/// DX12Renderer - DirectX 12 rendering backend implementation
/// This is a PLATFORM-SPECIFIC module (DirectX 12 API on Windows)

import Foundation
import RendererAPI

#if os(Windows)
// Note: In a real implementation, this would import DirectX 12 C bindings
// import CDirectX12 or similar Swift DirectX wrapper
#endif

/// DirectX 12-based renderer implementation
public final class DX12Renderer: Renderer, @unchecked Sendable {
    
    private var config: RendererConfig?
    private var isInitialized: Bool = false
    
    // DirectX 12 handles (placeholders - would be actual D3D12 types)
    private var device: UnsafeMutableRawPointer?
    private var commandQueue: UnsafeMutableRawPointer?
    private var swapChain: UnsafeMutableRawPointer?
    private var rtvHeap: UnsafeMutableRawPointer? // Render Target View heap
    private var dsvHeap: UnsafeMutableRawPointer? // Depth Stencil View heap
    private var commandAllocator: UnsafeMutableRawPointer?
    private var commandList: UnsafeMutableRawPointer?
    private var pipelineState: UnsafeMutableRawPointer?
    private var rootSignature: UnsafeMutableRawPointer?
    
    // Synchronization
    private var fence: UnsafeMutableRawPointer?
    private var fenceValue: UInt64 = 0
    private var fenceEvent: UnsafeMutableRawPointer?
    
    // Resource storage
    private var meshes: [MeshHandle: DX12Mesh] = [:]
    private var textures: [TextureHandle: DX12Texture] = [:]
    private var materials: [MaterialHandle: DX12Material] = [:]
    
    private var currentFrameIndex: UInt32 = 0
    private let maxFramesInFlight: UInt32 = 2
    
    public init() {
        print("    🪟 DX12Renderer created")
    }
    
    // MARK: - Renderer Protocol Implementation
    
    public func initialize(config: RendererConfig) async throws {
        print("    → Initializing DirectX 12 renderer...")
        self.config = config
        
        #if os(Windows)
        // 1. Enable debug layer in debug builds
        try enableDebugLayer()
        
        // 2. Create DXGI Factory
        try createFactory()
        
        // 3. Create D3D12 Device
        try createDevice()
        
        // 4. Create Command Queue
        try createCommandQueue()
        
        // 5. Create Swap Chain
        try createSwapChain(windowHandle: config.windowHandle, width: config.width, height: config.height)
        
        // 6. Create Descriptor Heaps
        try createDescriptorHeaps()
        
        // 7. Create Render Target Views
        try createRenderTargets()
        
        // 8. Create Command Allocator and List
        try createCommandAllocatorAndList()
        
        // 9. Create Root Signature
        try createRootSignature()
        
        // 10. Create Pipeline State Object (PSO)
        try createPipelineState()
        
        // 11. Create Fence for synchronization
        try createFence()
        #else
        throw RendererError.unsupportedPlatform("DirectX 12 is only available on Windows")
        #endif
        
        isInitialized = true
        print("    ✓ DirectX 12 renderer initialized")
    }
    
    public func beginFrame() throws {
        guard isInitialized else { throw RendererError.notInitialized }
        
        #if os(Windows)
        // Wait for previous frame
        // Reset command allocator
        // Reset command list
        // Set render target
        // Clear render target and depth buffer
        #endif
    }
    
    public func draw(scene: Scene) throws {
        guard isInitialized else { throw RendererError.notInitialized }
        
        #if os(Windows)
        // Set root signature
        // Set pipeline state
        // Set viewport and scissor rect
        
        // Draw each entity
        for entity in scene.entities {
            // Set root parameters (CBV/SRV/UAV)
            // Set vertex and index buffers
            // Draw indexed
            drawEntity(entity, camera: scene.camera)
        }
        #endif
    }
    
    public func endFrame() throws {
        guard isInitialized else { throw RendererError.notInitialized }
        
        #if os(Windows)
        // Transition render target to present state
        // Close command list
        // Execute command list on queue
        // Present swap chain
        // Signal fence
        
        currentFrameIndex = (currentFrameIndex + 1) % maxFramesInFlight
        #endif
    }
    
    public func shutdown() async {
        print("    → Shutting down DirectX 12 renderer...")
        
        #if os(Windows)
        // Wait for GPU to finish
        // Destroy all resources in reverse order
        destroyFence()
        destroyPipelineState()
        destroyRootSignature()
        destroyCommandResources()
        destroyRenderTargets()
        destroyDescriptorHeaps()
        destroySwapChain()
        destroyCommandQueue()
        destroyDevice()
        #endif
        
        isInitialized = false
        print("    ✓ DirectX 12 renderer shutdown complete")
    }
    
    public func loadMesh(vertices: [Vertex], indices: [UInt32]) async throws -> MeshHandle {
        let handle = MeshHandle()
        
        #if os(Windows)
        // Create D3D12 vertex buffer (committed resource)
        // Create D3D12 index buffer (committed resource)
        // Upload data to GPU using upload heap
        #endif
        
        let dx12Mesh = DX12Mesh(
            vertexBuffer: nil,
            indexBuffer: nil,
            vertexBufferView: nil,
            indexBufferView: nil,
            indexCount: UInt32(indices.count)
        )
        
        meshes[handle] = dx12Mesh
        return handle
    }
    
    public func loadTexture(data: Data, width: Int, height: Int, format: TextureFormat) async throws -> TextureHandle {
        let handle = TextureHandle()
        
        #if os(Windows)
        // Create D3D12 texture resource
        // Create Shader Resource View (SRV)
        // Upload texture data via upload heap
        #endif
        
        let dx12Texture = DX12Texture(
            resource: nil,
            srvHeapIndex: 0,
            width: width,
            height: height
        )
        
        textures[handle] = dx12Texture
        return handle
    }
    
    public func createMaterial(albedoTexture: TextureHandle?, normalTexture: TextureHandle?) async throws -> MaterialHandle {
        let handle = MaterialHandle()
        
        #if os(Windows)
        // Create material constant buffer
        // Set up descriptor table for textures
        #endif
        
        let dx12Material = DX12Material(
            constantBuffer: nil,
            albedoTexture: albedoTexture,
            normalTexture: normalTexture
        )
        
        materials[handle] = dx12Material
        return handle
    }
    
    public var info: RendererInfo {
        return RendererInfo(
            apiName: "DirectX 12",
            apiVersion: "12.0",
            deviceName: "D3D12 Device (placeholder)",
            maxTextureSize: 16384
        )
    }
    
    // MARK: - DirectX 12-Specific Implementation
    
    #if os(Windows)
    
    private func enableDebugLayer() throws {
        print("      • Enabling D3D12 debug layer...")
        // ID3D12Debug::EnableDebugLayer()
    }
    
    private func createFactory() throws {
        print("      • Creating DXGI factory...")
        // CreateDXGIFactory2(...)
    }
    
    private func createDevice() throws {
        print("      • Creating D3D12 device...")
        // D3D12CreateDevice(...) with hardware adapter
    }
    
    private func createCommandQueue() throws {
        print("      • Creating command queue...")
        // ID3D12Device::CreateCommandQueue(D3D12_COMMAND_LIST_TYPE_DIRECT)
    }
    
    private func createSwapChain(windowHandle: UnsafeMutableRawPointer?, width: Int, height: Int) throws {
        print("      • Creating swap chain (\(width)x\(height))...")
        // IDXGIFactory::CreateSwapChainForHwnd(...)
    }
    
    private func createDescriptorHeaps() throws {
        print("      • Creating descriptor heaps...")
        // ID3D12Device::CreateDescriptorHeap for RTV, DSV, CBV/SRV/UAV
    }
    
    private func createRenderTargets() throws {
        print("      • Creating render target views...")
        // ID3D12Device::CreateRenderTargetView for each swap chain buffer
    }
    
    private func createCommandAllocatorAndList() throws {
        print("      • Creating command allocator and list...")
        // ID3D12Device::CreateCommandAllocator
        // ID3D12Device::CreateCommandList
    }
    
    private func createRootSignature() throws {
        print("      • Creating root signature...")
        // ID3D12Device::CreateRootSignature with CBVs, SRVs, samplers
    }
    
    private func createPipelineState() throws {
        print("      • Creating pipeline state...")
        // Compile HLSL shaders
        // ID3D12Device::CreateGraphicsPipelineState with shaders and state
    }
    
    private func createFence() throws {
        print("      • Creating fence...")
        // ID3D12Device::CreateFence
        // CreateEventEx for CPU-side waiting
    }
    
    private func drawEntity(_ entity: Entity, camera: Camera) {
        // ID3D12GraphicsCommandList::SetGraphicsRootConstantBufferView (MVP matrix)
        // ID3D12GraphicsCommandList::SetGraphicsRootDescriptorTable (textures)
        // ID3D12GraphicsCommandList::IASetVertexBuffers
        // ID3D12GraphicsCommandList::IASetIndexBuffer
        // ID3D12GraphicsCommandList::DrawIndexedInstanced
    }
    
    // MARK: - Cleanup
    
    private func destroyFence() {
        // CloseHandle(fenceEvent)
        // fence->Release()
    }
    
    private func destroyPipelineState() {
        // pipelineState->Release()
    }
    
    private func destroyRootSignature() {
        // rootSignature->Release()
    }
    
    private func destroyCommandResources() {
        // commandList->Release()
        // commandAllocator->Release()
    }
    
    private func destroyRenderTargets() {
        // Release all RTV resources
    }
    
    private func destroyDescriptorHeaps() {
        // rtvHeap->Release()
        // dsvHeap->Release()
    }
    
    private func destroySwapChain() {
        // swapChain->Release()
    }
    
    private func destroyCommandQueue() {
        // commandQueue->Release()
    }
    
    private func destroyDevice() {
        // device->Release()
    }
    
    #endif
}

// MARK: - DirectX 12 Resource Types

private struct DX12Mesh {
    var vertexBuffer: UnsafeMutableRawPointer?
    var indexBuffer: UnsafeMutableRawPointer?
    var vertexBufferView: UnsafeMutableRawPointer?
    var indexBufferView: UnsafeMutableRawPointer?
    var indexCount: UInt32
}

private struct DX12Texture {
    var resource: UnsafeMutableRawPointer?
    var srvHeapIndex: Int
    var width: Int
    var height: Int
}

private struct DX12Material {
    var constantBuffer: UnsafeMutableRawPointer?
    var albedoTexture: TextureHandle?
    var normalTexture: TextureHandle?
}

// MARK: - Errors

private enum RendererError: Error {
    case notInitialized
    case unsupportedPlatform(String)
    case dx12Error(String)
}