#define GLEW_STATIC
// GLEW
#include <GL/glew.h>
#include <cstdlib>
#undef GLFW_DLL
// GLFW
#include <GLFW/glfw3.h>
#include <iostream>
#include <sstream>
#include <fstream>
#include <string>
using namespace std;


string readFile(const char *path){
    ifstream stream;
    stringstream ss;
    stream.exceptions(ifstream::badbit);
    try
    {
        stream.open(path);    // open file
        ss << stream.rdbuf(); // get strings from file
    } catch (ifstream::failure e)
    {
        cout << "ERROR::OPEN FILE:" << path << endl;
    }
    // close file handle
    stream.close();

    // get str() from stringstream
    string shaderCode = ss.str();
    return shaderCode;
}



void init(){


    string code =  readFile("shaders/feedback/CP_01.vert");
    const char * vertexShaderSrc = code.c_str();

    // Create shader and compile
    GLuint shader = glCreateShader(GL_VERTEX_SHADER);
    glShaderSource(shader, 1, &vertexShaderSrc, nullptr);
    glCompileShader(shader);

    // Create program and specify transform feedback variables
    GLuint program = glCreateProgram();
    glAttachShader(program, shader);

    // binding the out value
    const GLchar* feedbackVaryings[] = { "outValue" };
    glTransformFeedbackVaryings(program, 1, feedbackVaryings, GL_INTERLEAVED_ATTRIBS);

    // finally link program and use
    glLinkProgram(program);
    glUseProgram(program);

    // Create VAO
    GLuint vao;
    glGenVertexArrays(1, &vao);
    glBindVertexArray(vao);

    // Create input VBO and vertex format
    GLfloat data[] = { 1.0f, 2.0f, 3.0f, 4.0f, 5.0f };

    GLuint vbo;
    glGenBuffers(1, &vbo);
    glBindBuffer(GL_ARRAY_BUFFER, vbo);
    glBufferData(GL_ARRAY_BUFFER, sizeof(data), data, GL_STATIC_DRAW);

    GLint inputAttrib = glGetAttribLocation(program, "inValue");
    glEnableVertexAttribArray(inputAttrib);
    glVertexAttribPointer(inputAttrib, 1, GL_FLOAT, GL_FALSE, 0, 0);





    // Create transform feedback buffer
    GLuint tbo;
    glCreateBuffers(1, &tbo);
    glBindBuffer(GL_ARRAY_BUFFER, tbo);
    glBufferData(GL_ARRAY_BUFFER, sizeof(data), nullptr, GL_STATIC_READ);

    // Perform feedback transform
    glEnable(GL_RASTERIZER_DISCARD);

    glBindBufferBase(GL_TRANSFORM_FEEDBACK_BUFFER, 0, tbo);  // deafault


    glBeginTransformFeedback(GL_POINTS);
    glDrawArrays(GL_POINTS, 0, 5);
    glEndTransformFeedback();

    glDisable(GL_RASTERIZER_DISCARD);

    glFlush();

    // Fetch and print results
    GLfloat feedback[5];
    // parm1: target
    // parm2: offset
    // parm3: size
    // parm4: void *data
    // glGetBufferSubData(GL_TRANSFORM_FEEDBACK_BUFFER, 0, sizeof(feedback), feedback);


    //OGL 4.5 use-> glGetNamedBufferSubData()
    glGetNamedBufferSubData(tbo,0,sizeof(feedback), feedback);


    printf("%f %f %f %f %f\n", feedback[0], feedback[1], feedback[2], feedback[3], feedback[4]);

    glDeleteProgram(program);
    glDeleteShader(shader);

    glDeleteBuffers(1, &tbo);
    glDeleteBuffers(1, &vbo);

    glDeleteVertexArrays(1, &vao);


}





int main(){



    glfwInit();


    glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, 4);
    glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR, 5);
    glfwWindowHint(GLFW_OPENGL_PROFILE, GLFW_OPENGL_CORE_PROFILE);
    glfwWindowHint(GLFW_VISIBLE,GL_FALSE);
    GLFWwindow * window = glfwCreateWindow(800,600,"Hello",NULL,NULL);
    glfwMakeContextCurrent(window);


    // glew init
    glewInit();



/*
    while( !glfwWindowShouldClose( window ) ) {

        glfwPollEvents();
        glfwSwapBuffers(window);
    }
*/




    init();











    glfwTerminate();
    glfwDestroyWindow(window);

    return 0;
}