//    OpenVPN -- An application to securely tunnel IP networks
//               over a single port, with support for SSL/TLS-based
//               session authentication and key exchange,
//               packet encryption, packet authentication, and
//               packet compression.
//
//    Copyright (C) 2012-2020 OpenVPN Inc.
//
//    This program is free software: you can redistribute it and/or modify
//    it under the terms of the GNU Affero General Public License Version 3
//    as published by the Free Software Foundation.
//
//    This program 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 Affero General Public License for more details.
//
//    You should have received a copy of the GNU Affero General Public License
//    along with this program in the COPYING file.
//    If not, see <http://www.gnu.org/licenses/>.

// These are our fundamental Time and Time Duration classes.
// We normally deal with time in units of 1/1024 of a second.
// This allows us to use 32-bit values to represent most time
// and time duration values, but still gives us reasonable
// accuracy.  Using units of 1/1024 of a second vs. straight
// milliseconds gives us an advantage of not needing to do
// very much integer multiplication and division which can
// help us on platforms such as ARM that lack integer division
// instructions.  Note that the data type used to store the time
// is an oulong, so it will automatically expand to 64 bits on
// 64-bit machines (see olong.hpp).  Using a 32-bit
// data type for time durations is normally fine for clients,
// but imposes a wraparound limit of ~ 48 days.  Servers
// should always use a 64-bit data type to avoid this
// limitation.

// This code was originally designed to be efficient on 32-bit
// processors.  On 64-bit processors, define OPENVPN_TIME_NO_BASE
// to optimize out the base_ variable.  This also has the benefit
// of allowing Time to represent any arbitrary time_t value.

#ifndef OPENVPN_TIME_TIME_H
#define OPENVPN_TIME_TIME_H

#include <limits>
#include <cstdint> // for std::uint32_t, uint64_t

#include <openvpn/common/platform.hpp>
#include <openvpn/common/exception.hpp>
#include <openvpn/common/olong.hpp>
#include <openvpn/common/to_string.hpp>

#ifdef OPENVPN_PLATFORM_WIN
#include <time.h>     // for ::time() on Windows
#include <windows.h>  // for GetTickCount
#else
#include <sys/time.h> // for ::time() and ::gettimeofday()
#endif

namespace openvpn {
  OPENVPN_SIMPLE_EXCEPTION(get_time_error);

  template <typename T>
  class TimeType
  {
  public:
    enum { prec=1024 };
    typedef ::time_t base_type;
    typedef T type;

    class Duration
    {
      friend class TimeType;

    public:
      static Duration seconds(const T v) { return Duration(v * prec); }
      static Duration binary_ms(const T v) { return Duration(v); }
      static Duration infinite() { return Duration(std::numeric_limits<T>::max()); }

      static Duration milliseconds(const T v)
      {
	// NOTE: assumes that prec == 1024
	// Also note that this might wrap if v is larger than 1/3 of max size of T
	return Duration(v + (v * T(3) / T(128)));
      }

      Duration() noexcept : duration_(T(0)) {}

      bool defined() const { return duration_ != T(0); }
      bool operator!() const { return duration_ == T(0); }
      bool is_infinite() const { return duration_ == std::numeric_limits<T>::max(); }
      bool enabled() const { return defined() && !is_infinite(); }
      void set_infinite() { duration_ = std::numeric_limits<T>::max(); }
      void set_zero() { duration_ = T(0); }

      Duration operator+(const Duration& d) const
      {
	if (is_infinite() || d.is_infinite())
	  return infinite();
	else
	  return Duration(duration_ + d.duration_);
      }

      Duration operator+(const int delta) const
      {
	T duration = duration_;
	if (delta >= 0)
	  duration += delta;
	else
	  {
	    const unsigned int ndelta = -delta;
	    if (duration_ >= ndelta)
	      duration -= ndelta;
	    else
	      duration = 0;
	  }
	return Duration(duration);
      }

      Duration operator*(const unsigned int mult) const
      {
	return Duration(duration_ * mult);
      }

      Duration& operator+=(const Duration& d)
      {
	if (is_infinite() || d.is_infinite())
	  set_infinite();
	else
	  duration_ += d.duration_;
	return *this;
      }

      void min(const Duration& d)
      {
	if (d.duration_ < duration_)
	  duration_ = d.duration_;
      }

      void max(const Duration& d)
      {
	if (d.duration_ > duration_)
	  duration_ = d.duration_;
      }

      Duration operator-(const Duration& d) const
      {
	if (d.duration_ >= duration_)
	  return Duration(0);
	else if (is_infinite())
	  return Duration::infinite();
	else
	  return Duration(duration_ - d.duration_);
      }

      Duration& operator-=(const Duration& d)
      {
	if (d.duration_ >= duration_)
	  set_zero();
	else if (!is_infinite())
	  duration_ -= d.duration_;
	return *this;
      }

      T to_seconds() const { return duration_ / prec; }
      T to_binary_ms() const { return duration_; }

      T to_milliseconds() const
      {
	// NOTE: assumes that prec == 1024
	// Also note that this might wrap if duration_ is larger than 1/3 of max size of T
	return duration_ - (duration_ * T(3) / T(128));
      }

      double to_double() const
      {
	return double(duration_) / double(prec);
      }

      T raw() const { return duration_; }

#     define OPENVPN_DURATION_REL(OP) bool operator OP(const Duration& d) const { return duration_ OP d.duration_; }
      OPENVPN_DURATION_REL(==)
      OPENVPN_DURATION_REL(!=)
      OPENVPN_DURATION_REL(>)
      OPENVPN_DURATION_REL(<)
      OPENVPN_DURATION_REL(>=)
      OPENVPN_DURATION_REL(<=)
#     undef OPENVPN_DURATION_REL

    private:
      explicit Duration(const T duration) : duration_(duration) {}

      T duration_;
    };

    TimeType() noexcept : time_(T(0)) {}

    static TimeType zero() { return TimeType(T(0)); }
    static TimeType infinite() { return TimeType(std::numeric_limits<T>::max()); }

    static TimeType from_seconds_since_epoch(const time_t t)
    {
      if (t <= base_)
	return TimeType(T(1));
      else
	return TimeType(T((t - base_) * prec));
    }

    bool is_infinite() const { return time_ == std::numeric_limits<T>::max(); }

    void reset() { time_ = 0; }
    void set_infinite() { time_ = std::numeric_limits<T>::max(); }

    bool defined() const { return time_ != 0; }
    bool operator!() const { return time_ == 0; }

    base_type seconds_since_epoch() const { return base_ + time_ / prec; }
    T fractional_binary_ms() const { return time_ % prec; }

    static TimeType now() { return TimeType(now_()); }

    void update() { time_ = now_(); }

    TimeType operator+(const Duration& d) const
    {
      if (is_infinite() || d.is_infinite())
	return infinite();
      else
	return TimeType(time_ + d.duration_);
    }

    TimeType& operator+=(const Duration& d)
    {
      if (is_infinite() || d.is_infinite())
	set_infinite();
      else
	time_ += d.duration_;
      return *this;
    }

    Duration operator-(const TimeType& t) const
    {
      if (t.time_ >= time_)
	return Duration(0);
      else if (is_infinite())
	return Duration::infinite();
      else
	return Duration(time_ - t.time_);
    }

    void min(const TimeType& t)
    {
      if (t.time_ < time_)
	time_ = t.time_;
    }

    void max(const TimeType& t)
    {
      if (t.time_ > time_)
	time_ = t.time_;
    }

    long delta_prec(const TimeType& t) const
    {
      return long(time_) - long(t.time_);
    }

    long delta(const TimeType& t) const
    {
      return delta_prec(t) / long(prec);
    }

    double delta_float(const TimeType& t) const
    {
      return (double(time_) - double(t.time_)) / double(prec);
    }

    // Return a human-readable number of seconds that *this is ahead of t.
    // t is usually now().
    std::string delta_str(const TimeType& t) const
    {
      if (!defined())
	return "UNDEF-TIME";
      if (is_infinite())
	return "INF";
      const double df = delta_float(t);
      std::string ret;
      if (df >= 0.0)
	ret += '+';
      ret += openvpn::to_string(df);
      return ret;
    }

#   define OPENVPN_TIME_REL(OP) bool operator OP(const TimeType& t) const { return time_ OP t.time_; }
    OPENVPN_TIME_REL(==)
    OPENVPN_TIME_REL(!=)
    OPENVPN_TIME_REL(>)
    OPENVPN_TIME_REL(<)
    OPENVPN_TIME_REL(>=)
    OPENVPN_TIME_REL(<=)
#   undef OPENVPN_TIME_REL

    T raw() const { return time_; }

    static void reset_base_conditional()
    {
      // on 32-bit systems, reset time base after 30 days
      if (sizeof(T) == 4)
	{
	  const base_type newbase = ::time(0);
	  if (newbase - base_ >= (60*60*24*30))
	    reset_base();
	}
    }

    static void reset_base()
    {
#ifdef OPENVPN_TIME_NO_BASE
      static_assert(sizeof(base_type) >= 8, "OPENVPN_TIME_NO_BASE requires time_t to be 64 bits");
#else
      base_ = ::time(0);
#ifdef OPENVPN_PLATFORM_WIN
#if (_WIN32_WINNT >= 0x0600)
      win_recalibrate((DWORD)::GetTickCount64());
#else
      win_recalibrate(::GetTickCount());
#endif
#endif
#endif
    }

    // number of tenths of a microsecond since January 1, 1601.
    static uint64_t win_time()
    {
      // NOTE: assumes that prec == 1024
      return ((11644473600ULL * uint64_t(prec)) + (uint64_t(base_) * uint64_t(prec)) + uint64_t(now_())) * 78125ULL / 8ULL;
    }

  private:
    explicit TimeType(const T time) : time_(time) {}

#ifdef OPENVPN_PLATFORM_WIN

    static void win_recalibrate(const DWORD gtc)
    {
      gtc_last = gtc;
      gtc_base = ::time(0) - gtc_last/1000;
    }

    static T now_()
    {
#if (_WIN32_WINNT >= 0x0600)
      const DWORD gtc = (DWORD)::GetTickCount64();
#else
      const DWORD gtc = ::GetTickCount();
#endif
      if (gtc < gtc_last)
	win_recalibrate(gtc);
      const time_t sec = gtc_base + gtc / 1000;
      const unsigned int msec = gtc % 1000;
      return T((sec - base_) * prec + msec * prec / 1000);
    }

    static DWORD gtc_last;
    static time_t gtc_base;

#else

    static T now_()
    {
      ::timeval tv;
      if (::gettimeofday(&tv, nullptr) != 0)
	throw get_time_error();
      return T((tv.tv_sec - base_) * prec + tv.tv_usec * prec / 1000000);
    }

#endif

#ifdef OPENVPN_TIME_NO_BASE
    static constexpr base_type base_ = 0;
#else
    static base_type base_;
#endif

    T time_;
  };

#ifdef OPENVPN_PLATFORM_WIN
  template <typename T> DWORD TimeType<T>::gtc_last;
  template <typename T> time_t TimeType<T>::gtc_base;
#endif

#ifndef OPENVPN_TIME_NO_BASE
  template <typename T> typename TimeType<T>::base_type TimeType<T>::base_;
#endif

  typedef TimeType<oulong> Time;

  typedef Time* TimePtr;

} // namespace openvpn

#endif // OPENVPN_TIME_TIME_H