using OpenTK.Graphics.OpenGL4;
using OpenTK.Mathematics;
using OpenTK.Windowing.Common;
using OpenTK.Windowing.Desktop;
using OpenTK.Windowing.GraphicsLibraryFramework;
using VoxelEngine.Rendering;
using VoxelEngine.World;

namespace VoxelEngine.Core;

public sealed class Game : GameWindow
{
    private const float MoveSpeed = 8f;     // units per second
    private const float Sensitivity = 0.15f; // degrees per pixel

    private readonly BlockRegistry _registry = new();
    private Shader _shader = null!;
    private Texture _texture = null!;
    private ChunkRenderer _renderer = null!;
    private Camera _camera = null!;

    public Game(GameWindowSettings gameSettings, NativeWindowSettings nativeSettings)
        : base(gameSettings, nativeSettings) { }

    protected override void OnLoad()
    {
        base.OnLoad();

        GL.ClearColor(0.45f, 0.65f, 0.95f, 1.0f);
        GL.Enable(EnableCap.DepthTest);
        GL.Enable(EnableCap.CullFace);

        this._shader = new Shader("Assets/shaders/chunk.vert", "Assets/shaders/chunk.frag");
        this._texture = new Texture("Assets/textures/atlas.png");

        Chunk chunk = this.BuildChunk();
        float[] mesh = new ChunkMesher().Build(chunk, this._registry);
        this._renderer = new ChunkRenderer(mesh);

        this._camera = new Camera(new Vector3(8f, 20f, 40f), this.ClientSize.X / (float)this.ClientSize.Y);

        this.CursorState = CursorState.Grabbed;
    }

    private Chunk BuildChunk()
    {
        Chunk chunk = new();
        for (int x = 0; x < Chunk.Size; x++)
        for (int z = 0; z < Chunk.Size; z++)
        for (int y = 0; y < Chunk.Size; y++)
        {
            chunk[x, y, z] = y switch
            {
                Chunk.Size - 1 => this._registry.Grass.Id,
                >= Chunk.Size - 4 => this._registry.Dirt.Id,
                _ => this._registry.Stone.Id
            };
        }
        return chunk;
    }

    protected override void OnUpdateFrame(FrameEventArgs args)
    {
        base.OnUpdateFrame(args);
        if (!this.IsFocused) return;

        if (this.KeyboardState.IsKeyDown(Keys.Escape)) {
            this.Close(); return; }

        float distance = Game.MoveSpeed * (float)args.Time;
        if (this.KeyboardState.IsKeyDown(Keys.W)) this._camera.Move(this._camera.Front * distance);
        if (this.KeyboardState.IsKeyDown(Keys.S)) this._camera.Move(-this._camera.Front * distance);
        if (this.KeyboardState.IsKeyDown(Keys.A)) this._camera.Move(-this._camera.Right * distance);
        if (this.KeyboardState.IsKeyDown(Keys.D)) this._camera.Move(this._camera.Right * distance);
        if (this.KeyboardState.IsKeyDown(Keys.Space)) this._camera.Move(Vector3.UnitY * distance);
        if (this.KeyboardState.IsKeyDown(Keys.LeftShift)) this._camera.Move(-Vector3.UnitY * distance);

        Vector2 delta = this.MouseState.Delta;
        this._camera.AddRotation(delta.X * Game.Sensitivity, -delta.Y * Game.Sensitivity);
    }

    protected override void OnRenderFrame(FrameEventArgs args)
    {
        base.OnRenderFrame(args);

        GL.Clear(ClearBufferMask.ColorBufferBit | ClearBufferMask.DepthBufferBit);

        this._shader.Use();
        this._shader.SetMatrix4("model", Matrix4.Identity);
        this._shader.SetMatrix4("view", this._camera.GetViewMatrix());
        this._shader.SetMatrix4("projection", this._camera.GetProjectionMatrix());
        this._shader.SetInt("atlas", 0);
        this._texture.Use(TextureUnit.Texture0);
        this._renderer.Draw();

        this.SwapBuffers();
    }

    protected override void OnResize(ResizeEventArgs e)
    {
        base.OnResize(e);
        GL.Viewport(0, 0, e.Width, e.Height);
        // OnResize can fire before OnLoad (where _camera is created), so guard against it.
        if (this._camera is not null) this._camera.AspectRatio = e.Width / (float)e.Height;
    }

    protected override void OnUnload()
    {
        this._renderer.Dispose();
        this._texture.Dispose();
        this._shader.Dispose();
        base.OnUnload();
    }
}