using System.Drawing;
using OpenTK.Graphics.OpenGL;

namespace Dashboard.Drawing.OpenGL
{
    public class ContextExecutor : IDisposable
    {
        public GLEngine Engine { get; }
        public IGLContext Context { get; }
        public ContextResourcePool ResourcePool { get; }
        protected bool IsDisposed { get; private set; } = false;

        public bool IsInitialized { get; private set; } = false;

        private int _program = 0;
        public ContextExecutor(GLEngine engine, IGLContext context)
        {
            Engine = engine;
            Context = context;

            ResourcePool = Engine.ResourcePoolManager.Get(context);
            ResourcePool.IncrementReference();
        }

        ~ContextExecutor()
        {
            DisposeInvoker(false);
        }

        public void Initialize()
        {
            if (IsInitialized)
                return;
            IsInitialized = true;

            LoadShaders();
        }

        private void LoadShaders()
        {
            using Stream vsource = FetchEmbeddedResource("Dashboard.Drawing.OpenGL.default.vert");
            using Stream fsource = FetchEmbeddedResource("Dashboard.Drawing.OpenGL.default.frag");
            int vs = CompileShader(ShaderType.VertexShader, vsource);
            int fs = CompileShader(ShaderType.FragmentShader, fsource);
            _program = LinkProgram(vs, fs);
            GL.DeleteShader(vs);
            GL.DeleteShader(fs);
        }

        public void Draw(DrawQueue drawqueue) => Draw(drawqueue, new RectangleF(new PointF(0f,0f), Context.FramebufferSize));
        public virtual void Draw(DrawQueue drawQueue, RectangleF bounds)
        {

        }

        public virtual void EndFrame()
        {

        }

        private void DisposeInvoker(bool disposing)
        {
            if (!IsDisposed)
                return;

            IsDisposed = true;

            if (disposing)
                GC.SuppressFinalize(this);

            Dispose(disposing);
        }

        protected virtual void Dispose(bool disposing)
        {
            ContextCollector.Global.DeleteProgram(_program);
        }

        public void Dispose() => DisposeInvoker(true);

        private static int CompileShader(ShaderType type, string source)
        {
            int shader = GL.CreateShader(type);

            GL.ShaderSource(shader, source);
            GL.CompileShader(shader);

            int compileStatus = 0;
            GL.GetShaderi(shader, ShaderParameterName.CompileStatus, out compileStatus);

            if (compileStatus == 0)
            {
                GL.GetShaderInfoLog(shader, out string log);
                GL.DeleteShader(shader);
                throw new Exception($"{type} Shader compilation failed: " + log);
            }

            return shader;
        }

        private static int CompileShader(ShaderType type, Stream stream)
        {
            using StreamReader reader = new StreamReader(stream, leaveOpen: true);

            return CompileShader(type, reader.ReadToEnd());
        }

        private static int LinkProgram(int s1, int s2)
        {
            int program = GL.CreateProgram();

            GL.AttachShader(program, s1);
            GL.AttachShader(program, s2);

            GL.LinkProgram(program);

            int linkStatus = 0;
            GL.GetProgrami(program, ProgramProperty.LinkStatus, out linkStatus);
            if (linkStatus == 0)
            {
                GL.GetProgramInfoLog(program, out string log);
                GL.DeleteProgram(program);
                throw new Exception("Shader program linking failed: " + log);
            }

            return program;
        }

        private static Stream FetchEmbeddedResource(string name)
        {
            return typeof(ContextExecutor).Assembly.GetManifestResourceStream(name)!;
        }
    }
}