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 long fpsLimit = -1;
    private long sleep = 0;
    private long nanosPerTick = 10_000_000;
    private final int maxTicksPerFrame = 20;
    
    private final Timer fps = new Timer(60);
    private final Timer tps = new Timer(1_000_000_000l / nanosPerTick);
    
    public Engine()
    {
    }    
    
    public final void run()
    {
        initGLFW();
        loop();

        glfwFreeCallbacks(window);
        glfwDestroyWindow(window);

        glfwTerminate();
        GLFWErrorCallback error = glfwSetErrorCallback(null);
        if(error != null)
        {
            error.free();
        }
    }
    
    public final void stop()
    {
        glfwSetWindowShouldClose(window, true);
    }

    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);
            }
            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 sleep(long nanos)
    {
        if(nanos < 0)
        {
            sleep += nanos;
            return;
        }
        
        if(sleep < 0)
        {
            sleep += nanos / 4;
            nanos = (nanos * 3) / 4;
        }
        
        long end = System.nanoTime() + nanos - 10000;
        try
        {
            Thread.sleep(nanos / 1_000_000);
        }
        catch(InterruptedException ex)
        {
        }
        int i = 0;
        while(System.nanoTime() < end)
        {
            i++;
        }
    }

    private void loop()
    {
        GL.createCapabilities();
        
        Shader.init();
        init();
        
        fps.update();
        tps.update();
        long lag = 0;
        
        while(!glfwWindowShouldClose(window))
        {
            glfwSwapBuffers(window);
            
            glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

            if(fpsLimit > 0)
            {
                sleep(fpsLimit - fps.getCurrentTime());
            }
            fps.update();
            lag += fps.getTime();

            int ticksPerFrame = 0;
            while(lag >= nanosPerTick)
            {
                lag -= nanosPerTick;
                
                tps.update();
                
                KeyHandler.tick();
                tick();
                
                ticksPerFrame++;
                if(ticksPerFrame >= maxTicksPerFrame)
                {
                    long skip = lag / nanosPerTick;
                    lag -= skip * nanosPerTick;
                    if(skip > 0)
                    {
                        System.out.println("skipped " + skip + " game ticks " + lag);
                    }
                    break;
                }
            }
            
            Shader.doTasks();
            
            renderTick((float) lag / nanosPerTick);
            
            tps.draw();
            fps.draw();

            glfwPollEvents();
        }
    }
    
    public final void setNanosPerTick(long nanos)
    {
        nanosPerTick = nanos;
        tps.setExpectedValue(1_000_000_000l / nanos);
    }
    
    public final long getNanosPerTick()
    {
        return nanosPerTick;
    }
    
    public final double getTps()
    {
        return tps.getCallsPerSecond();
    }
    
    public final void setRenderTps(boolean active)
    {
        tps.setActive(active);
    }
    
    public final double getFps()
    {
        return fps.getCallsPerSecond();
    }
    
    public final void setMaxFps(int max)
    {
        fpsLimit = 1_000_000_000 / max;
    }
    
    public final void setRenderFps(boolean active)
    {
        fps.setActive(active);
    }
    
    public abstract void init();
    public abstract void tick();
    public abstract void renderTick(float lag);
}