#include <barrier>
#include <doctest/doctest.h>
#include <latch>
#include <thread>
#include <vector>

#include "reference.hpp"

namespace {
struct TestObject {
  int value;
  explicit TestObject(int v) : value(v) {}
};

struct Node {
  int data;
  Ref<Node> next;
  WeakRef<Node> parent;

  explicit Node(int d) : data(d) {}
};
} // anonymous namespace

TEST_CASE("Ref basic functionality") {
  SUBCASE("make_ref creates valid Ref") {
    auto ref = make_ref<TestObject>(42);
    CHECK(ref);
    CHECK(ref.get() != nullptr);
    CHECK(ref->value == 42);
    CHECK((*ref).value == 42);
  }

  SUBCASE("copy construction increments reference count") {
    auto ref1 = make_ref<TestObject>(123);
    auto ref2 = ref1;

    CHECK(ref1);
    CHECK(ref2);
    CHECK(ref1.get() == ref2.get());
    CHECK(ref1->value == 123);
    CHECK(ref2->value == 123);
  }

  SUBCASE("copy assignment works correctly") {
    auto ref1 = make_ref<TestObject>(100);
    auto ref2 = make_ref<TestObject>(200);

    ref2 = ref1;
    CHECK(ref1.get() == ref2.get());
    CHECK(ref1->value == 100);
    CHECK(ref2->value == 100);
  }

  SUBCASE("move construction transfers ownership") {
    auto ref1 = make_ref<TestObject>(456);
    auto *ptr = ref1.get();
    auto ref2 = std::move(ref1);

    CHECK(!ref1);
    CHECK(ref2);
    CHECK(ref2.get() == ptr);
    CHECK(ref2->value == 456);
  }

  SUBCASE("move assignment transfers ownership") {
    auto ref1 = make_ref<TestObject>(789);
    auto ref2 = make_ref<TestObject>(999);
    auto *ptr = ref1.get();

    ref2 = std::move(ref1);
    CHECK(!ref1);
    CHECK(ref2);
    CHECK(ref2.get() == ptr);
    CHECK(ref2->value == 789);
  }

  SUBCASE("reset clears reference") {
    auto ref = make_ref<TestObject>(111);
    CHECK(ref);

    ref.reset();
    CHECK(!ref);
    CHECK(ref.get() == nullptr);
  }
}

TEST_CASE("WeakRef basic functionality") {
  SUBCASE("construction from Ref") {
    auto ref = make_ref<TestObject>(333);
    WeakRef<TestObject> weak_ref = ref;

    auto locked = weak_ref.lock();
    CHECK(locked);
    CHECK(locked.get() == ref.get());
    CHECK(locked->value == 333);
  }

  SUBCASE("lock() returns empty when object destroyed") {
    WeakRef<TestObject> weak_ref;
    {
      auto ref = make_ref<TestObject>(444);
      weak_ref = ref;
    }
    // ref goes out of scope, object should be destroyed

    auto locked = weak_ref.lock();
    CHECK(!locked);
  }

  SUBCASE("copy and move semantics") {
    auto ref = make_ref<TestObject>(666);
    WeakRef<TestObject> weak1 = ref;
    WeakRef<TestObject> weak2 = weak1;            // copy
    WeakRef<TestObject> weak3 = std::move(weak1); // move

    auto locked2 = weak2.lock();
    auto locked3 = weak3.lock();
    CHECK(locked2);
    CHECK(locked3);
    CHECK(locked2->value == 666);
    CHECK(locked3->value == 666);
  }
}

TEST_CASE("Ref thread safety") {
  SUBCASE("concurrent copying") {
    const int num_threads = 4;
    const int copies_per_thread = 100;
    const int test_iterations = 1000;

    for (int iter = 0; iter < test_iterations; ++iter) {
      auto ref = make_ref<TestObject>(777);
      std::vector<std::thread> threads;
      std::latch start_latch{num_threads + 1};

      for (int i = 0; i < num_threads; ++i) {
        threads.emplace_back([&]() {
          start_latch.arrive_and_wait();

          for (int j = 0; j < copies_per_thread; ++j) {
            auto copy = ref;
            CHECK(copy);
            CHECK(copy->value == 777);
          }
        });
      }

      start_latch.arrive_and_wait();

      for (auto &t : threads) {
        t.join();
      }

      CHECK(ref);
      CHECK(ref->value == 777);
    }
  }
}

TEST_CASE("Control block cleanup race condition test") {
  // This test specifically targets the race condition where both
  // the last strong reference and last weak reference are destroyed
  // simultaneously, potentially causing double-free of control block

  const int test_iterations = 10000;

  // Shared state for passing references between threads
  Ref<TestObject> ptr1;
  WeakRef<TestObject> ptr2;
  auto setup = [&]() {
    ptr1 = make_ref<TestObject>(0);
    ptr2 = ptr1;
  };

  // Barrier for synchronization - 2 participants (main thread + worker thread)
  std::barrier sync_barrier{2};

  std::thread worker_thread([&]() {
    for (int iter = 0; iter < test_iterations; ++iter) {
      // Wait for main thread to create the references
      sync_barrier.arrive_and_wait();

      // Worker thread destroys the weak reference simultaneously with main
      // thread
      ptr2.reset();

      // Wait for next iteration
      sync_barrier.arrive_and_wait();
    }
  });

  for (int iter = 0; iter < test_iterations; ++iter) {
    // Create references
    setup();

    // Both threads are ready - synchronize for simultaneous destruction
    sync_barrier.arrive_and_wait();

    // Main thread destroys the strong reference at the same time
    // as worker thread destroys the weak reference
    ptr1.reset();

    // Wait for both destructions to complete
    sync_barrier.arrive_and_wait();

    // Clean up for next iteration
    ptr1.reset();
    ptr2.reset();
  }

  worker_thread.join();

  // If we reach here without segfault/double-free, the test passes
  // The bug would manifest as a crash or memory corruption
}

TEST_CASE("WeakRef prevents circular references") {
  SUBCASE("simple weak reference lifecycle") {
    WeakRef<TestObject> weak_ref;

    // Create object and weak reference
    {
      auto ref = make_ref<TestObject>(123);
      weak_ref = ref;

      // Should be able to lock while object exists
      auto locked = weak_ref.lock();
      CHECK(locked);
      CHECK(locked->value == 123);
    }
    // Object destroyed when ref goes out of scope

    // Should not be able to lock after object destroyed
    auto locked = weak_ref.lock();
    CHECK(!locked);
  }

  SUBCASE("parent-child cycle with WeakRef breaks cycle") {
    auto parent = make_ref<Node>(1);
    auto child = make_ref<Node>(2);

    // Create potential cycle
    parent->next = child;   // Strong reference: parent → child
    child->parent = parent; // WeakRef: child ⇝ parent (breaks cycle)

    CHECK(parent->data == 1);
    CHECK(child->data == 2);
    CHECK(parent->next == child);

    // Verify weak reference works while parent exists
    CHECK(child->parent.lock() == parent);

    // Clear the only strong reference to parent
    parent.reset(); // This should destroy the parent object

    // Now child's weak reference should fail to lock since parent is destroyed
    CHECK(!child->parent.lock());
  }
}