// file      : butl/timestamp -*- C++ -*-
// copyright : Copyright (c) 2014-2015 Code Synthesis Ltd
// license   : MIT; see accompanying LICENSE file

#ifndef BUTL_TIMESTAMP
#define BUTL_TIMESTAMP

#include <chrono>
#include <iosfwd>

#include <butl/path>

namespace butl
{
  // On all three main platforms that we target (GNU/Linux, Windows (both
  // VC++ and GCC/MinGW64), and MacOS X) with recent C++ runtimes,
  // system_clock has nanoseconds resolution and counts from the UNIX
  // epoch. The latter is important since struct stat also returns times
  // based on UNIX epoch.
  //
  // The underlying type for nanoseconds duration is signed integer type
  // of at least 64 bits (currently int64_t). Because it is signed, we
  // will overflow in year 2262 but by then the underlying type will
  // most likely have changed to something larger than 64-bit.
  //
  // So to support other platforms that could possibly use a different
  // system_clock resolutions (e.g., microseconds), we actually not going
  // to assume anywhere (except perhaps timestamp.cxx) that we are dealing
  // with nanoseconds or the 64-bit underlying type.
  //
  using std::chrono::system_clock;

  // Note that uninitialized timestamp has the timestamp_nonexistent
  // value.
  //
  using timestamp = system_clock::time_point;
  using duration = system_clock::duration;

  // Generally-useful special values.
  //
  const timestamp timestamp_unknown {duration {-1}};
  const timestamp timestamp_nonexistent {duration {0}};

  // Human-readable representation. Note that these operators
  // may throw std::system_error.
  //
  std::ostream&
  operator<< (std::ostream&, const timestamp&);

  std::ostream&
  operator<< (std::ostream&, const duration&);
};

#endif // BUTL_TIMESTAMP