use crate::utility::list::List;
use crate::kernel::thread::Thread;
use crate::simulator::interrupt::InterruptStatus::InterruptOff;
use crate::simulator::machine::Machine;
use std::cell::RefCell;
use std::rc::Rc;
use super::thread_manager::ThreadManager;

///     Structure of a Semaphore used for synchronisation
#[derive(PartialEq)]
pub struct Semaphore {

    /// Counter of simultanous Semaphore
    pub counter:i32,
    /// QUeue of Semaphore waiting to be exucated
    pub waiting_queue:List<Rc<RefCell<Thread>>>,

}

impl Semaphore {

    ///     Initializes a semaphore, so that it can be used for synchronization.
    ///
    ///  ### Parameters
    /// - *counter* initial value of counter
    /// - *thread_manager* Thread manager which managing threads
    pub fn new(counter: i32) -> Semaphore{
        Semaphore { counter, waiting_queue: List::default() }
    }
    
}

/// Lock used for synchronisation, can be interpreted has a Semaphore with a
/// counter of 1
/// It's used for critical parts
#[derive(PartialEq)]
pub struct Lock {

    /// Thread owning the lock
    owner: Option<Rc<RefCell<Thread>>>,
    /// The queue of threads waiting for execution
    waiting_queue:List<Rc<RefCell<Thread>>>,
    /// A boolean definig if the lock is free or not
    free: bool

}

impl Lock {

    ///    Initialize a Lock, so that it can be used for synchronization.
    /// The lock is initialy free
    ///
    /// ### Parameters
    /// - **thread_manager** Thread manager which managing threads
    pub fn new() -> Lock {
        Lock { owner: None, waiting_queue: List::default(), free: true }
    }

    ///    Wait until the lock become free.  Checking the
    ///	state of the lock (free or busy) and modify it must be done
    ///	atomically, so we need to disable interrupts before checking
    ///	the value of free.
    ///
    ///	Note that thread_manager::thread_seep assumes that interrupts are disabled
    ///	when it is called.
    ///
    /// ### Parameters
    /// - **current_thread** the current thread
    /// - **machine** the machine where the threads are executed
    pub fn acquire(&mut self, machine: &mut Machine, thread_manager: &mut ThreadManager) {
        let old_status = machine.interrupt.set_status(InterruptOff);
        if self.free {
            self.free = false;
            self.owner = Option::Some(match thread_manager.get_g_current_thread() {
                Some(th) => {
                    Rc::clone(&th)
                },
                None => unreachable!()
            });
        } else {
            match thread_manager.get_g_current_thread() {
                Some(x) => {
                    let x = Rc::clone(&x);
                    self.waiting_queue.push(Rc::clone(&x));
                    thread_manager.thread_sleep(machine, Rc::clone(&x));
                },
                None => unreachable!("Current thread should not be None")
            }
        }

        machine.interrupt.set_status(old_status);
    }

    ///     Wake up a waiter if necessary, or release it if no thread is waiting.
    /// We check that the lock is held by the g_current_thread.
    ///	As with Acquire, this operation must be atomic, so we need to disable
    ///	interrupts.  scheduler::ready_to_run() assumes that threads
    ///	are disabled when it is called.
    ///
    /// ### Parameters
    /// - **machine** the machine where the code is executed
    /// - **scheduler** the scheduler which determine which thread to execute
    pub fn release(&mut self, machine: &mut Machine, thread_manager: &mut ThreadManager) {
        let old_status = machine.interrupt.set_status(InterruptOff);
        
        match thread_manager.get_g_current_thread() {
            Some(_) => {
                if self.held_by_current_thread(thread_manager) {
                    match self.waiting_queue.pop() {
                        Some(thread) => {
                            self.owner = Some(thread);
                            match &self.owner {
                                Some(x) => thread_manager.ready_to_run(Rc::clone(&x)),
                                None => ()
                            }
                        },
                        None => {
                            self.free = true;
                            self.owner = None;
                        }
                    }
                }
            }
            None => ()
        }

        machine.interrupt.set_status(old_status);
    }

    ///    True if the current thread holds this lock.
    /// Useful for checking in Release, and in Condition operations below.
    pub fn held_by_current_thread(&mut self, thread_manager: &mut ThreadManager) -> bool {
        match &self.owner {
            Some(x) => 
                match thread_manager.get_g_current_thread() {
                    Some(thread) => Rc::ptr_eq(x, thread),
                    None => false
                }
            None => false
        }
    }
}

/// Structure of a condition used for synchronisation
#[allow(unused)] // -> No enough time to implement it
pub struct Condition{

    /// The queue of threads waiting for execution
    waiting_queue:List<Rc<RefCell<Thread>>>,
    
}

impl Condition {

    /// Initializes a Condition, so that it can be used for synchronization.
    ///
    /// ### Parameters
    /// - *thread_manager* Thread manager which managing threads
    #[allow(unused)]
    pub fn new() -> Condition {
        Condition{ waiting_queue: List::default()}
    }

    ///  Block the calling thread (put it in the wait queue).
    ///  This operation must be atomic, so we need to disable interrupts.
    ///
    /// ### Parameters
    /// - **current_thread** the current thread
    /// - **machine** the machine where threads are executed
    #[allow(unused)]
    pub fn wait(&mut self, machine: &mut Machine, thread_manager: &mut ThreadManager) {
        let old_status = machine.interrupt.set_status(InterruptOff);
        match thread_manager.get_g_current_thread() {
            Some(thread) => {
                let rc1 = Rc::clone(thread);
                let rc2 = Rc::clone(thread);
                self.waiting_queue.push(rc1);
                thread_manager.thread_sleep(machine, rc2);
            },
            None => unreachable!()
        }

        machine.interrupt.set_status(old_status);
    }

    /// Wake up the first thread of the wait queue (if any).
    /// This operation must be atomic, so we need to disable interrupts.
    ///
    /// ### Parameters
    /// - **machine** the machine where the code is executed
    /// - **scheduler** the scheduler which determine which thread to execute
    #[allow(unused)]
    pub fn signal(&mut self, machine: &mut Machine, thread_manager: &mut ThreadManager) {
        let old_status = machine.interrupt.set_status(InterruptOff);

        match self.waiting_queue.pop() {
            Some(thread) => thread_manager.ready_to_run(thread),
            None => ()
        }

        machine.interrupt.set_status(old_status);

    }

    /// Wake up all threads waiting in the waitqueue of the condition
    /// This operation must be atomic, so we need to disable interrupts.
    ///
    /// ### Parameters
    /// - **machine** the machine where the code is executed
    /// - **scheduler** the scheduler which determine which thread to execute
    #[allow(unused)]
    pub fn broadcast(&mut self, machine: &mut Machine, thread_manager: &mut ThreadManager) {
        let old_status = machine.interrupt.set_status(InterruptOff);

        match self.waiting_queue.pop() {
            Some(thread) => thread_manager.ready_to_run(thread),
            None => ()
        }
        machine.interrupt.set_status(old_status);

    }

}

#[cfg(test)]
mod test {
    use std::{rc::Rc, cell::RefCell};

    use crate::{kernel::{thread::Thread, synch::Lock, thread_manager::ThreadManager}, simulator::machine::Machine};



    #[test]
    fn test_lock_simple() {
        let mut machine = Machine::new(true);
        let mut tm = ThreadManager::new();
        let thread = Rc::new(RefCell::new(Thread::new("test_lock")));
        tm.ready_to_run(Rc::clone(&thread));
        tm.set_g_current_thread(Some(Rc::clone(&thread)));
        let mut lock = Lock::new();

        assert!(lock.free);
        lock.acquire(&mut machine, &mut tm);
        assert!(lock.held_by_current_thread(&mut tm));

        assert!(!lock.free);
        lock.release(&mut machine, &mut tm);
        assert!(!lock.held_by_current_thread(&mut tm));
        assert!(lock.free);
    }

    #[test]
    fn test_lock_multiple() {
        let thread1 = Rc::new(RefCell::new(Thread::new("test_lock1")));
        let thread2 = Rc::new(RefCell::new(Thread::new("test_lock2")));

        let mut machine = Machine::new(true);
        let mut tm = ThreadManager::new();
        
        tm.ready_to_run(Rc::clone(&thread1));
        tm.ready_to_run(Rc::clone(&thread2));

        tm.set_g_current_thread(Some(Rc::clone(&thread1)));
        let mut lock = Lock::new();

        assert!(lock.free);
        lock.acquire(&mut machine, &mut tm);
        assert!(lock.held_by_current_thread(&mut tm));
        assert!(!lock.free);

        tm.set_g_current_thread(Some(Rc::clone(&thread2)));
        lock.acquire(&mut machine, &mut tm);
        
        
        tm.set_g_current_thread(Some(Rc::clone(&thread1)));
        assert!(lock.held_by_current_thread(&mut tm));
        assert!(lock.waiting_queue.iter().count() == 1);
        assert!(!lock.free);

        lock.release(&mut machine, &mut tm);
        assert!(!lock.held_by_current_thread(&mut tm));
        
        tm.set_g_current_thread(Some(Rc::clone(&thread2)));
        assert!(lock.held_by_current_thread(&mut tm));
        assert!(!lock.free);

        lock.release(&mut machine, &mut tm);
        assert!(!lock.held_by_current_thread(&mut tm));
        assert!(lock.free);
    }
}