#include <GL/glx.h>
#include <GL/gl.h>
#include <unistd.h>
#include <iostream>

#include <stdlib.h>
#include <string.h>
#include <stdio.h>

#define GLX_CONTEXT_MAJOR_VERSION_ARB		0x2091
#define GLX_CONTEXT_MINOR_VERSION_ARB		0x2092
typedef GLXContext (*GLXCREATECONTEXTATTRIBSARBPROC)(Display*, GLXFBConfig, GLXContext, Bool, const int*);

bool CheckExtension(const char *string, const char *extensions)
{
/*
    const char *start;
    char *where, *terminator;

    // It takes a bit of care to be fool-proof about parsing the OpenGL extensions string. Don't be fooled by sub-strings, etc.
    start = extensions;
    while (true)
    {
        where = strstr(start, string);
        if (!where)
        {
            return false;
        }
        terminator = where + strlen(string);
        if (where == start || *(where - 1) == ' ')
        {
            if (*terminator == ' ' || *terminator == '\0')
            {
                break;
            }
        }
        start = terminator;
    }
*/
    return true;
}

int main (int argc, char ** argv)
{
	Display *display = XOpenDisplay(0);
	
	GLXCREATECONTEXTATTRIBSARBPROC glXCreateContextAttribsARB = NULL;
	
	const char *extensions = glXQueryExtensionsString(display, DefaultScreen(display));
	std::cout << extensions << std::endl;
	if (CheckExtension(extensions, "GLX_ARB_create_context"))
	{
	    glXCreateContextAttribsARB = (GLXCREATECONTEXTATTRIBSARBPROC)glXGetProcAddress((const GLubyte*)"glXCreateContextAttribsARB");
        if (glXCreateContextAttribsARB == NULL)
        {
            std::cout << "glXCreateContextAttribsARB entry point not found" << std::endl;
            return false;
    	}
	}
	else
	{
	    std::cout << "GL3 not supported." << std::endl;
        return 1;
	}

	static int visual_attribs[] =
	{
	    GLX_RENDER_TYPE, GLX_RGBA_BIT,
	    GLX_DRAWABLE_TYPE, GLX_WINDOW_BIT,
	    GLX_DOUBLEBUFFER, true,
	    GLX_RED_SIZE, 1,
	    GLX_GREEN_SIZE, 1,
	    GLX_BLUE_SIZE, 1,
	    None };

	std::cout << "Getting framebuffer config" << std::endl;
	int fbcount;
	GLXFBConfig *fbc = glXChooseFBConfig(display, DefaultScreen(display), visual_attribs, &fbcount);
	if (!fbc)
	{
		std::cout << "Failed to retrieve a framebuffer config" << std::endl;
		return 1;
	}

	std::cout << "Getting XVisualInfo" << std::endl;
	XVisualInfo *vi = glXGetVisualFromFBConfig(display, fbc[0]);

	XSetWindowAttributes swa;
    std::cout << "Creating colormap" << std::endl;
	swa.colormap = XCreateColormap(display, RootWindow(display, vi->screen), vi->visual, AllocNone);
	swa.border_pixel = 0;
	swa.event_mask = StructureNotifyMask;

	std::cout << "Creating window" << std::endl;
	Window win = XCreateWindow(display, RootWindow(display, vi->screen), 0, 0, 100, 100, 0, vi->depth, InputOutput, vi->visual, CWBorderPixel|CWColormap|CWEventMask, &swa);
    if (!win)
    {
        std::cout << "Failed to create window." << std::endl;
        return 1;
    }

	std::cout << "Mapping window" << std::endl;
	XMapWindow(display, win);

	//oldstyle context:
	//	GLXContext ctx = glXCreateContext(display, vi, 0, GL_TRUE);

    static int context_attribs[] = {
		GLX_CONTEXT_MAJOR_VERSION_ARB, 3,
		GLX_CONTEXT_MINOR_VERSION_ARB, 0,
		None};

    std::cout << "Creating context" << std::endl;
	GLXContext ctx = glXCreateContextAttribsARB(display, fbc[0], NULL, true, context_attribs);
	if (!ctx)
	{
	    std::cout << "Failed to create GL3 context." << std::endl;
	    return 1;
    }

    std::cout << "Making context current" << std::endl;
	glXMakeCurrent(display, win, ctx);

		glClearColor (0, 0.5, 1, 1);
		glClear (GL_COLOR_BUFFER_BIT);
		glXSwapBuffers (display, win);

		sleep(1);

		glClearColor (1, 0.5, 0, 1);
		glClear (GL_COLOR_BUFFER_BIT);
		glXSwapBuffers (display, win);

		sleep(1);

	ctx = glXGetCurrentContext(); 
	glXMakeCurrent(display, 0, 0);
	glXDestroyContext(display, ctx); 
}