// 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 "util/alarm.h"

#include <algorithm>
#include <chrono>

#include "gtest/gtest.h"
#include "platform/test/fake_clock.h"
#include "platform/test/fake_task_runner.h"
#include "util/chrono_helpers.h"

namespace openscreen {
namespace {

class AlarmTest : public testing::Test {
 public:
  FakeClock* clock() { return &clock_; }
  FakeTaskRunner* task_runner() { return &task_runner_; }
  Alarm* alarm() { return &alarm_; }

 private:
  FakeClock clock_{Clock::now()};
  FakeTaskRunner task_runner_{&clock_};
  Alarm alarm_{&FakeClock::now, &task_runner_};
};

TEST_F(AlarmTest, RunsTaskAsClockAdvances) {
  constexpr Clock::duration kDelay = milliseconds(20);

  const Clock::time_point alarm_time = FakeClock::now() + kDelay;
  Clock::time_point actual_run_time{};
  alarm()->Schedule([&]() { actual_run_time = FakeClock::now(); }, alarm_time);
  // Confirm the lambda did not run immediately.
  ASSERT_EQ(Clock::time_point{}, actual_run_time);

  // Confirm the lambda does not run until the necessary delay has elapsed.
  clock()->Advance(kDelay / 2);
  ASSERT_EQ(Clock::time_point{}, actual_run_time);

  // Confirm the lambda is called when the necessary delay has elapsed.
  clock()->Advance(kDelay / 2);
  ASSERT_EQ(alarm_time, actual_run_time);

  // Confirm the lambda is only run once.
  clock()->Advance(kDelay * 100);
  ASSERT_EQ(alarm_time, actual_run_time);
}

TEST_F(AlarmTest, RunsTaskImmediately) {
  const Clock::time_point expected_run_time = FakeClock::now();
  Clock::time_point actual_run_time{};
  alarm()->Schedule([&]() { actual_run_time = FakeClock::now(); },
                    Alarm::kImmediately);
  // Confirm the lambda did not run yet, since it should run asynchronously, in
  // a separate TaskRunner task.
  ASSERT_EQ(Clock::time_point{}, actual_run_time);

  // Confirm the lambda runs without the clock having to tick forward.
  task_runner()->RunTasksUntilIdle();
  ASSERT_EQ(expected_run_time, actual_run_time);

  // Confirm the lambda is only run once.
  clock()->Advance(seconds(2));
  ASSERT_EQ(expected_run_time, actual_run_time);
}

TEST_F(AlarmTest, CancelsTaskWhenGoingOutOfScope) {
  constexpr Clock::duration kDelay = milliseconds(20);
  constexpr Clock::time_point kNever{};

  Clock::time_point actual_run_time{};
  {
    Alarm scoped_alarm(&FakeClock::now, task_runner());
    const Clock::time_point alarm_time = FakeClock::now() + kDelay;
    scoped_alarm.Schedule([&]() { actual_run_time = FakeClock::now(); },
                          alarm_time);
    // |scoped_alarm| is destroyed.
  }

  // Confirm the lambda has never and will never run.
  ASSERT_EQ(kNever, actual_run_time);
  clock()->Advance(kDelay * 100);
  ASSERT_EQ(kNever, actual_run_time);
}

TEST_F(AlarmTest, Cancels) {
  constexpr Clock::duration kDelay = milliseconds(20);

  const Clock::time_point alarm_time = FakeClock::now() + kDelay;
  Clock::time_point actual_run_time{};
  alarm()->Schedule([&]() { actual_run_time = FakeClock::now(); }, alarm_time);

  // Advance the clock for half the delay, and confirm the lambda has not run
  // yet.
  clock()->Advance(kDelay / 2);
  ASSERT_EQ(Clock::time_point{}, actual_run_time);

  // Cancel and then advance the clock well past the delay, and confirm the
  // lambda has never run.
  alarm()->Cancel();
  clock()->Advance(kDelay * 100);
  ASSERT_EQ(Clock::time_point{}, actual_run_time);
}

TEST_F(AlarmTest, CancelsAndRearms) {
  constexpr Clock::duration kShorterDelay = milliseconds(10);
  constexpr Clock::duration kLongerDelay = milliseconds(100);

  // Run the test twice: Once when scheduling first with a long delay, then a
  // shorter delay; and once when scheduling first with a short delay, then a
  // longer delay. This is to test Alarm's internal scheduling/firing logic.
  for (int do_longer_then_shorter = 0; do_longer_then_shorter <= 1;
       ++do_longer_then_shorter) {
    const auto delay1 = do_longer_then_shorter ? kLongerDelay : kShorterDelay;
    const auto delay2 = do_longer_then_shorter ? kShorterDelay : kLongerDelay;

    int count1 = 0;
    alarm()->Schedule([&]() { ++count1; }, FakeClock::now() + delay1);

    // Advance the clock for half of |delay1|, and confirm the lambda that
    // increments the variable does not run.
    ASSERT_EQ(0, count1);
    clock()->Advance(delay1 / 2);
    ASSERT_EQ(0, count1);

    // Schedule a different lambda, that increments a different variable, to run
    // after |delay2|.
    int count2 = 0;
    alarm()->Schedule([&]() { ++count2; }, FakeClock::now() + delay2);

    // Confirm the second scheduling will fire at the right moment.
    clock()->Advance(delay2 / 2);
    ASSERT_EQ(0, count2);
    clock()->Advance(delay2 / 2);
    ASSERT_EQ(1, count2);

    // Confirm the second scheduling never fires a second time, and also that
    // the first one doesn't fire.
    clock()->Advance(std::max(delay1, delay2) * 100);
    ASSERT_EQ(0, count1);
    ASSERT_EQ(1, count2);
  }
}

}  // namespace
}  // namespace openscreen