package me.hammerle.snuviengine.api;

import org.lwjgl.glfw.*;
import org.lwjgl.opengl.*;
import static org.lwjgl.glfw.Callbacks.*;
import static org.lwjgl.glfw.GLFW.*;
import static org.lwjgl.opengl.GL11.*;
import static org.lwjgl.system.MemoryUtil.*;

public abstract class Engine
{
    private static final String VERSION = "0.0.1";   
    public static final int TILE_SIZE = 16;
    public static final float SCALE = 2.0f;
    
    private long window;
    
    private int fpsIndex = 0;
    private final long[] fps = new long[100];
    private long fpsSum = 0;
    private double currentFps = 0;
    
    private int tpsIndex = 0;
    private final long[] tps = new long[100];
    private long tpsSum = 0;
    private double currentTps = 0;
    
    private long nanosPerTick = 10_000_000;
    
    public Engine()
    {
    }    
    
    public final void run()
    {
        initGLFW();
        loop();

        glfwFreeCallbacks(window);
        glfwDestroyWindow(window);

        glfwTerminate();
        GLFWErrorCallback error = glfwSetErrorCallback(null);
        if(error != null)
        {
            error.free();
        }
    }

    private void initGLFW()
    {
        GLFWErrorCallback.createPrint(System.err).set();
        
        if(!glfwInit())
        {
            throw new IllegalStateException("Unable to initialize GLFW");
        }

        glfwDefaultWindowHints();
        glfwWindowHint(GLFW_VISIBLE, GLFW_FALSE);
        glfwWindowHint(GLFW_RESIZABLE, GLFW_TRUE);

        window = glfwCreateWindow(Shader.getViewWidth(), Shader.getViewHeight(), "SnuviEngine " + VERSION, NULL, NULL);
        if(window == NULL)
        {
            throw new RuntimeException("Failed to create the GLFW window");
        }

        glfwSetKeyCallback(window, (w, key, scancode, action, mods) -> 
        {
            if(action == GLFW_RELEASE)
            {
                KeyHandler.onKeyUpEvent(key);
                if(key == GLFW_KEY_ESCAPE)
                {
                    glfwSetWindowShouldClose(window, true);
                }
            }
            else if(action == GLFW_PRESS)
            {
                KeyHandler.onKeyDownEvent(key);
            }
        });
        
        glfwSetFramebufferSizeCallback(window, (w, fwidth, fheight) -> 
        {
            glViewport(0, 0, fwidth, fheight);
            Shader.setViewPort(fwidth, fheight);
        });
        
        //glfwSetWindowAspectRatio(window, 16, 9);
        
        glfwMakeContextCurrent(window);
        glfwSwapInterval(1);
       
        glfwShowWindow(window);
    }

    private void loop()
    {
        GL.createCapabilities();
        
        long lastFrame = System.nanoTime();
        long lastTick = System.nanoTime();
        long time;
        long lag = 0;
        
        Shader.init();
        init();
        
        while(!glfwWindowShouldClose(window))
        {
            glfwSwapBuffers(window);
            glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

            time = System.nanoTime();
            fpsSum -= fps[fpsIndex];
            fps[fpsIndex] = time - lastFrame;
            fpsSum += fps[fpsIndex];
            lag += fps[fpsIndex];
            fpsIndex = (fpsIndex + 1) % fps.length;
            lastFrame = time;
            currentFps = (1_000_000_000.0 * fps.length) / fpsSum;

            while(lag >= nanosPerTick)
            {
                lag -= nanosPerTick;
                
                time = System.nanoTime();
                tpsSum -= tps[tpsIndex];
                tps[tpsIndex] = time - lastTick;
                tpsSum += tps[tpsIndex];
                tpsIndex = (tpsIndex + 1) % tps.length;
                lastTick = time;
                currentTps = (1_000_000_000.0 * tps.length) / tpsSum;
                
                KeyHandler.tick();
                tick();
            }
            
            Shader.doTasks();
            renderTick();

            glfwPollEvents();
        }
    }
    
    public final void setNanosPerTick(long nanos)
    {
        nanosPerTick = nanos;
    }
    
    public final double getTps()
    {
        return currentTps;
    }
    
    public final double getFps()
    {
        return currentFps;
    }
    
    public abstract void init();
    public abstract void tick();
    public abstract void renderTick();
}