/*
 * gpu-instancing.cpp - GPU Instancing for UI Elements
 *
 * Production-ready example demonstrating:
 * - GPU instancing for batch UI rendering
 * - Shared material batches
 * - Efficient VR/AR UI rendering
 * - Low-latency UI updates
 * - DOTS-style data-oriented UI architecture
 *
 * © 2026 - Agent Guardrails Template
 */

#include "CoreMinimal.h"
#include "RenderCore/GPUInstancer.h"
#include "CommonUI/CommonUserWidget.h"
#include "Spatial/VolumetricRenderer.h"
#include "DDA/DDAManager.h"

namespace AgentGuardrails::UnrealUI
{

/**
 * GPU Instancing Manager for UI Elements
 * Batch renders UI components with shared materials
 * Efficient rendering for VR/AR environments
 */
class UGPUInstancingManager : public UObject
{
    GENERATED_BODY()

private:
    GPUInstancer* gpuInstancer;
    VolumetricRenderer* volumetricRenderer;
    DDAManager* ddaManager;

    TArray<UIInstance> uiInstances;
    UMaterialInstance* sharedMaterial;

public:
    void Initialize()
    {
        gpuInstancer = GPUInstancer::GetInstance();
        volumetricRenderer = VolumetricRenderer::GetInstance();
        ddaManager = DDAManager::GetInstance();

        // Create shared material for UI instancing
        sharedMaterial = CreateMaterialInstance("UISharedMaterial");
    }

    /**
     * Batch renders UI elements through GPU instancing
     * Efficient rendering for large UI hierarchies
     */
    void RenderUIBatch(TArray<UCommonUserWidget*> widgets)
    {
        // Build instancing data
        uiInstances.Reset();
        for (auto* widget : widgets)
        {
            UIInstance instance;
            instance.Position = widget->GetPosition();
            instance.Scale = widget->GetScale();
            instance.Color = widget->GetColor();
            instance.Depth = widget->GetDepth();
            instance.Material = sharedMaterial;

            uiInstances.Add(instance);
        }

        // Submit batch to GPU instancer
        gpuInstancer->RenderBatch(sharedMaterial, uiInstances);
    }

    /**
     * Creates UI instance data for GPU rendering
     */
    UIInstance CreateUIInstance(UCommonUserWidget* widget)
    {
        UIInstance instance;
        instance.Position = widget->GetPosition();
        instance.Scale = widget->GetScale();
        instance.Color = widget->GetColor();
        instance.Depth = widget->GetDepth();
        instance.Material = sharedMaterial;
        instance.IsVolumetric = widget->IsVolumetric();
        instance.IsHolographic = widget->IsHolographic();

        return instance;
    }

    /**
     * Enables GPU instancing for widget
     * Batch rendering optimization
     */
    void EnableGPUInstancing(UCommonUserWidget* widget)
    {
        widget->EnableGPUInstancing(true);
        widget->SetMaterial(sharedMaterial);
    }

    /**
     * Updates instanced UI based on DDA tier
     * Reduces batch complexity for stressed players
     */
    void UpdateForDDATier(DDAManager::EDifficultyTier tier)
    {
        switch (tier)
        {
            case DDAManager::EDifficultyTier::Difficult:
                // Stressed players: reduce batch count
                SetBatchCount(50);
                SetVolumetricIntensity(0.5f);
                break;

            case DDAManager::EDifficultyTier::Normal:
                // Standard batch count
                SetBatchCount(100);
                SetVolumetricIntensity(1.0f);
                break;

            case DDAManager::EDifficultyTier::Relaxed:
                // Engaged players: enhanced batching
                SetBatchCount(200);
                SetVolumetricIntensity(1.2f);
                break;
        }
    }

    /**
     * Sets batch count for GPU instancing
     */
    void SetBatchCount(int32 count)
    {
        gpuInstancer->SetMaxBatchCount(count);
    }

    /**
     * Sets volumetric intensity for instanced widgets
     */
    void SetVolumetricIntensity(float intensity)
    {
        volumetricRenderer->SetIntensity(intensity);
    }

    /**
     * Prefetches UI instances for upcoming scene
     * Predictive batching for performance
     */
    void PrefetchUIInstances(int32 predictedCount)
    {
        uiInstances.Reserve(predictedCount);
        for (int32 i = 0; i < predictedCount; i++)
        {
            UIInstance instance;
            instance.Position = FVector::Zero();
            instance.Scale = FVector2D::Zero();
            instance.Color = FColor::Transparent;
            instance.IsPrefetched = true;

            uiInstances.Add(instance);
        }
    }

    /**
     * Clears prefetched instances
     * Memory cleanup after scene transition
     */
    void ClearPrefetchedInstances()
    {
        uiInstances.RemoveAll([](const UIInstance& instance) {
            return instance.IsPrefetched == true;
        });
    }
};

/**
 * UI Instance data structure for GPU instancing
 */
USTRUCT()
struct UIInstance
{
    GENERATED_BODY()

    FVector Position;           // World position
    FVector2D Scale;            // UI scale
    FColor Color;               // Tint color
    float Depth;                // Z-depth for volumetric
    UMaterialInstance* Material; // Shared material
    bool IsVolumetric;          // Volumetric rendering enabled
    bool IsHolographic;         // Holographic rendering enabled
    bool IsPrefetched;          // Prefetched instance
};

/**
 * GPU Instancer for batch UI rendering
 */
class GPUInstancer
{
private:
    static GPUInstancer* instance;
    int32 maxBatchCount = 100;

public:
    static GPUInstancer* GetInstance()
    {
        if (!instance)
        {
            instance = new GPUInstancer();
        }
        return instance;
    }

    /**
     * Renders batch of UI instances
     * Single GPU call for all elements
     */
    void RenderBatch(UMaterialInstance* material, TArray<UIInstance>& instances)
    {
        // Create command buffer for batch render
        auto* commandBuffer = new FRenderCommandBuffer();

        // Submit instanced draw call
        commandBuffer->DrawInstanced(
            material,
            instances,
            instances.Size()
        );

        // Execute command buffer
        commandBuffer->Execute();
    }

    /**
     * Sets maximum batch count
     */
    void SetMaxBatchCount(int32 count)
    {
        maxBatchCount = count;
    }

    /**
     * Gets current batch count
     */
    int32 GetMaxBatchCount() const
    {
        return maxBatchCount;
    }
};

/**
 * Material instance factory for UI instancing
 */
UMaterialInstance* CreateMaterialInstance(const FString& materialName)
{
    auto* material = LoadObject<UMaterial>(nullptr, materialName);
    return material->CreateMaterialInstance();
}

/**
 * Batch UI rendering utilities
 */
namespace GPUInstancingUtils
{
    /**
     * Creates batch render command
     */
    FRenderCommandBuffer* CreateBatchRenderCommand(
        UMaterialInstance* material,
        TArray<UIInstance>& instances
    )
    {
        auto* commandBuffer = new FRenderCommandBuffer();
        commandBuffer->DrawInstanced(material, instances, instances.Size());
        return commandBuffer;
    }

    /**
     * Validates instance data for GPU rendering
     */
    bool ValidateInstance(const UIInstance& instance)
    {
        return instance.Material != nullptr &&
               instance.Color.Alpha > 0.0f;
    }

    /**
     * Optimizes instance array for batching
     */
    void OptimizeInstanceArray(TArray<UIInstance>& instances)
    {
        // Remove invalid instances
        instances.RemoveAll([](const UIInstance& instance) {
            return !ValidateInstance(instance);
        });

        // Sort by material for efficient batching
        instances.SortBy([](const UIInstance& instance) {
            return instance.Material->GetUniqueID();
        });
    }
}

} // namespace AgentGuardrails::UnrealUI