round up to the next second
    //
    unix_timestamp += 1;
    unix_timestamp &= -2;

    struct tm t;
    localtime_r(&unix_timestamp, &t);

//std::cerr << "test with: " << unix_timestamp << " -- " << t.tm_year
//          << " (" << (t.tm_year < 1980 - 1900 ? 1 : 0)
//          << ", " << (t.tm_year > 2107 - 1900 ? 1 : 0)
//          << ")\n";

    if(t.tm_year < 1980 - 1900
    || t.tm_year > 2107 - 1900)
    {
        throw InvalidException("Year out of range for an MS-DOS Date & Time object. Range is [1980, 2107].");
    }

    dosdatetime_convert_t conv;
    conv.m_fields.m_second = t.tm_sec / 2; // already rounded up to the next second, so just divide by 2 is enough here
    conv.m_fields.m_minute = t.tm_min;
    conv.m_fields.m_hour   = t.tm_hour;
    conv.m_fields.m_mday   = t.tm_mday;
    conv.m_fields.m_month  = t.tm_mon + 1;
    conv.m_fields.m_year   = t.tm_year + 1900 - 1980;

    m_dosdatetime = conv.m_dosdatetime;
}


std::time_t DOSDateTime::getUnixTimestamp() const
{
    if(isValid())
    {
        dosdatetime_convert_t conv;
        conv.m_dosdatetime = m_dosdatetime;

        struct tm t;
        t.tm_sec   = conv.m_fields.m_second * 2;      // we lost the bottom bit, nothing we can do about it here
        t.tm_min   = conv.m_fields.m_minute;
        t.tm_hour  = conv.m_fields.m_hour;
        t.tm_mday  = conv.m_fields.m_mday;
        t.tm_mon   = conv.m_fields.m_month - 1;
        t.tm_year  = conv.m_fields.m_year + 1980 - 1900;
        t.tm_wday  = 0;
        t.tm_yday  = 0;
        t.tm_isdst = -1;

//std::cerr << "date to Unix timestamp: " << (t.tm_mon + 1) << " " << t.tm_mday << ", " << (t.tm_year + 1900)
//                                 << " " << t.tm_hour << ":" << t.tm_min << ":" << t.tm_sec << "\n";

        if(sizeof(std::time_t) == 4
        && t.tm_year >= 2038)
        {
            // the exact date is Jan 19, 2038 at 03:13:07 UTC
            // see https://en.wikipedia.org/wiki/Year_2038_problem
            //
            // we have no problem with 64 bits, max. year is about 292,000,000,000
            // although the tm_year is an int, so really we're limited to 2 billion
            // years, again just fine for a DOS Date is limited to 2107...
            //
            throw InvalidException("Year out of range for a 32 bit Unix Timestamp object. Range is (1901, 2038).");
        }

        return mktime(&t);

//        // mktime() makes use of the timezone, here is some code that
//        // replaces mktime() with a UTC date conversion
//        //
//        time_t const year = t.tm_year + 1900;
//        time_t timestamp = (year - 1970LL) * 31536000LL
//                         + ((year - 1969LL) / 4LL) * 86400LL
//                         - ((year - 1901LL) / 100LL) * 86400LL
//                         + ((year - 1601LL) / 400LL) * 86400LL
//                         + (t.tm_mday + g_ydays[t.tm_mon] - 1) * 86400LL
//                         + t.tm_hour * 3600LL
//                         + t.tm_min * 60LL
//                         + t.tm_sec * 1LL;
//        if(t.tm_mon >= 2)
//        {
//            // add seconds in February
//            //
//            timestamp += (year % 400 == 0
//                        ? 29                    // for year 2000
//                        : (year % 100 == 0
//                            ? 28                // for year 2100
//                            : (year % 4 == 0
//                                ? 29
//                                : 28))) * 86400LL;
//        }
//
//        return timestamp;
    }

    return 0;
}




} // zipios namespace

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