Date.cc

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#include "Date.hh"
#include <array>
#include <concepts>
#include <iomanip>
#include <sstream>
#include <string_view>
 
namespace openmsx::Date {
 
static constexpr std::array<std::string_view, 7> days = {
        "Sun", "Mon", "Tue", "Wed", "Thu", "Fri", "Sat"
};
 
static constexpr std::array<std::string_view, 12> months = {
        "Jan", "Feb", "Mar", "Apr", "May", "Jun",
        "Jul", "Aug", "Sep", "Oct", "Nov", "Dec"
};
 
template<bool FIRST, unsigned MUL>
[[nodiscard]] static constexpr bool parseDigit(unsigned c, std::integral auto& t)
{
        c -= '0';
        if (c > 9) return false;
        if constexpr (FIRST) {
                t = c * MUL;
        } else {
                t += c * MUL;
        }
        return true;
}
 
time_t fromString(std::span<const char, 24> s)
{
        struct tm tm{};
 
        // skip day
 
        // space
        if (s[3] != ' ') return INVALID_TIME_T;
 
        // Parse month
        switch (s[4]) {
        case 'J': // Jan Jun Jul
                switch (s[5]) {
                case 'a': // Jan
                        if (s[6] != 'n') return INVALID_TIME_T;
                        tm.tm_mon = 0; break;
                case 'u': // Jun Jul
                        switch (s[6]) {
                        case 'n': tm.tm_mon = 5; break;
                        case 'l': tm.tm_mon = 6; break;
                        default: return INVALID_TIME_T;
                        }
                        break;
                default: return INVALID_TIME_T;
                }
                break;
        case 'F': // Feb
                if (s[5] != 'e') return INVALID_TIME_T;
                if (s[6] != 'b') return INVALID_TIME_T;
                tm.tm_mon = 1;
                break;
        case 'M': // Mar May
                if (s[5] != 'a') return INVALID_TIME_T;
                switch (s[6]) {
                case 'r': tm.tm_mon = 2; break;
                case 'y': tm.tm_mon = 4; break;
                default: return INVALID_TIME_T;
                }
                break;
        case 'A': // Apr Aug
                switch (s[5]) {
                case 'p': // Apr
                        if (s[6] != 'r') return INVALID_TIME_T;
                        tm.tm_mon = 3; break;
                case 'u': // Aug
                        if (s[6] != 'g') return INVALID_TIME_T;
                        tm.tm_mon = 7; break;
                default: return INVALID_TIME_T;
                }
                break;
        case 'S': // Sep
                if (s[5] != 'e') return INVALID_TIME_T;
                if (s[6] != 'p') return INVALID_TIME_T;
                tm.tm_mon = 8;
                break;
        case 'O': // Oct
                if (s[5] != 'c') return INVALID_TIME_T;
                if (s[6] != 't') return INVALID_TIME_T;
                tm.tm_mon = 9;
                break;
        case 'N': // Nov
                if (s[5] != 'o') return INVALID_TIME_T;
                if (s[6] != 'v') return INVALID_TIME_T;
                tm.tm_mon = 10;
                break;
        case 'D': // Dec
                if (s[5] != 'e') return INVALID_TIME_T;
                if (s[6] != 'c') return INVALID_TIME_T;
                tm.tm_mon = 11;
                break;
        default: return INVALID_TIME_T;
        }
 
        // space
        if (s[7] != ' ') return INVALID_TIME_T;
 
        // parse mday
        if (!parseDigit<true, 10>(s[8], tm.tm_mday)) return INVALID_TIME_T;
        if (!parseDigit<false, 1>(s[9], tm.tm_mday)) return INVALID_TIME_T;
        if ((tm.tm_mday < 1) || (31 < tm.tm_mday))   return INVALID_TIME_T;
 
        // space
        if (s[10] != ' ') return INVALID_TIME_T;
 
        // parse hour
        if (!parseDigit<true, 10>(s[11], tm.tm_hour)) return INVALID_TIME_T;
        if (!parseDigit<false, 1>(s[12], tm.tm_hour)) return INVALID_TIME_T;
        if ((tm.tm_hour < 0) || (23 < tm.tm_hour))   return INVALID_TIME_T;
 
        // colon
        if (s[13] != ':') return INVALID_TIME_T;
 
        // parse minute
        if (!parseDigit<true, 10>(s[14], tm.tm_min)) return INVALID_TIME_T;
        if (!parseDigit<false, 1>(s[15], tm.tm_min)) return INVALID_TIME_T;
        if ((tm.tm_min < 0) || (59 < tm.tm_min))    return INVALID_TIME_T;
 
        // colon
        if (s[16] != ':') return INVALID_TIME_T;
 
        // parse second
        if (!parseDigit<true, 10>(s[17], tm.tm_sec)) return INVALID_TIME_T;
        if (!parseDigit<false, 1>(s[18], tm.tm_sec)) return INVALID_TIME_T;
        if ((tm.tm_sec < 0) || (59 < tm.tm_sec))    return INVALID_TIME_T;
 
        // space
        if (s[19] != ' ') return INVALID_TIME_T;
 
        // parse year
        if (!parseDigit<true, 1000>(s[20], tm.tm_year)) return INVALID_TIME_T;
        if (!parseDigit<false, 100>(s[21], tm.tm_year)) return INVALID_TIME_T;
        if (!parseDigit<false,  10>(s[22], tm.tm_year)) return INVALID_TIME_T;
        if (!parseDigit<false,   1>(s[23], tm.tm_year)) return INVALID_TIME_T;
        tm.tm_year -= 1900;
        if (tm.tm_year < 0) return INVALID_TIME_T;
 
        tm.tm_isdst = -1;
        return mktime(&tm);
}
 
std::string toString(time_t time)
{
        if (time < 0) time = 0;
        struct tm* tm = localtime(&time);
        std::ostringstream sstr;
        sstr << std::setfill('0')
             << days  [tm->tm_wday] << ' '
             << months[tm->tm_mon]  << ' '
             << std::setw(2) << tm->tm_mday << ' '
             << std::setw(2) << tm->tm_hour << ':'
             << std::setw(2) << tm->tm_min  << ':'
             << std::setw(2) << tm->tm_sec  << ' '
             << std::setw(4) << (tm->tm_year + 1900);
        return sstr.str();
}
 
} // namespace openmsx::Date