/// EngineCore - Platform-agnostic game engine core
/// NO PLATFORM-SPECIFIC IMPORTS ALLOWED IN THIS MODULE

import Foundation
import RendererAPI
import PhysicsEngine
import AssetLoader

// MARK: - Engine Configuration

/// Configuration for the game engine
public struct EngineConfig: Sendable {
    public var targetFrameRate: Int
    public var fixedTimeStep: Double
    public var maxFrameSkip: Int
    
    public init(targetFrameRate: Int = 60, fixedTimeStep: Double = 1.0/60.0, maxFrameSkip: Int = 5) {
        self.targetFrameRate = targetFrameRate
        self.fixedTimeStep = fixedTimeStep
        self.maxFrameSkip = maxFrameSkip
    }
}

// MARK: - Game Engine

/// Main game engine class - coordinates all subsystems
public actor GameEngine {
    
    // Platform abstraction layers (injected by platform-specific code)
    private let renderer: any Renderer
    private let windowManager: any WindowManager
    private let inputHandler: any InputHandler
    private let audioEngine: any AudioEngine
    
    // Core systems
    private let physicsEngine: PhysicsWorld
    private let assetLoader: AssetManager
    
    // Engine state
    private var isRunning: Bool = false
    private var config: EngineConfig
    
    // Scene management
    private var currentScene: Scene
    
    // Timing
    private var lastFrameTime: Double = 0
    private var accumulator: Double = 0
    private var frameCount: UInt64 = 0
    
    // MARK: - Initialization
    
    /// Initialize the engine with platform-specific abstractions
    public init(
        renderer: any Renderer,
        windowManager: any WindowManager,
        inputHandler: any InputHandler,
        audioEngine: any AudioEngine,
        config: EngineConfig = EngineConfig()
    ) {
        self.renderer = renderer
        self.windowManager = windowManager
        self.inputHandler = inputHandler
        self.audioEngine = audioEngine
        self.config = config
        
        // Initialize core systems (platform-agnostic)
        self.physicsEngine = PhysicsWorld()
        self.assetLoader = AssetManager()
        
        // Create default scene
        self.currentScene = Scene(
            entities: [],
            camera: Camera(),
            lights: []
        )
        
        print("🎮 SportsBallEngine initialized")
    }
    
    // MARK: - Engine Lifecycle
    
    /// Start the engine and run the main loop
    public func start() async throws {
        print("🚀 Starting engine...")
        
        // Initialize all systems
        try await initializeSystems()
        
        // Load initial scene/assets
        try await loadInitialScene()
        
        // Start the main loop
        isRunning = true
        lastFrameTime = getCurrentTime()
        
        print("✅ Engine started successfully")
        
        // Run the game loop
        await runMainLoop()
    }
    
    /// Stop the engine and cleanup
    public func stop() async {
        print("🛑 Stopping engine...")
        isRunning = false
        
        await shutdownSystems()
        
        print("✅ Engine stopped")
    }
    
    // MARK: - System Initialization
    
    private func initializeSystems() async throws {
        print("  → Initializing renderer...")
        let windowSize = windowManager.getSize()
        let rendererConfig = RendererConfig(
            windowHandle: windowManager.getNativeHandle(),
            width: windowSize.width,
            height: windowSize.height,
            vsyncEnabled: true,
            msaaSamples: 4
        )
        try await renderer.initialize(config: rendererConfig)
        print("    ✓ Renderer: \(renderer.info.apiName) \(renderer.info.apiVersion)")
        print("    ✓ Device: \(renderer.info.deviceName)")
        
        print("  → Initializing input system...")
        try await inputHandler.initialize()
        
        print("  → Initializing audio system...")
        try await audioEngine.initialize(config: AudioConfig())
        
        print("  → Initializing physics engine...")
        await physicsEngine.initialize()
        
        print("  → Initializing asset loader...")
        await assetLoader.initialize()
    }
    
    private func shutdownSystems() async {
        await renderer.shutdown()
        await inputHandler.shutdown()
        await audioEngine.shutdown()
        await physicsEngine.shutdown()
        await assetLoader.shutdown()
    }
    
    // MARK: - Main Game Loop (Carmack-style fixed timestep)
    
    private func runMainLoop() async {
        while isRunning {
            let currentTime = getCurrentTime()
            let frameTime = currentTime - lastFrameTime
            lastFrameTime = currentTime
            
            // Cap frame time to prevent spiral of death
            let clampedFrameTime = min(frameTime, config.fixedTimeStep * Double(config.maxFrameSkip))
            accumulator += clampedFrameTime
            
            // Process window events
            let windowEvents = windowManager.processEvents()
            for event in windowEvents {
                handleWindowEvent(event)
            }
            
            // Check if window should close
            if windowManager.shouldClose() {
                isRunning = false
                break
            }
            
            // Process input events
            let inputEvents = inputHandler.pollEvents()
            handleInputEvents(inputEvents)
            
            // Fixed timestep update loop (deterministic physics/gameplay)
            while accumulator >= config.fixedTimeStep {
                try? await fixedUpdate(deltaTime: Float(config.fixedTimeStep))
                accumulator -= config.fixedTimeStep
            }
            
            // Variable timestep render
            let alpha = Float(accumulator / config.fixedTimeStep)
            try? await render(interpolationAlpha: alpha)
            
            frameCount += 1
        }
    }
    
    // MARK: - Update & Render
    
    /// Fixed timestep update for physics and gameplay logic
    private func fixedUpdate(deltaTime: Float) async throws {
        // Update physics simulation
        await physicsEngine.step(deltaTime: deltaTime)
        
        // Update audio engine
        try audioEngine.update(deltaTime: deltaTime)
        
        // Update game logic (this would call game-specific code)
        updateGameLogic(deltaTime: deltaTime)
        
        // Sync physics state to scene entities
        syncPhysicsToScene()
    }
    
    /// Render the current frame
    private func render(interpolationAlpha: Float) async throws {
        try renderer.beginFrame()
        
        // Interpolate entity positions for smooth rendering
        let interpolatedScene = interpolateScene(currentScene, alpha: interpolationAlpha)
        
        // Draw the scene
        try renderer.draw(scene: interpolatedScene)
        
        try renderer.endFrame()
        try windowManager.swapBuffers()
    }
    
    // MARK: - Scene Management
    
    private func loadInitialScene() async throws {
        print("  → Loading initial scene...")
        
        // Create a simple test scene (stadium environment)
        let stadium = try await createStadiumScene()
        currentScene = stadium
        
        print("    ✓ Scene loaded: \(currentScene.entities.count) entities")
    }
    
    private func createStadiumScene() async throws -> Scene {
        // This would load actual assets, for now create a placeholder
        let camera = Camera(
            position: SIMD3<Float>(0, 10, 20),
            rotation: SIMD4<Float>(0, 0, 0, 1),
            fieldOfView: 60.0
        )
        
        let sunLight = Light(
            type: .directional,
            direction: SIMD3<Float>(-0.3, -1, -0.3),
            color: SIMD3<Float>(1, 0.95, 0.8),
            intensity: 1.0
        )
        
        return Scene(
            entities: [],
            camera: camera,
            lights: [sunLight]
        )
    }
    
    // MARK: - Event Handling
    
    private func handleWindowEvent(_ event: WindowEvent) {
        switch event {
        case .close:
            isRunning = false
        case .resize(let width, let height):
            print("  ↔ Window resized: \(width)x\(height)")
            // Notify renderer of resize
        case .focus(let focused):
            print("  👁 Window focus changed: \(focused)")
        case .minimize:
            print("  ⬇ Window minimized")
        case .maximize:
            print("  ⬆ Window maximized")
        case .restore:
            print("  ↕ Window restored")
        }
    }
    
    private func handleInputEvents(_ events: [InputEvent]) {
        for event in events {
            switch event {
            case .keyEvent(let key, let action):
                if key == .escape && action == .press {
                    isRunning = false
                }
            default:
                break
            }
        }
    }
    
    // MARK: - Game Logic
    
    private func updateGameLogic(deltaTime: Float) {
        // This is where sports game logic would go:
        // - Player AI
        // - Ball physics
        // - Animation state machines
        // - Collision detection
        // - Score tracking
        // etc.
    }
    
    private func syncPhysicsToScene() {
        // Sync physics simulation results back to scene entities
        // This would update entity transforms based on physics bodies
    }
    
    private func interpolateScene(_ scene: Scene, alpha: Float) -> Scene {
        // Interpolate between previous and current physics state for smooth rendering
        // For now, just return the scene as-is
        return scene
    }
    
    // MARK: - Public API
    
    public func loadScene(_ scene: Scene) {
        currentScene = scene
    }
    
    public func getFrameCount() -> UInt64 {
        return frameCount
    }
    
    public func getFPS() -> Double {
        // Calculate FPS based on frame timing
        return 60.0 // Placeholder
    }
    
    // MARK: - Utilities
    
    private func getCurrentTime() -> Double {
        return Double(DispatchTime.now().uptimeNanoseconds) / 1_000_000_000.0
    }
}