//
//  performance_test.h
//
//  Created by Sam Jaffe on 11/4/23.
//  Copyright © 2020 Sam Jaffe. All rights reserved.
//

#pragma once
#define CONCAT2(A, B) A##B
#define CONCAT(A, B) CONCAT2(A, B)

#include <chrono>

#include <testing/xcode_gtest_helper.h>

#if __cplusplus >= 202002L
#elif defined(__has_include) && __has_include(<date/date.h>)
#include <date/date.h>
using date::operator<<;
#else
namespace std::chrono {
template <typename Rep, typename Period>
ostream &operator<<(ostream &os, duration<Rep, Period> const & dur) {
  os << dur.count();
  if (Period::den == 1) {
    switch (Period::num) {
    case 1: return os << 's';
    case 60: return os << 'm';
    case 3600: return os << 'h';
    case 86400: return os << 'd';
    }
  } else if (Period::num == 1) {
    switch (Period::den) {
    case 1000: return os << "ms";
    case 1000'000: return os << "\u00B5s";
    case 1000'000'000: return os << "ns";
    }
  }
  return os << Period::num << '/' << Period::den << 's';
}
}
#endif

#define PERF_TEST_CLASS(name) CONCAT(PerfTest, name)

/**
 * Example code using TEST_PERF:
 *
 * TEST_PERF(MyClassTest, Initialization, 50ms) {
 *   ... setup input variables ...
 *   MyClass object(...);
 *   (void) object;
 * }
 *
 * void ComplexTest::SetUp() {
 *   ... setup input variables as above to keep out of perf test ...
 *   object = MyClass(...);
 * }
 *
 * TEST_PERF_F(ComplexTest, ExpensiveFunction, 100ms) {
 *   this->object.ExpensiveFunction();
 * }
 */
#define TEST_PERF(test_suite_name, test_name, limit)                        \
    PERFORMANCE_FIXTURE_IMPL(test_suite_name, test_name, testing::Test, limit)

#define TEST_PERF_F(test_fixture, test_name, limit)          \
    PERFORMANCE_FIXTURE_IMPL(test_suite_name, test_name, test_suite_name, limit)

#define PERFORMANCE_TEST_CLASS(suite, case) CONCAT(suite, CONCAT(_, case))
#define PERFORMANCE_FIXTURE_IMPL(suite, case, parent, limit) \
    class PERFORMANCE_TEST_CLASS(suite, case) : public parent { \
    protected: \
      void TestImpl(); \
    }; \
    TEST_F(PERFORMANCE_TEST_CLASS(suite, case), Performance) { \
      EXPECT_PERFORMANCE(TestImpl(), limit); \
    } \
    void PERFORMANCE_TEST_CLASS(suite, case)::TestImpl()

/**
 * Example code using EXPECT_PERFORMANCE:
 * using std::literals::chrono_literals::operator""ms;
 *
 * TEST(MyClassPerfTest, Initialization) {
 *   EXPECT_PERFORMANCE(MyClass(...), testing::Le(50ms));
 * }
 *
 * TEST(MyClassPerfTest, ExpensiveFunction) {
 *   MyClass object(...);
 *   EXPECT_PERFORMANCE(object.ExpensiveFunction(), testing::Le(100ms));
 * }
 */
#define EXPECT_PERFORMANCE(expression, matcher)     \
  EXPECT_PERFORMANCE_IMPL(expression, matcher, 1UL)

namespace testing::perf {
using Clock = std::chrono::high_resolution_clock;

template <typename> struct DurationImpl {
  using type = std::chrono::nanoseconds;
};

template <typename Rep, typename Ratio>
struct DurationImpl<std::chrono::duration<Rep, Ratio>> {
  using type = std::chrono::duration<Rep, Ratio>;
};

template <typename Duration>
struct PerformanceTestDuration {
  Clock::duration average() const { return (ticks.back() - ticks.front()) / size(); }
  operator Duration() const {
    return std::chrono::duration_cast<Duration>(ticks.back() - ticks.front());
  }

  size_t size() const { return ticks.size() - 1; }
  Duration operator()(size_t i = 0) const {
    return std::chrono::duration_cast<Duration>(ticks.at(i + 1) - ticks.at(i));
  }
  void lap() { ticks.push_back(Clock::now()); }
  
  std::vector<Clock::time_point> ticks{};
};

template <typename Duration>
void PrintTo(PerformanceTestDuration<Duration> const &ptd, std::ostream *os) {
  (*os) << "duration: " << static_cast<Duration>(ptd);
  if (size_t const n = ptd.size(); n > 1) {
    [[maybe_unused]] int const digits = n == 1 ? 1 : std::log10(n - 1) + 1;
    double X = 0, X2 = 0;
    
    for (size_t i = 0; i < n; ++i) {
      auto d = ptd(i);
      X += d.count();
      X2 += std::pow(d.count(), 2);
#     if defined(PERFORMANCE_TEST_PRINT_LAPS)
        (*os) << "\nlap " << std::setw(digits) << i << ": " << d;
#     endif
    }
    
    long long E = X / n;
    long long S = std::sqrt(X2 / n - std::pow(X / n, 2));
    (*os) << "\naverage: " << Duration(E);
    (*os) << "\nstd.dev: " << Duration(S);
  }
}

template <typename> struct first_type {
  using type = Clock::duration;
};

template <template <typename...> class Template, typename Arg0, typename Arg1, typename... Args>
struct first_type<Template<Arg0, Arg1, Args...>> {
  using type = std::decay_t<Arg1>;
};

template <typename T> using first_type_t = typename first_type<T>::type;

MATCHER_P(FasterThan, limit, "is < " + testing::PrintToString(limit)) {
  return arg.average() < limit;
}

MATCHER_P2(BetweenTimes, low, high,
          "is between " + testing::PrintToString(low) + " and " +
           testing::PrintToString(high)) {
  return arg.average() < high && arg.average() > low;
}

MATCHER_P2(OnAverage, n, m,
           (n == 1 ? "" : "on average ") + DescribeMatcher<arg_type>(m)) {
  return testing::Matcher<arg_type>(m).MatchAndExplain(arg, result_listener);
}
}

#define EXPECT_PERFORMANCE_IMPL(expression, matcher, n_reps) \
  do {                                                       \
    using namespace testing::perf;                           \
    using namespace std::literals::chrono_literals;          \
                                                             \
    using duration_t = first_type_t<decltype(matcher)>;      \
    PerformanceTestDuration<duration_t> duration;            \
                                                             \
    for (size_t i = 0; i < n_reps; ++i) {                    \
      duration.lap();                                        \
      (void) expression;                                     \
    }                                                        \
    duration.lap();                                          \
                                                             \
    EXPECT_THAT(duration, OnAverage(n_reps, matcher));       \
  } while (false)


#define TEST_PERF_IMPL(test_suite_name, test_name, parent_class, limit) \
  class PERF_TEST_CLASS(test_suite_name) : public parent_class {        \
  protected:                                                            \
    void TestImpl();                                                    \
  };                                                                    \
  TEST_F(PERF_TEST_CLASS(test_suite_name), test_name) {                 \
    EXPECT_PERFORMANCE(TestImpl(), limit);                              \
  }                                                                     \
  void PERF_TEST_CLASS(test_suite_name)::TestImpl()