import std.stdio;
import std.conv;

import derelict.glfw3.glfw3;
import derelict.opengl3.gl;

extern(C) void glfw_error_callback(int error, const(char) *description) nothrow {
    printf("%s\n", description);
}

void draw(GLFWwindow *window) {
    int width;
    int height;
    glfwGetFramebufferSize(window, &width, &height);
    glViewport(0, 0, width, height);

    glMatrixMode(GL_PROJECTION);
    glLoadIdentity();
    glOrtho(0, width, height, 0, -1, 1);
    glMatrixMode(GL_MODELVIEW);
    glLoadIdentity();

    glClearColor(0, 0, 0, 1);
    glClear(GL_DEPTH_BUFFER_BIT | GL_COLOR_BUFFER_BIT);

    glBegin(GL_QUADS);
    glColor4f(1, 0, 0, 1); glVertex2f(0, 0);
    glColor4f(0, 1, 0, 1); glVertex2f(0, 1);
    glColor4f(0, 0, 1, 1); glVertex2f(1, 1);
    glColor4f(1, 0, 1, 1); glVertex2f(1, 0);
    glEnd();

    glFlush();
}

void main() {
    DerelictGLFW3.load();
    DerelictGL.load();

    if(glfwInit() != GLFW_TRUE) {
        glfwTerminate();
        writeln("Failed to initialize GLFW3");
        return;
    }

    printf("GLFW Version: %s\n", glfwGetVersionString());

    glfwWindowHint(GLFW_DOUBLEBUFFER, GLFW_TRUE);
    glfwSetErrorCallback(&glfw_error_callback);

    GLFWwindow *window = glfwCreateWindow(800, 600, "The Source", null, null);
    if(!window) {
        glfwTerminate();
        writeln("Failed to initialize window");
        return;
    }

    glfwMakeContextCurrent(window);

    printf("OpenGL Version: %s\n", glGetString(GL_VERSION));

    glfwSwapInterval(1);

    writeln("Welcome to the Source.");

    stdout.flush();

    while(!glfwWindowShouldClose(window)) {
        draw(window);

        glfwSwapBuffers(window);
        glfwPollEvents();
    }

    glfwTerminate();
}