#include <windows.h>
#include <GL/gl.h>

// Global variables
HINSTANCE hInstance;
HWND hWnd;
HDC hDC;
HGLRC hRC;

// Forward declarations
LRESULT CALLBACK WndProc(HWND, UINT, WPARAM, LPARAM);
void EnableOpenGL(HWND, HDC*, HGLRC*);
void DisableOpenGL(HWND, HDC, HGLRC);

int WINAPI WinMain(HINSTANCE hInst, HINSTANCE hPrevInstance, LPSTR lpCmdLine, int nCmdShow)
{
    // Register the window class
    WNDCLASSEX wc = {
        sizeof(WNDCLASSEX),
        CS_CLASSDC,
        WndProc,
        0L,
        0L,
        hInst,
        NULL,
        NULL,
        NULL,
        NULL,
        "GLSample",
        NULL
    };
    RegisterClassEx(&wc);

    // Create the window
    hWnd = CreateWindowEx(
            0,
            "GLSample",
            "OpenGL Sample",
            WS_OVERLAPPEDWINDOW,
            CW_USEDEFAULT,
            CW_USEDEFAULT,
            256,
            256,
            NULL,
            NULL,
            hInst,
            NULL
    );

    // Enable OpenGL
    EnableOpenGL(hWnd, &hDC, &hRC);

    // Show the window
    ShowWindow(hWnd, nCmdShow);
    UpdateWindow(hWnd);

    // Main loop
    MSG msg;
    while (GetMessage(&msg, NULL, 0, 0))
    {
        TranslateMessage(&msg);
        DispatchMessage(&msg);
    }

    // Disable OpenGL
    DisableOpenGL(hWnd, hDC, hRC);

    // Clean up
    UnregisterClass("GLSample", hInstance);
    return msg.wParam;
}

LRESULT CALLBACK WndProc(HWND hWnd, UINT message, WPARAM wParam, LPARAM lParam)
{
    switch (message)
    {
    case WM_CLOSE:
        PostQuitMessage(0);
        break;
    case WM_SIZE:
        glViewport(0, 0, LOWORD(lParam), HIWORD(lParam));
        break;
    case WM_PAINT:
        {
            PAINTSTRUCT ps;
            BeginPaint(hWnd, &ps);

            // Clear the screen
            glClearColor(0.0f, 0.0f, 0.0f, 1.0f);
            glClear(GL_COLOR_BUFFER_BIT);

            // Draw a triangle
            glBegin(GL_TRIANGLES);
            glColor3f(1.0f, 0.0f, 0.0f);
            glVertex2f(-0.5f, -0.5f);
            glColor3f(0.0f, 1.0f, 0.0f);
            glVertex2f(0.5f, -0.5f);
            glColor3f(0.0f, 0.0f, 1.0f);
            glVertex2f(0.0f, 0.5f);
            glEnd();

            // Swap buffers
            SwapBuffers(hDC);

            EndPaint(hWnd, &ps);
        }
        break;
    default:
        return DefWindowProc(hWnd, message, wParam, lParam);
    }
    return 0;
}

void EnableOpenGL(HWND hWnd, HDC* hDC, HGLRC* hRC)
{
    *hDC = GetDC(hWnd);

    // Set the pixel format
    PIXELFORMATDESCRIPTOR pfd = {
        sizeof(PIXELFORMATDESCRIPTOR),
        1,
        PFD_DRAW_TO_WINDOW | PFD_SUPPORT_OPENGL | PFD_DOUBLEBUFFER,
        PFD_TYPE_RGBA,
        32,
        0, 0, 0, 0, 0, 0,
        0,
        0,
        0,
        0, 0, 0, 0,
        16,
        0,
        0,
        PFD_MAIN_PLANE,
        0,
        0, 0, 0
    };

    int iFormat = ChoosePixelFormat(*hDC, &pfd);
    SetPixelFormat(*hDC, iFormat, &pfd);

    // Create the OpenGL context
    *hRC = wglCreateContext(*hDC);
    wglMakeCurrent(*hDC, *hRC);
}

void DisableOpenGL(HWND hWnd, HDC hDC, HGLRC hRC)
{
    wglMakeCurrent(NULL, NULL);
    wglDeleteContext(hRC);
    ReleaseDC(hWnd, hDC);
}