use std::mem::MaybeUninit;

/// Safe wrapper for ucontext_t struct of linux-gnu libc
/// 
/// setcontext and getcontext are unsafe function, this wrap unsafe libc functions 
/// 
/// This struct doesn't work on windows, because this struct is unavailable
/// 
/// todo ucontext_t is not thread-safe (doesn't implements Send and Sync trait), and cannot be use in Threads as rust require var in Mutex (see system.rs) to have everything inside to implements thread-safe traits
#[derive(PartialEq)]
pub struct UContextT {
    #[cfg(not(target_os = "windows"))] // struct non disponible sur la libc sur windows
    pub buf: libc::ucontext_t,
    pub stack_bottom: Vec<i8>
}

#[cfg(not(target_os = "windows"))]
#[allow(unused)] // Temporary as we currently doesn't use this structure (this structure may disapear in a near future)
impl UContextT {

    pub fn new() -> Self {
        let mut context = MaybeUninit::<libc::ucontext_t>::uninit();
        unsafe { libc::getcontext(context.as_mut_ptr()) };
        Self {
            buf: unsafe  { context.assume_init() },
            stack_bottom: Vec::default(),
        }
    }

    /// Get user context and store it in variable pointed to by UCP.
    /// 
    /// Use `man getcontext` for more informations
    pub fn get_context(&mut self) -> i32 {
        unsafe {
            libc::getcontext(&mut self.buf)
        }
    }

    /// Set user context from information of variable pointed to by UCP.
    /// 
    /// Use `man setcontext` for more informations
    pub fn set_context(&mut self) -> i32 {
        unsafe {
            libc::setcontext(&self.buf)
        }
    }

    pub fn make_context(&mut self, func: extern "C" fn(), args: i32) {
        unsafe {
            libc::makecontext(&mut self.buf, func, args)
        }
    }
    
}

#[cfg(target_os = "windows")] 
impl UContextT {

    pub fn new() -> Self {
        Self {
            stack_bottom: Vec::default()
        }
    }

    pub fn get_context(&mut self) {
        // no op
    }

    pub fn set_context(&mut self) {
        // no op
    }
}