using System;
using System.Collections.Generic;
using System.Text;

using OpenGL;

namespace pEngine.Core.Graphics.Renderer
{
    public class Renderer
    {
        /// <summary>
        /// Creates a new instance of <see cref="Renderer"/>.
        /// </summary>
        public Renderer()
        {

        }

        /// <summary>
        /// Initialize all OpenGL related resources.
        /// </summary>
        public void Initialize()
        {
            InizializzaLaMerda();
        }

        #region Modules

        #endregion

        #region Ti prego cancellami

        string vs = @"
                            #version 330 core

                            layout(location = 0) in vec3 vertexPosition_modelspace;

                            void main()
                            {

                                gl_Position.xyz = vertexPosition_modelspace;
                                gl_Position.w = 1.0;
                            }
        ";

        string fs = @"
                            #version 330 core

                            out vec3 color;

                            void main()
                            {
                                color = vec3(1,0,0);
                            }
        ";

        uint vao;
        uint vertexbuffer;
        uint programID;

        float[] g_vertex_buffer_data = new float[9]
            {
                -1.0f, -1.0f, 0.0f,
                1.0f, -1.0f, 0.0f,
                0.0f,  1.0f, 0.0f,
            };

        void InizializzaLaMerda()
        {

            vao = Gl.GenVertexArray();
            Gl.BindVertexArray(vao);

            programID = LoadShader(vs, fs);

            // Generate 1 buffer, put the resulting identifier in vertexbuffer
            vertexbuffer = Gl.GenBuffer();
            // The following commands will talk about our 'vertexbuffer' buffer
            Gl.BindBuffer(BufferTargetARB.ArrayBuffer, vertexbuffer);
            // Give our vertices to OpenGL.
            Gl.BufferData(BufferTargetARB.ArrayBuffer, sizeof(float) * 9, g_vertex_buffer_data, BufferUsageARB.StaticDraw);
        }

        uint LoadShader(string vertContent, string fragContent)
        {
            uint VertexShaderID = Gl.CreateShader(Gl.VERTEX_SHADER);
            uint FragmentShaderID = Gl.CreateShader(Gl.FRAGMENT_SHADER);

            Gl.ShaderSource(VertexShaderID, new string[] { vertContent });
            Gl.CompileShader(VertexShaderID);

            Gl.ShaderSource(FragmentShaderID, new string[] { fragContent });
            Gl.CompileShader(FragmentShaderID);

            uint programId = Gl.CreateProgram();

            Gl.AttachShader(programId, VertexShaderID);
            Gl.AttachShader(programId, FragmentShaderID);
            Gl.LinkProgram(programId);

            Gl.DetachShader(programId, VertexShaderID);
            Gl.DetachShader(programId, FragmentShaderID);

            Gl.DeleteShader(VertexShaderID);
            Gl.DeleteShader(FragmentShaderID);

            return programId;
        }

        #endregion

        #region Rendering

        /// <summary>
        /// Takes all frame assets and draw it
        /// on the backbuffer.
        /// </summary>
        /// <param name="assets">Assets to draw.</param>
        public void DrawFrame(List<Asset> assets)
        {
            Gl.UseProgram(programID);

            // 1rst attribute buffer : vertices
            Gl.EnableVertexAttribArray(0);
            Gl.BindBuffer(BufferTargetARB.ArrayBuffer, vertexbuffer);
            Gl.VertexAttribPointer(
               0,                  // attribute 0. No particular reason for 0, but must match the layout in the shader.
               3,                  // size
               Gl.FLOAT,           // type
               false,           // normalized?
               0,                  // stride
               IntPtr.Zero            // array buffer offset
            );
            // Draw the triangle !
            Gl.DrawArrays(PrimitiveType.Triangles, 0, 3); // Starting from vertex 0; 3 vertices total -> 1 triangle
            Gl.DisableVertexAttribArray(0);
        }

        #endregion
    }
}