// Copyright (c) 2011-present, Facebook, Inc.  All rights reserved.
//  This source code is licensed under both the GPLv2 (found in the
//  COPYING file in the root directory) and Apache 2.0 License
//  (found in the LICENSE.Apache file in the root directory).

#pragma once

#include <atomic>
#include <limits>

#include "port/port.h"
#include "rocksdb/system_clock.h"
#include "test_util/mock_time_env.h"
#include "test_util/sync_point.h"
#include "util/random.h"

namespace ROCKSDB_NAMESPACE {

// NOTE: SpecialEnv offers most of this functionality, along with hooks
// for safe DB behavior under a mock time environment, so should be used
// instead of MockSystemClock for DB tests.
class MockSystemClock : public SystemClockWrapper {
 public:
  explicit MockSystemClock(const std::shared_ptr<SystemClock>& base)
      : SystemClockWrapper(base) {}

  static const char* kClassName() { return "MockSystemClock"; }
  const char* Name() const override { return kClassName(); }
  Status GetCurrentTime(int64_t* time_sec) override {
    assert(time_sec != nullptr);
    *time_sec = static_cast<int64_t>(current_time_us_ / kMicrosInSecond);
    return Status::OK();
  }

  virtual uint64_t NowSeconds() { return current_time_us_ / kMicrosInSecond; }

  uint64_t NowMicros() override { return current_time_us_; }

  uint64_t NowNanos() override {
    assert(current_time_us_ <= std::numeric_limits<uint64_t>::max() / 1000);
    return current_time_us_ * 1000;
  }

  uint64_t RealNowMicros() { return target_->NowMicros(); }

  void SetCurrentTime(uint64_t time_sec) {
    assert(time_sec < std::numeric_limits<uint64_t>::max() / kMicrosInSecond);
    assert(time_sec * kMicrosInSecond >= current_time_us_);
    current_time_us_ = time_sec * kMicrosInSecond;
  }

  // It's a fake sleep that just updates the Env current time, which is similar
  // to `NoSleepEnv.SleepForMicroseconds()` and
  // `SpecialEnv.MockSleepForMicroseconds()`.
  // It's also similar to `set_current_time()`, which takes an absolute time in
  // seconds, vs. this one takes the sleep in microseconds.
  // Note: Not thread safe.
  void SleepForMicroseconds(int micros) override {
    assert(micros >= 0);
    assert(current_time_us_ + static_cast<uint64_t>(micros) >=
           current_time_us_);
    current_time_us_.fetch_add(micros);
  }

  void MockSleepForSeconds(int seconds) {
    assert(seconds >= 0);
    uint64_t micros = static_cast<uint64_t>(seconds) * kMicrosInSecond;
    assert(current_time_us_ + micros >= current_time_us_);
    current_time_us_.fetch_add(micros);
  }

  bool TimedWait(port::CondVar* cv,
                 std::chrono::microseconds deadline) override {
    uint64_t now_micros = NowMicros();
    uint64_t deadline_micros = static_cast<uint64_t>(deadline.count());
    uint64_t delay_micros;
    if (deadline_micros > now_micros) {
      delay_micros = deadline_micros - now_micros;
    } else {
      delay_micros = 0;
    }
    // To prevent slowdown, this `TimedWait()` is completely synthetic. First,
    // it yields to coerce other threads to run while the lock is released.
    // Second, it randomly selects between mocking an immediate wakeup and a
    // timeout.
    cv->GetMutex()->Unlock();
    std::this_thread::yield();
    bool mock_timeout = Random::GetTLSInstance()->OneIn(2);
    if (mock_timeout) {
      TEST_SYNC_POINT("MockSystemClock::TimedWait:UnlockedPreSleep");
      current_time_us_.fetch_add(delay_micros);
      TEST_SYNC_POINT("MockSystemClock::TimedWait:UnlockedPostSleep1");
      TEST_SYNC_POINT("MockSystemClock::TimedWait:UnlockedPostSleep2");
    }
    cv->GetMutex()->Lock();
    return mock_timeout;
  }

  // TODO: this is a workaround for the different behavior on different platform
  // for timedwait timeout. Ideally timedwait API should be moved to env.
  // details: PR #7101.
  void InstallTimedWaitFixCallback();

 private:
  std::atomic<uint64_t> current_time_us_{0};
  static constexpr uint64_t kMicrosInSecond = 1000U * 1000U;
};

}  // namespace ROCKSDB_NAMESPACE