fn main() {
    unsafe {
        let mut ctx1 = Context::new();
        println!("&ctx1 = {:p}", &ctx1);
        println!("&CURRENT_CONTEXT = {:p}", &CURRENT_CONTEXT);
        set_current_context(&mut ctx1);

        let current_context = current_context();
        println!("current_context = {:p}", current_context);
    }
    unsafe {
        let mut ctx2 = Context::new();
        println!("&ctx2 = {:p}", &ctx2);
        println!("&CURRENT_CONTEXT = {:p}", &CURRENT_CONTEXT);
        set_current_context(&mut ctx2);

        let current_context = current_context();
        println!("current_context = {:p}", current_context);
    }
    {
        let current_context = current_context();
        println!("block3--current_context = {:p}", current_context);
    }
    {
        let current_context = current_context_mut();
        println!("block4--current_context = {:p}", current_context);
        current_context.state_manager.frame_buffer_id = 30;
        println!("block4--current_context = {}", current_context.state_manager.frame_buffer_id);
    }
    {
        let current_context = current_context();
        println!("block5--current_context = {}", current_context.state_manager.frame_buffer_id);
    }
    {
        let current_context = current_context_mut();
        println!("block6--current_context = {:p}", current_context);
        current_context.state_manager.frame_buffer_id = 30;
        println!("block6--current_context = {}", current_context.state_manager.frame_buffer_id);
    }
}

static mut CURRENT_CONTEXT: *mut Context = std::ptr::null_mut();

fn set_current_context(context: *mut Context) {
    unsafe {
        CURRENT_CONTEXT = context;
    }
}

fn current_context<'a>() -> &'a Context {
    unsafe { &*CURRENT_CONTEXT }
}

fn current_context_mut<'a>() -> &'a mut Context {
    unsafe { &mut *CURRENT_CONTEXT }
}

pub struct Context {
    pub resource_manager: ResourceManager,
    pub state_manager: StateManager,
}

impl Context{
    pub fn new() -> Self {
        Self {
            resource_manager: ResourceManager::new(),
            state_manager: StateManager::new(),
        }
    }
}

pub struct ResourceManager {

}

impl ResourceManager {
    pub fn new() -> Self {
        Self {

        }
    }
}

pub struct StateManager {
    pub frame_buffer_id: i32,
}

impl StateManager {
    pub fn new() -> Self {
        Self {
            frame_buffer_id: 0,
        }
    }
}