////////////////////////////////////////////////////////////////////////////////
/// DISCLAIMER
///
/// Copyright 2014-2016 ArangoDB GmbH, Cologne, Germany
/// Copyright 2004-2014 triAGENS GmbH, Cologne, Germany
///
/// Licensed under the Apache License, Version 2.0 (the "License");
/// you may not use this file except in compliance with the License.
/// You may obtain a copy of the License at
///
///     http://www.apache.org/licenses/LICENSE-2.0
///
/// Unless required by applicable law or agreed to in writing, software
/// distributed under the License is distributed on an "AS IS" BASIS,
/// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
/// See the License for the specific language governing permissions and
/// limitations under the License.
///
/// Copyright holder is ArangoDB GmbH, Cologne, Germany
///
/// @author Max Neunhoeffer
////////////////////////////////////////////////////////////////////////////////

#include "Basics/HybridLogicalClock.h"

namespace {
template <typename DurationT, typename ReprT = typename DurationT::rep>
constexpr DurationT maxDuration() noexcept {
  return DurationT{(std::numeric_limits<ReprT>::max)()};
}

template <typename DurationT>
constexpr DurationT absDuration(const DurationT d) noexcept {
  return DurationT{(d.count() < 0) ? -d.count() : d.count()};
}

template <typename SrcTimePointT, typename DstTimePointT, typename SrcDurationT = typename SrcTimePointT::duration,
          typename DstDurationT = typename DstTimePointT::duration,
          typename SrcClockT = typename SrcTimePointT::clock, typename DstClockT = typename DstTimePointT::clock>
DstDurationT clockOffset(const SrcDurationT tolerance = std::chrono::duration_cast<SrcDurationT>(
                             std::chrono::nanoseconds{300}),
                         const int limit = 10000) {
  if (std::is_same<SrcClockT, DstClockT>::value) {
    return SrcClockT::from_time_t(0).time_since_epoch();
  }

  auto itercnt = 0;
  auto src_now = SrcTimePointT{};
  auto dst_now = DstTimePointT{};
  auto epsilon = maxDuration<SrcDurationT>();
  do {
    const auto src_before = SrcClockT::now();
    const auto dst_between = DstClockT::now();
    const auto src_after = SrcClockT::now();
    const auto src_diff = src_after - src_before;
    const auto delta = absDuration(src_diff);
    if (delta < epsilon) {
      src_now = src_before + src_diff / 2;
      dst_now = dst_between;
      epsilon = delta;
    }
    if (++itercnt >= limit) {
      break;
    }
  } while (epsilon > tolerance);

  auto diff1970 = SrcClockT::from_time_t(0) - src_now;

  return (dst_now + diff1970).time_since_epoch();
}
}  // namespace

char arangodb::basics::HybridLogicalClock::encodeTable[65] =
    "-_ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789";

signed char arangodb::basics::HybridLogicalClock::decodeTable[256] = {
    -1, -1, -1, -1, -1, -1, -1, -1,
    -1, -1, -1, -1, -1, -1, -1, -1,  //   0 - 15
    -1, -1, -1, -1, -1, -1, -1, -1,
    -1, -1, -1, -1, -1, -1, -1, -1,  //  16 - 31
    -1, -1, -1, -1, -1, -1, -1, -1,
    -1, -1, -1, -1, -1, 0,  -1, -1,  //  32 - 47
    54, 55, 56, 57, 58, 59, 60, 61,
    62, 63, -1, -1, -1, -1, -1, -1,  //  48 - 63
    -1, 2,  3,  4,  5,  6,  7,  8,
    9,  10, 11, 12, 13, 14, 15, 16,  //  64 - 79
    17, 18, 19, 20, 21, 22, 23, 24,
    25, 26, 27, -1, -1, -1, -1, 1,  //  80 - 95
    -1, 28, 29, 30, 31, 32, 33, 34,
    35, 36, 37, 38, 39, 40, 41, 42,  //  96 - 111
    43, 44, 45, 46, 47, 48, 49, 50,
    51, 52, 53, -1, -1, -1, -1, -1,  // 112 - 127
    -1, -1, -1, -1, -1, -1, -1, -1,
    -1, -1, -1, -1, -1, -1, -1, -1,  // 128 - 143
    -1, -1, -1, -1, -1, -1, -1, -1,
    -1, -1, -1, -1, -1, -1, -1, -1,  // 144 - 159
    -1, -1, -1, -1, -1, -1, -1, -1,
    -1, -1, -1, -1, -1, -1, -1, -1,  // 160 - 175
    -1, -1, -1, -1, -1, -1, -1, -1,
    -1, -1, -1, -1, -1, -1, -1, -1,  // 176 - 191
    -1, -1, -1, -1, -1, -1, -1, -1,
    -1, -1, -1, -1, -1, -1, -1, -1,  // 192 - 207
    -1, -1, -1, -1, -1, -1, -1, -1,
    -1, -1, -1, -1, -1, -1, -1, -1,  // 208 - 223
    -1, -1, -1, -1, -1, -1, -1, -1,
    -1, -1, -1, -1, -1, -1, -1, -1,  // 224 - 239
    -1, -1, -1, -1, -1, -1, -1, -1,
    -1, -1, -1, -1, -1, -1, -1, -1};  // 240 - 255

uint64_t arangodb::basics::HybridLogicalClock::computeOffset1970() {
  auto diff =
      clockOffset<std::chrono::system_clock::time_point, HybridLogicalClock::ClockT::time_point>();

  return std::chrono::duration_cast<std::chrono::milliseconds>(diff).count();
}