/**
 * @file test_mutex.cpp
 * @brief Comprehensive unit tests for ipc::sync::mutex class
 * 
 * This test suite covers:
 * - Mutex construction (default and named)
 * - Lock/unlock operations
 * - Try-lock functionality
 * - Timed lock with timeout
 * - Named mutex for inter-process synchronization
 * - Resource cleanup (clear, clear_storage)
 * - Native handle access
 * - Concurrent access scenarios
 */

#include <gtest/gtest.h>
#include <thread>
#include <chrono>
#include <atomic>
#include <vector>
#include "libipc/mutex.h"
#include "libipc/def.h"

using namespace ipc;
using namespace ipc::sync;

namespace {

// Generate unique mutex names for tests
std::string generate_unique_mutex_name(const char* prefix) {
  static int counter = 0;
  return std::string(prefix) + "_mutex_" + std::to_string(++counter);
}

} // anonymous namespace

class MutexTest : public ::testing::Test {
protected:
  void TearDown() override {
      // Allow time for cleanup
      std::this_thread::sleep_for(std::chrono::milliseconds(10));
  }
};

// Test default constructor
TEST_F(MutexTest, DefaultConstructor) {
  mutex mtx;
  // Default constructed mutex may or may not be valid depending on implementation
  // Just ensure it doesn't crash
}

// Test named constructor
TEST_F(MutexTest, NamedConstructor) {
  std::string name = generate_unique_mutex_name("named_ctor");
  
  mutex mtx(name.c_str());
  EXPECT_TRUE(mtx.valid());
}

// Test native() const method
TEST_F(MutexTest, NativeConst) {
  std::string name = generate_unique_mutex_name("native_const");
  
  const mutex mtx(name.c_str());
  const void* native_handle = mtx.native();
  
  EXPECT_NE(native_handle, nullptr);
}

// Test native() non-const method
TEST_F(MutexTest, NativeNonConst) {
  std::string name = generate_unique_mutex_name("native_nonconst");
  
  mutex mtx(name.c_str());
  void* native_handle = mtx.native();
  
  EXPECT_NE(native_handle, nullptr);
}

// Test valid() method
TEST_F(MutexTest, Valid) {
  mutex mtx1;
  // May or may not be valid without open
  
  std::string name = generate_unique_mutex_name("valid");
  mutex mtx2(name.c_str());
  EXPECT_TRUE(mtx2.valid());
}

// Test open() method
TEST_F(MutexTest, Open) {
  std::string name = generate_unique_mutex_name("open");
  
  mutex mtx;
  bool result = mtx.open(name.c_str());
  
  EXPECT_TRUE(result);
  EXPECT_TRUE(mtx.valid());
}

// Test close() method
TEST_F(MutexTest, Close) {
  std::string name = generate_unique_mutex_name("close");
  
  mutex mtx(name.c_str());
  ASSERT_TRUE(mtx.valid());
  
  mtx.close();
  EXPECT_FALSE(mtx.valid());
}

// Test clear() method
TEST_F(MutexTest, Clear) {
  std::string name = generate_unique_mutex_name("clear");
  
  mutex mtx(name.c_str());
  ASSERT_TRUE(mtx.valid());
  
  mtx.clear();
  EXPECT_FALSE(mtx.valid());
}

// Test clear_storage() static method
TEST_F(MutexTest, ClearStorage) {
  std::string name = generate_unique_mutex_name("clear_storage");
  
  {
      mutex mtx(name.c_str());
      EXPECT_TRUE(mtx.valid());
  }
  
  mutex::clear_storage(name.c_str());
  
  // Try to open after clear - should create new or fail gracefully
  mutex mtx2(name.c_str());
}

// Test basic lock and unlock
TEST_F(MutexTest, LockUnlock) {
  std::string name = generate_unique_mutex_name("lock_unlock");
  
  mutex mtx(name.c_str());
  ASSERT_TRUE(mtx.valid());
  
  bool locked = mtx.lock();
  EXPECT_TRUE(locked);
  
  bool unlocked = mtx.unlock();
  EXPECT_TRUE(unlocked);
}

// Test try_lock
TEST_F(MutexTest, TryLock) {
  std::string name = generate_unique_mutex_name("try_lock");
  
  mutex mtx(name.c_str());
  ASSERT_TRUE(mtx.valid());
  
  bool locked = mtx.try_lock();
  EXPECT_TRUE(locked);
  
  if (locked) {
      mtx.unlock();
  }
}

// Test timed lock with infinite timeout
TEST_F(MutexTest, TimedLockInfinite) {
  std::string name = generate_unique_mutex_name("timed_lock_inf");
  
  mutex mtx(name.c_str());
  ASSERT_TRUE(mtx.valid());
  
  bool locked = mtx.lock(invalid_value);
  EXPECT_TRUE(locked);
  
  if (locked) {
      mtx.unlock();
  }
}

// Test timed lock with timeout
TEST_F(MutexTest, TimedLockTimeout) {
  std::string name = generate_unique_mutex_name("timed_lock_timeout");
  
  mutex mtx(name.c_str());
  ASSERT_TRUE(mtx.valid());
  
  // Lock with 100ms timeout
  bool locked = mtx.lock(100);
  EXPECT_TRUE(locked);
  
  if (locked) {
      mtx.unlock();
  }
}

// Test mutex protects critical section
TEST_F(MutexTest, CriticalSection) {
  std::string name = generate_unique_mutex_name("critical_section");
  
  mutex mtx(name.c_str());
  ASSERT_TRUE(mtx.valid());
  
  int shared_counter = 0;
  const int iterations = 100;
  
  auto increment_task = [&]() {
      for (int i = 0; i < iterations; ++i) {
          mtx.lock();
          ++shared_counter;
          mtx.unlock();
      }
  };
  
  std::thread t1(increment_task);
  std::thread t2(increment_task);
  
  t1.join();
  t2.join();
  
  EXPECT_EQ(shared_counter, iterations * 2);
}

// Test concurrent try_lock
TEST_F(MutexTest, ConcurrentTryLock) {
  std::string name = generate_unique_mutex_name("concurrent_try");
  
  mutex mtx(name.c_str());
  ASSERT_TRUE(mtx.valid());
  
  std::atomic<int> success_count{0};
  std::atomic<int> fail_count{0};
  
  auto try_lock_task = [&]() {
      for (int i = 0; i < 10; ++i) {
          if (mtx.try_lock()) {
              ++success_count;
              std::this_thread::sleep_for(std::chrono::milliseconds(1));
              mtx.unlock();
          } else {
              ++fail_count;
          }
          std::this_thread::yield();
      }
  };
  
  std::thread t1(try_lock_task);
  std::thread t2(try_lock_task);
  std::thread t3(try_lock_task);
  
  t1.join();
  t2.join();
  t3.join();
  
  EXPECT_GT(success_count.load(), 0);
  // Some try_locks should succeed
}

// Test lock contention
TEST_F(MutexTest, LockContention) {
  std::string name = generate_unique_mutex_name("contention");
  
  mutex mtx(name.c_str());
  ASSERT_TRUE(mtx.valid());
  
  std::atomic<bool> thread1_in_cs{false};
  std::atomic<bool> thread2_in_cs{false};
  std::atomic<bool> violation{false};
  
  auto contention_task = [&](std::atomic<bool>& my_flag, 
                              std::atomic<bool>& other_flag) {
      for (int i = 0; i < 50; ++i) {
          mtx.lock();
          
          my_flag.store(true);
          if (other_flag.load()) {
              violation.store(true);
          }
          
          std::this_thread::sleep_for(std::chrono::microseconds(10));
          
          my_flag.store(false);
          mtx.unlock();
          
          std::this_thread::yield();
      }
  };
  
  std::thread t1(contention_task, std::ref(thread1_in_cs), std::ref(thread2_in_cs));
  std::thread t2(contention_task, std::ref(thread2_in_cs), std::ref(thread1_in_cs));
  
  t1.join();
  t2.join();
  
  // Should never have both threads in critical section
  EXPECT_FALSE(violation.load());
}

// Test multiple lock/unlock cycles
TEST_F(MutexTest, MultipleCycles) {
  std::string name = generate_unique_mutex_name("cycles");
  
  mutex mtx(name.c_str());
  ASSERT_TRUE(mtx.valid());
  
  for (int i = 0; i < 100; ++i) {
      ASSERT_TRUE(mtx.lock());
      ASSERT_TRUE(mtx.unlock());
  }
}

// Test timed lock timeout scenario
TEST_F(MutexTest, TimedLockTimeoutScenario) {
  std::string name = generate_unique_mutex_name("timeout_scenario");
  
  mutex mtx(name.c_str());
  ASSERT_TRUE(mtx.valid());
  
  // Lock in main thread
  ASSERT_TRUE(mtx.lock());
  
  std::atomic<bool> timeout_occurred{false};
  
  std::thread t([&]() {
      // Try to lock with short timeout - should timeout
      bool locked = mtx.lock(50); // 50ms timeout
      if (!locked) {
          timeout_occurred.store(true);
      } else {
          mtx.unlock();
      }
  });
  
  std::this_thread::sleep_for(std::chrono::milliseconds(100));
  mtx.unlock();
  
  t.join();
  
  // Timeout should have occurred since we held the lock
  EXPECT_TRUE(timeout_occurred.load());
}

// Test reopen after close
TEST_F(MutexTest, ReopenAfterClose) {
  std::string name = generate_unique_mutex_name("reopen");
  
  mutex mtx;
  
  ASSERT_TRUE(mtx.open(name.c_str()));
  EXPECT_TRUE(mtx.valid());
  
  mtx.close();
  EXPECT_FALSE(mtx.valid());
  
  ASSERT_TRUE(mtx.open(name.c_str()));
  EXPECT_TRUE(mtx.valid());
}

// Test named mutex inter-thread synchronization
TEST_F(MutexTest, NamedMutexInterThread) {
  std::string name = generate_unique_mutex_name("inter_thread");
  
  int shared_data = 0;
  std::atomic<bool> t1_done{false};
  std::atomic<bool> t2_done{false};
  
  std::thread t1([&]() {
      mutex mtx(name.c_str());
      ASSERT_TRUE(mtx.valid());
      
      mtx.lock();
      shared_data = 100;
      std::this_thread::sleep_for(std::chrono::milliseconds(50));
      mtx.unlock();
      
      t1_done.store(true);
  });
  
  std::thread t2([&]() {
      // Wait a bit to ensure t1 starts first
      std::this_thread::sleep_for(std::chrono::milliseconds(10));
      
      mutex mtx(name.c_str());
      ASSERT_TRUE(mtx.valid());
      
      mtx.lock();
      EXPECT_TRUE(t1_done.load() || shared_data == 100);
      shared_data = 200;
      mtx.unlock();
      
      t2_done.store(true);
  });
  
  t1.join();
  t2.join();
  
  EXPECT_EQ(shared_data, 200);
}

// Test exception safety of try_lock
TEST_F(MutexTest, TryLockExceptionSafety) {
  std::string name = generate_unique_mutex_name("try_lock_exception");
  
  mutex mtx(name.c_str());
  ASSERT_TRUE(mtx.valid());
  
  bool exception_thrown = false;
  try {
      mtx.try_lock();
  } catch (const std::system_error&) {
      exception_thrown = true;
  } catch (...) {
      FAIL() << "Unexpected exception type";
  }
  
  // try_lock may throw system_error
  // Just ensure we can handle it
}

// Test concurrent open/close operations
TEST_F(MutexTest, ConcurrentOpenClose) {
  std::vector<std::thread> threads;
  std::atomic<int> success_count{0};
  
  for (int i = 0; i < 5; ++i) {
      threads.emplace_back([&, i]() {
          std::string name = generate_unique_mutex_name("concurrent");
          name += std::to_string(i);
          
          mutex mtx;
          if (mtx.open(name.c_str())) {
              ++success_count;
              mtx.close();
          }
      });
  }
  
  for (auto& t : threads) {
      t.join();
  }
  
  EXPECT_EQ(success_count.load(), 5);
}

// Test mutex with zero timeout
TEST_F(MutexTest, ZeroTimeout) {
  std::string name = generate_unique_mutex_name("zero_timeout");
  
  mutex mtx(name.c_str());
  ASSERT_TRUE(mtx.valid());
  
  // Lock with zero timeout (should try once and return)
  bool locked = mtx.lock(0);
  
  if (locked) {
      mtx.unlock();
  }
  // Result may vary, just ensure it doesn't hang
}

// Test rapid lock/unlock sequence
TEST_F(MutexTest, RapidLockUnlock) {
  std::string name = generate_unique_mutex_name("rapid");
  
  mutex mtx(name.c_str());
  ASSERT_TRUE(mtx.valid());
  
  auto rapid_task = [&]() {
      for (int i = 0; i < 1000; ++i) {
          mtx.lock();
          mtx.unlock();
      }
  };
  
  std::thread t1(rapid_task);
  std::thread t2(rapid_task);
  
  t1.join();
  t2.join();
  
  // Should complete without deadlock or crash
}

// Test lock after clear
TEST_F(MutexTest, LockAfterClear) {
  std::string name = generate_unique_mutex_name("lock_after_clear");
  
  mutex mtx(name.c_str());
  ASSERT_TRUE(mtx.valid());
  
  mtx.lock();
  mtx.unlock();
  
  mtx.clear();
  EXPECT_FALSE(mtx.valid());
  
  // Attempting to lock after clear should fail gracefully
  bool locked = mtx.lock();
  EXPECT_FALSE(locked);
}