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// Copyright 2019 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#include "platform/api/time.h"
#include <ctime>
#include "gtest/gtest.h"
using std::chrono::seconds;
namespace openscreen {
#if __cplusplus < 202000L
// Before C++20, the standard does not guarantee that time_t is the number of
// seconds since the UNIX epoch. It also doesn't guarantee that one tick of
// time_t represents one second. However, this is so universally common, it's
// worth assuming the platform provides this.
TEST(TimeTest, TimeTMeetsTheCpp20Standard) {
// Use the functions the standard *does* provide for calendar time
// conversions to determine the value of time_t at the UNIX epoch.
std::tm epoch_tm;
epoch_tm.tm_sec = 0;
epoch_tm.tm_min = 0;
epoch_tm.tm_hour = 0;
epoch_tm.tm_mday = 1;
epoch_tm.tm_mon = 0;
epoch_tm.tm_year = 70; // 1970
epoch_tm.tm_isdst = 0;
// Note: std::mktime() assumes the translation is in the local time zone.
const std::time_t new_year_1970_in_local_tz = std::mktime(&epoch_tm);
// Purposely misinterpret |new_year_1970_in_local_tz| as UTC to provide
// information as to how to offset |epoch_tm| such that std::mktime() will
// be fooled into returning the value in terms of UTC.
std::tm* const wrong_tm = std::gmtime(&new_year_1970_in_local_tz);
epoch_tm.tm_sec += epoch_tm.tm_sec - wrong_tm->tm_sec;
epoch_tm.tm_min += epoch_tm.tm_min - wrong_tm->tm_min;
epoch_tm.tm_hour += epoch_tm.tm_hour - wrong_tm->tm_hour;
epoch_tm.tm_mday += epoch_tm.tm_mday - wrong_tm->tm_mday;
epoch_tm.tm_mon += epoch_tm.tm_mon - wrong_tm->tm_mon;
epoch_tm.tm_year += epoch_tm.tm_year - wrong_tm->tm_year;
const std::time_t epoch = std::mktime(&epoch_tm);
EXPECT_EQ(seconds(0), seconds(epoch));
++epoch_tm.tm_sec;
const std::time_t epoch_plus_one_second = std::mktime(&epoch_tm);
EXPECT_EQ(seconds(1), seconds(epoch_plus_one_second));
}
#endif
} // namespace openscreen
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