#include <gtest/gtest.h>

#include <XCEngine/Components/Component.h>
#include <XCEngine/Components/GameObject.h>
#include <XCEngine/Scene/RuntimeLoop.h>
#include <XCEngine/Scene/Scene.h>

#include <memory>
#include <string>

using namespace XCEngine::Components;

namespace {

struct RuntimeLoopCounters {
    int startCount = 0;
    int fixedUpdateCount = 0;
    int updateCount = 0;
    int lateUpdateCount = 0;
};

class RuntimeLoopObserverComponent : public Component {
public:
    explicit RuntimeLoopObserverComponent(RuntimeLoopCounters* counters)
        : m_counters(counters) {
    }

    std::string GetName() const override {
        return "RuntimeLoopObserver";
    }

    void Start() override {
        if (m_counters) {
            ++m_counters->startCount;
        }
    }

    void FixedUpdate() override {
        if (m_counters) {
            ++m_counters->fixedUpdateCount;
        }
    }

    void Update(float deltaTime) override {
        (void)deltaTime;
        if (m_counters) {
            ++m_counters->updateCount;
        }
    }

    void LateUpdate(float deltaTime) override {
        (void)deltaTime;
        if (m_counters) {
            ++m_counters->lateUpdateCount;
        }
    }

private:
    RuntimeLoopCounters* m_counters = nullptr;
};

class RuntimeLoopTest : public ::testing::Test {
protected:
    Scene* CreateScene(const std::string& name = "RuntimeLoopScene") {
        m_scene = std::make_unique<Scene>(name);
        return m_scene.get();
    }

    RuntimeLoopCounters counters;
    std::unique_ptr<Scene> m_scene;
};

TEST_F(RuntimeLoopTest, AccumulatesFixedUpdatesAcrossFramesAndRunsVariableUpdatesEveryTick) {
    RuntimeLoop loop({0.02f, 0.1f, 4});
    Scene* scene = CreateScene();
    GameObject* host = scene->CreateGameObject("Host");
    host->AddComponent<RuntimeLoopObserverComponent>(&counters);

    loop.Start(scene);

    loop.Tick(0.01f);
    EXPECT_EQ(counters.fixedUpdateCount, 0);
    EXPECT_EQ(counters.startCount, 1);
    EXPECT_EQ(counters.updateCount, 1);
    EXPECT_EQ(counters.lateUpdateCount, 1);

    loop.Tick(0.01f);
    EXPECT_EQ(counters.fixedUpdateCount, 1);
    EXPECT_EQ(counters.startCount, 1);
    EXPECT_EQ(counters.updateCount, 2);
    EXPECT_EQ(counters.lateUpdateCount, 2);
}

TEST_F(RuntimeLoopTest, ClampAndFixedStepLimitPreventExcessiveCatchUp) {
    RuntimeLoop loop({0.02f, 0.05f, 2});
    Scene* scene = CreateScene();
    GameObject* host = scene->CreateGameObject("Host");
    host->AddComponent<RuntimeLoopObserverComponent>(&counters);

    loop.Start(scene);
    loop.Tick(1.0f);

    EXPECT_EQ(counters.fixedUpdateCount, 2);
    EXPECT_EQ(counters.startCount, 1);
    EXPECT_EQ(counters.updateCount, 1);
    EXPECT_EQ(counters.lateUpdateCount, 1);
    EXPECT_NEAR(loop.GetFixedAccumulator(), 0.01f, 1e-4f);
}

TEST_F(RuntimeLoopTest, PauseSkipsAutomaticTicksUntilStepFrameIsRequested) {
    RuntimeLoop loop({0.02f, 0.1f, 4});
    Scene* scene = CreateScene();
    GameObject* host = scene->CreateGameObject("Host");
    host->AddComponent<RuntimeLoopObserverComponent>(&counters);

    loop.Start(scene);
    loop.Pause();

    loop.Tick(0.025f);
    EXPECT_EQ(counters.fixedUpdateCount, 0);
    EXPECT_EQ(counters.startCount, 0);
    EXPECT_EQ(counters.updateCount, 0);
    EXPECT_EQ(counters.lateUpdateCount, 0);

    loop.StepFrame();
    loop.Tick(0.025f);
    EXPECT_EQ(counters.fixedUpdateCount, 1);
    EXPECT_EQ(counters.startCount, 1);
    EXPECT_EQ(counters.updateCount, 1);
    EXPECT_EQ(counters.lateUpdateCount, 1);
    EXPECT_TRUE(loop.IsPaused());
}

TEST_F(RuntimeLoopTest, ResumeRestoresAutomaticTickProgressionAfterPause) {
    RuntimeLoop loop({0.02f, 0.1f, 4});
    Scene* scene = CreateScene();
    GameObject* host = scene->CreateGameObject("Host");
    host->AddComponent<RuntimeLoopObserverComponent>(&counters);

    loop.Start(scene);
    loop.Pause();
    loop.Tick(0.025f);
    EXPECT_EQ(counters.updateCount, 0);

    loop.Resume();
    EXPECT_FALSE(loop.IsPaused());
    loop.Tick(0.025f);

    EXPECT_EQ(counters.startCount, 1);
    EXPECT_EQ(counters.fixedUpdateCount, 1);
    EXPECT_EQ(counters.updateCount, 1);
    EXPECT_EQ(counters.lateUpdateCount, 1);
}

} // namespace